Subject: [PATCH 1/2] [RFC PATCH v6] dmabuf-sync: Add a buffer synchronization framework

From: [email-masked] (Konrad Rzeszutek Wilk)
Date: Tue, 20 Aug 2013 15:22:28 -0400

On Tue, Aug 13, 2013 at 06:19:35PM +0900, Inki Dae wrote:
> This patch adds a buffer synchronization framework based on DMA BUF[1]
> and and based on ww-mutexes[2] for lock mechanism.
> 
> The purpose of this framework is to provide not only buffer access control
> to CPU and DMA but also easy-to-use interfaces for device drivers and
> user application. This framework can be used for all dma devices using
> system memory as dma buffer, especially for most ARM based SoCs.
> 
> Changelog v6:
> - Fix sync lock to multiple reads.
> - Add select system call support.
>   . Wake up poll_wait when a dmabuf is unlocked.
> - Remove unnecessary the use of mutex lock.
> - Add private backend ops callbacks.
>   . This ops has one callback for device drivers to clean up their
>     sync object resource when the sync object is freed. For this,
>     device drivers should implement the free callback properly.
> - Update document file.
> 
> Changelog v5:
> - Rmove a dependence on reservation_object: the reservation_object is used
>   to hook up to ttm and dma-buf for easy sharing of reservations across
>   devices. However, the dmabuf sync can be used for all dma devices; v4l2
>   and drm based drivers, so doesn't need the reservation_object anymore.
>   With regared to this, it adds 'void *sync' to dma_buf structure.
> - All patches are rebased on mainline, Linux v3.10.
> 
> Changelog v4:
> - Add user side interface for buffer synchronization mechanism and update
>   descriptions related to the user side interface.
> 
> Changelog v3:
> - remove cache operation relevant codes and update document file.
> 
> Changelog v2:
> - use atomic_add_unless to avoid potential bug.
> - add a macro for checking valid access type.
> - code clean.
> 
> The mechanism of this framework has the following steps,
>     1. Register dmabufs to a sync object - A task gets a new sync object and
>     can add one or more dmabufs that the task wants to access.
>     This registering should be performed when a device context or an event
>     context such as a page flip event is created or before CPU accesses a shared
>     buffer.
> 
> 	dma_buf_sync_get(a sync object, a dmabuf);
> 
>     2. Lock a sync object - A task tries to lock all dmabufs added in its own
>     sync object. Basically, the lock mechanism uses ww-mutex[1] to avoid dead
>     lock issue and for race condition between CPU and CPU, CPU and DMA, and DMA
>     and DMA. Taking a lock means that others cannot access all locked dmabufs
>     until the task that locked the corresponding dmabufs, unlocks all the locked
>     dmabufs.
>     This locking should be performed before DMA or CPU accesses these dmabufs.
> 
> 	dma_buf_sync_lock(a sync object);
> 
>     3. Unlock a sync object - The task unlocks all dmabufs added in its own sync
>     object. The unlock means that the DMA or CPU accesses to the dmabufs have
>     been completed so that others may access them.
>     This unlocking should be performed after DMA or CPU has completed accesses
>     to the dmabufs.
> 
> 	dma_buf_sync_unlock(a sync object);
> 
>     4. Unregister one or all dmabufs from a sync object - A task unregisters
>     the given dmabufs from the sync object. This means that the task dosen't
>     want to lock the dmabufs.
>     The unregistering should be performed after DMA or CPU has completed
>     accesses to the dmabufs or when dma_buf_sync_lock() is failed.
> 
> 	dma_buf_sync_put(a sync object, a dmabuf);
> 	dma_buf_sync_put_all(a sync object);
> 
>     The described steps may be summarized as:
> 	get -> lock -> CPU or DMA access to a buffer/s -> unlock -> put
> 
> This framework includes the following two features.
>     1. read (shared) and write (exclusive) locks - A task is required to declare
>     the access type when the task tries to register a dmabuf;
>     READ, WRITE, READ DMA, or WRITE DMA.
> 
>     The below is example codes,
> 	struct dmabuf_sync *sync;
> 
> 	sync = dmabuf_sync_init(...);
> 	...
> 
> 	dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_R);
> 	...
> 
> 	And the below can be used as access types:
> 		DMA_BUF_ACCESS_R - CPU will access a buffer for read.
> 		DMA_BUF_ACCESS_W - CPU will access a buffer for read or write.
> 		DMA_BUF_ACCESS_DMA_R - DMA will access a buffer for read
> 		DMA_BUF_ACCESS_DMA_W - DMA will access a buffer for read or
> 					write.
> 
>     2. Mandatory resource releasing - a task cannot hold a lock indefinitely.
>     A task may never try to unlock a buffer after taking a lock to the buffer.
>     In this case, a timer handler to the corresponding sync object is called
>     in five (default) seconds and then the timed-out buffer is unlocked by work
>     queue handler to avoid lockups and to enforce resources of the buffer.
> 
> The below is how to use interfaces for device driver:
> 	1. Allocate and Initialize a sync object:
> 		static void xxx_dmabuf_sync_free(void *priv)
> 		{
> 			struct xxx_context *ctx = priv;
> 
> 			if (!ctx)
> 				return;
> 
> 			ctx->sync = NULL;
> 		}
> 		...
> 
> 		static struct dmabuf_sync_priv_ops driver_specific_ops = {
> 			.free = xxx_dmabuf_sync_free,
> 		};
> 		...
> 
> 		struct dmabuf_sync *sync;
> 
> 		sync = dmabuf_sync_init("test sync", &driver_specific_ops, ctx);
> 		...
> 
> 	2. Add a dmabuf to the sync object when setting up dma buffer relevant
> 	   registers:
> 		dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_READ);
> 		...
> 
> 	3. Lock all dmabufs of the sync object before DMA or CPU accesses
> 	   the dmabufs:
> 		dmabuf_sync_lock(sync);
> 		...
> 
> 	4. Now CPU or DMA can access all dmabufs locked in step 3.
> 
> 	5. Unlock all dmabufs added in a sync object after DMA or CPU access
> 	   to these dmabufs is completed:
> 		dmabuf_sync_unlock(sync);
> 
> 	   And call the following functions to release all resources,
> 		dmabuf_sync_put_all(sync);
> 		dmabuf_sync_fini(sync);
> 
> 	You can refer to actual example codes:
> 		"drm/exynos: add dmabuf sync support for g2d driver" and
> 		"drm/exynos: add dmabuf sync support for kms framework" from
> 		https://git.kernel.org/cgit/linux/kernel/git/daeinki/
> 		drm-exynos.git/log/?h=dmabuf-sync
> 
> And this framework includes fcntl system call[3] as interfaces exported
> to user. As you know, user sees a buffer object as a dma-buf file descriptor.
> So fcntl() call with the file descriptor means to lock some buffer region being
> managed by the dma-buf object.
> 
> The below is how to use interfaces for user application:
> 
> fcntl system call:
> 
> 	struct flock filelock;
> 
> 	1. Lock a dma buf:
> 		filelock.l_type = F_WRLCK or F_RDLCK;
> 
> 		/* lock entire region to the dma buf. */
> 		filelock.lwhence = SEEK_CUR;
> 		filelock.l_start = 0;
> 		filelock.l_len = 0;
> 
> 		fcntl(dmabuf fd, F_SETLKW or F_SETLK, &filelock);
> 		...
> 		CPU access to the dma buf
> 
> 	2. Unlock a dma buf:
> 		filelock.l_type = F_UNLCK;
> 
> 		fcntl(dmabuf fd, F_SETLKW or F_SETLK, &filelock);
> 
> 		close(dmabuf fd) call would also unlock the dma buf. And for more
> 		detail, please refer to [3]
> 
> select system call:
> 
> 	fd_set wdfs or rdfs;
> 
> 	FD_ZERO(&wdfs or &rdfs);
> 	FD_SET(fd, &wdfs or &rdfs);
> 
> 	select(fd + 1, &rdfs, NULL, NULL, NULL);
> 		or
> 	select(fd + 1, NULL, &wdfs, NULL, NULL);
> 
> 	Every time select system call is called, a caller will wait for
> 	the completion of DMA or CPU access to a shared buffer if there
> 	is someone accessing the shared buffer; locked the shared buffer.
> 	However, if no anyone then select system call will be returned
> 	at once.
> 
> References:
> [1] http://lwn.net/Articles/470339/
> [2] https://patchwork.kernel.org/patch/2625361/
> [3] http://linux.die.net/man/2/fcntl
> 
> Signed-off-by: Inki Dae <[email-masked]>
> Signed-off-by: Kyungmin Park <[email-masked]>
> ---
>  Documentation/dma-buf-sync.txt |  285 +++++++++++++++++
>  drivers/base/Kconfig           |    7 +
>  drivers/base/Makefile          |    1 +
>  drivers/base/dma-buf.c         |    4 +
>  drivers/base/dmabuf-sync.c     |  678 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-buf.h        |   16 +
>  include/linux/dmabuf-sync.h    |  190 +++++++++++
>  7 files changed, 1181 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/dma-buf-sync.txt
>  create mode 100644 drivers/base/dmabuf-sync.c
>  create mode 100644 include/linux/dmabuf-sync.h
> 
> diff --git a/Documentation/dma-buf-sync.txt b/Documentation/dma-buf-sync.txt
> new file mode 100644
> index 0000000..8023d06
> --- /dev/null
> +++ b/Documentation/dma-buf-sync.txt
> @@ -0,0 +1,285 @@
> +                    DMA Buffer Synchronization Framework
> +                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +                                  Inki Dae
> +                      <inki dot dae@samsung dot com>
> +                          <daeinki@gmail dot com>
> +
> +This document is a guide for device-driver writers describing the DMA buffer
> +synchronization API. This document also describes how to use the API to
> +use buffer synchronization mechanism between DMA and DMA, CPU and DMA, and
> +CPU and CPU.
> +
> +The DMA Buffer synchronization API provides buffer synchronization mechanism;
> +i.e., buffer access control to CPU and DMA, and easy-to-use interfaces for
> +device drivers and user application. And this API can be used for all dma
> +devices using system memory as dma buffer, especially for most ARM based SoCs.
> +
> +
> +Motivation
> +----------
> +
> +Buffer synchronization issue between DMA and DMA:
> +	Sharing a buffer, a device cannot be aware of when the other device
> +	will access the shared buffer: a device may access a buffer containing
> +	wrong data if the device accesses the shared buffer while another
> +	device is still accessing the shared buffer.
> +	Therefore, a user process should have waited for the completion of DMA
> +	access by another device before a device tries to access the shared
> +	buffer.
> +
> +Buffer synchronization issue between CPU and DMA:
> +	A user process should consider that when having to send a buffer, filled
> +	by CPU, to a device driver for the device driver to access the buffer as
> +	a input buffer while CPU and DMA are sharing the buffer.
> +	This means that the user process needs to understand how the device
> +	driver is worked. Hence, the conventional mechanism not only makes
> +	user application complicated but also incurs performance overhead.
> +
> +Buffer synchronization issue between CPU and CPU:
> +	In case that two processes share one buffer; shared with DMA also,
> +	they may need some mechanism to allow process B to access the shared
> +	buffer after the completion of CPU access by process A.
> +	Therefore, process B should have waited for the completion of CPU access
> +	by process A using the mechanism before trying to access the shared
> +	buffer.
> +
> +What is the best way to solve these buffer synchronization issues?
> +	We may need a common object that a device driver and a user process
> +	notify the common object of when they try to access a shared buffer.
> +	That way we could decide when we have to allow or not to allow for CPU
> +	or DMA to access the shared buffer through the common object.
> +	If so, what could become the common object? Right, that's a dma-buf[1].
> +	Now we have already been using the dma-buf to share one buffer with
> +	other drivers.
> +
> +
> +Basic concept
> +-------------
> +
> +The mechanism of this framework has the following steps,
> +    1. Register dmabufs to a sync object - A task gets a new sync object and
> +    can add one or more dmabufs that the task wants to access.
> +    This registering should be performed when a device context or an event
> +    context such as a page flip event is created or before CPU accesses a shared
> +    buffer.
> +
> +	dma_buf_sync_get(a sync object, a dmabuf);
> +
> +    2. Lock a sync object - A task tries to lock all dmabufs added in its own
> +    sync object. Basically, the lock mechanism uses ww-mutexes[2] to avoid dead
> +    lock issue and for race condition between CPU and CPU, CPU and DMA, and DMA
> +    and DMA. Taking a lock means that others cannot access all locked dmabufs
> +    until the task that locked the corresponding dmabufs, unlocks all the locked
> +    dmabufs.
> +    This locking should be performed before DMA or CPU accesses these dmabufs.
> +
> +	dma_buf_sync_lock(a sync object);
> +
> +    3. Unlock a sync object - The task unlocks all dmabufs added in its own sync
> +    object. The unlock means that the DMA or CPU accesses to the dmabufs have
> +    been completed so that others may access them.
> +    This unlocking should be performed after DMA or CPU has completed accesses
> +    to the dmabufs.
> +
> +	dma_buf_sync_unlock(a sync object);
> +
> +    4. Unregister one or all dmabufs from a sync object - A task unregisters
> +    the given dmabufs from the sync object. This means that the task dosen't
> +    want to lock the dmabufs.
> +    The unregistering should be performed after DMA or CPU has completed
> +    accesses to the dmabufs or when dma_buf_sync_lock() is failed.
> +
> +	dma_buf_sync_put(a sync object, a dmabuf);
> +	dma_buf_sync_put_all(a sync object);
> +
> +    The described steps may be summarized as:
> +	get -> lock -> CPU or DMA access to a buffer/s -> unlock -> put
> +
> +This framework includes the following two features.
> +    1. read (shared) and write (exclusive) locks - A task is required to declare
> +    the access type when the task tries to register a dmabuf;
> +    READ, WRITE, READ DMA, or WRITE DMA.
> +
> +    The below is example codes,
> +	struct dmabuf_sync *sync;
> +
> +	sync = dmabuf_sync_init(NULL, "test sync");
> +
> +	dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_R);
> +	...
> +
> +    2. Mandatory resource releasing - a task cannot hold a lock indefinitely.
> +    A task may never try to unlock a buffer after taking a lock to the buffer.
> +    In this case, a timer handler to the corresponding sync object is called
> +    in five (default) seconds and then the timed-out buffer is unlocked by work
> +    queue handler to avoid lockups and to enforce resources of the buffer.
> +
> +
> +Access types
> +------------
> +
> +DMA_BUF_ACCESS_R - CPU will access a buffer for read.
> +DMA_BUF_ACCESS_W - CPU will access a buffer for read or write.
> +DMA_BUF_ACCESS_DMA_R - DMA will access a buffer for read
> +DMA_BUF_ACCESS_DMA_W - DMA will access a buffer for read or write.
> +
> +
> +Generic user interfaces
> +-----------------------
> +
> +And this framework includes fcntl system call[3] as interfaces exported
> +to user. As you know, user sees a buffer object as a dma-buf file descriptor.
> +So fcntl() call with the file descriptor means to lock some buffer region being
> +managed by the dma-buf object.
> +
> +
> +API set
> +-------
> +
> +bool is_dmabuf_sync_supported(void)
> +	- Check if dmabuf sync is supported or not.
> +
> +struct dmabuf_sync *dmabuf_sync_init(const char *name,
> +					struct dmabuf_sync_priv_ops *ops,
> +					void priv*)
> +	- Allocate and initialize a new sync object. The caller can get a new
> +	sync object for buffer synchronization. ops is used for device driver
> +	to clean up its own sync object. For this, each device driver should
> +	implement a free callback. priv is used for device driver to get its
> +	device context when free callback is called.
> +
> +void dmabuf_sync_fini(struct dmabuf_sync *sync)
> +	- Release all resources to the sync object.
> +
> +int dmabuf_sync_get(struct dmabuf_sync *sync, void *sync_buf,
> +			unsigned int type)
> +	- Get dmabuf sync object. Internally, this function allocates
> +	a dmabuf_sync object and adds a given dmabuf to it, and also takes
> +	a reference to the dmabuf. The caller can tie up multiple dmabufs
> +	into one sync object by calling this function several times.
> +
> +void dmabuf_sync_put(struct dmabuf_sync *sync, struct dma_buf *dmabuf)
> +	- Put dmabuf sync object to a given dmabuf. Internally, this function
> +	removes a given dmabuf from a sync object and remove the sync object.
> +	At this time, the dmabuf is putted.
> +
> +void dmabuf_sync_put_all(struct dmabuf_sync *sync)
> +	- Put dmabuf sync object to dmabufs. Internally, this function removes
> +	all dmabufs from a sync object and remove the sync object.
> +	At this time, all dmabufs are putted.
> +
> +int dmabuf_sync_lock(struct dmabuf_sync *sync)
> +	- Lock all dmabufs added in a sync object. The caller should call this
> +	function prior to CPU or DMA access to the dmabufs so that others can
> +	not access the dmabufs. Internally, this function avoids dead lock
> +	issue with ww-mutexes.
> +
> +int dmabuf_sync_single_lock(struct dma_buf *dmabuf)
> +	- Lock a dmabuf. The caller should call this
> +	function prior to CPU or DMA access to the dmabuf so that others can
> +	not access the dmabuf.
> +
> +int dmabuf_sync_unlock(struct dmabuf_sync *sync)
> +	- Unlock all dmabufs added in a sync object. The caller should call
> +	this function after CPU or DMA access to the dmabufs is completed so
> +	that others can access the dmabufs.
> +
> +void dmabuf_sync_single_unlock(struct dma_buf *dmabuf)
> +	- Unlock a dmabuf. The caller should call this function after CPU or
> +	DMA access to the dmabuf is completed so that others can access
> +	the dmabuf.
> +
> +
> +Tutorial for device driver
> +--------------------------
> +
> +1. Allocate and Initialize a sync object:
> +	static void xxx_dmabuf_sync_free(void *priv)
> +	{
> +		struct xxx_context *ctx = priv;
> +
> +		if (!ctx)
> +			return;
> +
> +		ctx->sync = NULL;
> +	}
> +	...
> +
> +	static struct dmabuf_sync_priv_ops driver_specific_ops = {
> +		.free = xxx_dmabuf_sync_free,
> +	};
> +	...
> +
> +	struct dmabuf_sync *sync;
> +
> +	sync = dmabuf_sync_init("test sync", &driver_specific_ops, ctx);
> +	...
> +
> +2. Add a dmabuf to the sync object when setting up dma buffer relevant registers:
> +	dmabuf_sync_get(sync, dmabuf, DMA_BUF_ACCESS_READ);
> +	...
> +
> +3. Lock all dmabufs of the sync object before DMA or CPU accesses the dmabufs:
> +	dmabuf_sync_lock(sync);
> +	...
> +
> +4. Now CPU or DMA can access all dmabufs locked in step 3.
> +
> +5. Unlock all dmabufs added in a sync object after DMA or CPU access to these
> +   dmabufs is completed:
> +	dmabuf_sync_unlock(sync);
> +
> +   And call the following functions to release all resources,
> +	dmabuf_sync_put_all(sync);
> +	dmabuf_sync_fini(sync);
> +
> +
> +Tutorial for user application
> +-----------------------------
> +fcntl system call:
> +
> +	struct flock filelock;
> +
> +1. Lock a dma buf:
> +	filelock.l_type = F_WRLCK or F_RDLCK;
> +
> +	/* lock entire region to the dma buf. */
> +	filelock.lwhence = SEEK_CUR;
> +	filelock.l_start = 0;
> +	filelock.l_len = 0;
> +
> +	fcntl(dmabuf fd, F_SETLKW or F_SETLK, &filelock);
> +	...
> +	CPU access to the dma buf
> +
> +2. Unlock a dma buf:
> +	filelock.l_type = F_UNLCK;
> +
> +	fcntl(dmabuf fd, F_SETLKW or F_SETLK, &filelock);
> +
> +	close(dmabuf fd) call would also unlock the dma buf. And for more
> +	detail, please refer to [3]
> +
> +
> +select system call:
> +
> +	fd_set wdfs or rdfs;
> +
> +	FD_ZERO(&wdfs or &rdfs);
> +	FD_SET(fd, &wdfs or &rdfs);
> +
> +	select(fd + 1, &rdfs, NULL, NULL, NULL);
> +		or
> +	select(fd + 1, NULL, &wdfs, NULL, NULL);
> +
> +	Every time select system call is called, a caller will wait for
> +	the completion of DMA or CPU access to a shared buffer if there is
> +	someone accessing the shared buffer; locked the shared buffer.
> +	However, if no anyone then select system call will be returned
> +	at once.
> +
> +References:
> +[1] http://lwn.net/Articles/470339/
> +[2] https://patchwork.kernel.org/patch/2625361/
> +[3] http://linux.die.net/man/2/fcntl
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 5daa259..35e1518 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -200,6 +200,13 @@ config DMA_SHARED_BUFFER
>  	  APIs extension; the file's descriptor can then be passed on to other
>  	  driver.
>  
> +config DMABUF_SYNC
> +	bool "DMABUF Synchronization Framework"
> +	depends on DMA_SHARED_BUFFER
> +	help
> +	  This option enables dmabuf sync framework for buffer synchronization between
> +	  DMA and DMA, CPU and DMA, and CPU and CPU.
> +
>  config CMA
>  	bool "Contiguous Memory Allocator"
>  	depends on HAVE_DMA_CONTIGUOUS && HAVE_MEMBLOCK
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 48029aa..e06a5d7 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -11,6 +11,7 @@ obj-y			+= power/
>  obj-$(CONFIG_HAS_DMA)	+= dma-mapping.o
>  obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
>  obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o reservation.o
> +obj-$(CONFIG_DMABUF_SYNC) += dmabuf-sync.o
>  obj-$(CONFIG_ISA)	+= isa.o
>  obj-$(CONFIG_FW_LOADER)	+= firmware_class.o
>  obj-$(CONFIG_NUMA)	+= node.o
> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
> index 6687ba7..4aca57a 100644
> --- a/drivers/base/dma-buf.c
> +++ b/drivers/base/dma-buf.c
> @@ -29,6 +29,7 @@
>  #include <linux/export.h>
>  #include <linux/debugfs.h>
>  #include <linux/seq_file.h>
> +#include <linux/dmabuf-sync.h>
>  
>  static inline int is_dma_buf_file(struct file *);
>  
> @@ -56,6 +57,8 @@ static int dma_buf_release(struct inode *inode, struct file *file)
>  	list_del(&dmabuf->list_node);
>  	mutex_unlock(&db_list.lock);
>  
> +	dmabuf_sync_reservation_fini(dmabuf);
> +
>  	kfree(dmabuf);
>  	return 0;
>  }
> @@ -134,6 +137,7 @@ struct dma_buf *dma_buf_export_named(void *priv, const struct dma_buf_ops *ops,
>  
>  	file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf, flags);
>  
> +	dmabuf_sync_reservation_init(dmabuf);
>  	dmabuf->file = file;
>  
>  	mutex_init(&dmabuf->lock);
> diff --git a/drivers/base/dmabuf-sync.c b/drivers/base/dmabuf-sync.c
> new file mode 100644
> index 0000000..fbe711c
> --- /dev/null
> +++ b/drivers/base/dmabuf-sync.c
> @@ -0,0 +1,678 @@
> +/*
> + * Copyright (C) 2013 Samsung Electronics Co.Ltd
> + * Authors:
> + *	Inki Dae <[email-masked]>
> + *
> + * This program is free software; you can redistribute  it and/or modify it
> + * under  the terms of  the GNU General  Public License as published by the
> + * Free Software Foundation;  either version 2 of the  License, or (at your
> + * option) any later version.
> + *
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/debugfs.h>
> +#include <linux/uaccess.h>
> +
> +#include <linux/dmabuf-sync.h>
> +
> +#define MAX_SYNC_TIMEOUT	5 /* Second. */
> +
> +int dmabuf_sync_enabled = 1;
> +
> +MODULE_PARM_DESC(enabled, "Check if dmabuf sync is supported or not");
> +module_param_named(enabled, dmabuf_sync_enabled, int, 0444);
> +
> +DEFINE_WW_CLASS(dmabuf_sync_ww_class);
> +EXPORT_SYMBOL(dmabuf_sync_ww_class);
> +
> +static void dmabuf_sync_timeout_worker(struct work_struct *work)
> +{
> +	struct dmabuf_sync *sync = container_of(work, struct dmabuf_sync, work);
> +	struct dmabuf_sync_object *sobj;
> +
> +	mutex_lock(&sync->lock);
> +
> +	list_for_each_entry(sobj, &sync->syncs, head) {

You are using the 'sobj->robj' quite a lot. Why not just use a temp structure:

		struct dmabuf_sync_reservation *rsvp = sobj->robj;

and use that in this function. It would make it easier to read I think.

> +		BUG_ON(!sobj->robj);
> +
> +		mutex_lock(&sobj->robj->lock);
> +
> +		printk(KERN_WARNING "%s: timeout = 0x%x [type = %d:%d, " \
> +					"refcnt = %d, locked = %d]\n",
> +					sync->name, (u32)sobj->dmabuf,
> +					sobj->robj->accessed_type,
> +					sobj->access_type,
> +					atomic_read(&sobj->robj->shared_cnt),
> +					sobj->robj->locked);

pr_warn_ratelimited?

> +
> +		/* unlock only valid sync object. */
> +		if (!sobj->robj->locked) {
> +			mutex_unlock(&sobj->robj->lock);
> +			continue;
> +		}
> +
> +		if (sobj->robj->polled) {
> +			sobj->robj->poll_event = true;
> +			sobj->robj->polled = false;
> +			wake_up_interruptible(&sobj->robj->poll_wait);
> +		}
> +
> +		if (atomic_add_unless(&sobj->robj->shared_cnt, -1, 1)) {
> +			mutex_unlock(&sobj->robj->lock);
> +			continue;
> +		}
> +
> +		mutex_unlock(&sobj->robj->lock);
> +
> +		ww_mutex_unlock(&sobj->robj->sync_lock);
> +
> +		mutex_lock(&sobj->robj->lock);
> +		sobj->robj->locked = false;
> +
> +		if (sobj->access_type & DMA_BUF_ACCESS_R)
> +			printk(KERN_WARNING "%s: r-unlocked = 0x%x\n",
> +					sync->name, (u32)sobj->dmabuf);
> +		else
> +			printk(KERN_WARNING "%s: w-unlocked = 0x%x\n",
> +					sync->name, (u32)sobj->dmabuf);

How about using 'pr_warn'? And  in it have:

		sobj->access_type & DMA_BUF_ACCESS_R ? "r-" : "w-",

	and just have one printk.

Why the (u32) casting?  Don't you want %p ?

> +
> +		mutex_unlock(&sobj->robj->lock);
> +	}
> +
> +	sync->status = 0;
> +	mutex_unlock(&sync->lock);
> +
> +	dmabuf_sync_put_all(sync);
> +	dmabuf_sync_fini(sync);
> +}
> +
> +static void dmabuf_sync_lock_timeout(unsigned long arg)
> +{
> +	struct dmabuf_sync *sync = (struct dmabuf_sync *)arg;
> +
> +	schedule_work(&sync->work);
> +}
> +
> +static int dmabuf_sync_lock_objs(struct dmabuf_sync *sync,
> +					struct ww_acquire_ctx *ctx)
> +{
> +	struct dmabuf_sync_object *contended_sobj = NULL;
> +	struct dmabuf_sync_object *res_sobj = NULL;
> +	struct dmabuf_sync_object *sobj = NULL;
> +	int ret;
> +
> +	if (ctx)
> +		ww_acquire_init(ctx, &dmabuf_sync_ww_class);
> +
> +retry:
> +	list_for_each_entry(sobj, &sync->syncs, head) {
> +		if (WARN_ON(!sobj->robj))
> +			continue;
> +
> +		mutex_lock(&sobj->robj->lock);
> +
> +		/* Don't lock in case of read and read. */
> +		if (sobj->robj->accessed_type & DMA_BUF_ACCESS_R &&
> +		    sobj->access_type & DMA_BUF_ACCESS_R) {
> +			atomic_inc(&sobj->robj->shared_cnt);
> +			mutex_unlock(&sobj->robj->lock);
> +			continue;
> +		}
> +
> +		if (sobj == res_sobj) {
> +			res_sobj = NULL;
> +			mutex_unlock(&sobj->robj->lock);
> +			continue;
> +		}
> +
> +		mutex_unlock(&sobj->robj->lock);
> +
> +		ret = ww_mutex_lock(&sobj->robj->sync_lock, ctx);
> +		if (ret < 0) {
> +			contended_sobj = sobj;
> +
> +			if (ret == -EDEADLK)
> +				printk(KERN_WARNING"%s: deadlock = 0x%x\n",
> +					sync->name, (u32)sobj->dmabuf);

Again, why (u32) and not %p?

> +			goto err;

This looks odd. You jump to err, which jumps back to 'retry'. Won't this
cause an infinite loop? Perhaps you need to add a retry counter to only
do this up to five times or so and then give up?

> +		}
> +
> +		mutex_lock(&sobj->robj->lock);
> +		sobj->robj->locked = true;
> +
> +		mutex_unlock(&sobj->robj->lock);
> +	}
> +
> +	if (ctx)
> +		ww_acquire_done(ctx);
> +
> +	init_timer(&sync->timer);
> +
> +	sync->timer.data = (unsigned long)sync;
> +	sync->timer.function = dmabuf_sync_lock_timeout;
> +	sync->timer.expires = jiffies + (HZ * MAX_SYNC_TIMEOUT);
> +
> +	add_timer(&sync->timer);
> +
> +	return 0;
> +
> +err:
> +	list_for_each_entry_continue_reverse(sobj, &sync->syncs, head) {
> +		mutex_lock(&sobj->robj->lock);
> +
> +		/* Don't need to unlock in case of read and read. */
> +		if (atomic_add_unless(&sobj->robj->shared_cnt, -1, 1)) {
> +			mutex_unlock(&sobj->robj->lock);
> +			continue;
> +		}
> +
> +		ww_mutex_unlock(&sobj->robj->sync_lock);
> +		sobj->robj->locked = false;
> +
> +		mutex_unlock(&sobj->robj->lock);
> +	}
> +
> +	if (res_sobj) {
> +		mutex_lock(&res_sobj->robj->lock);
> +
> +		if (!atomic_add_unless(&res_sobj->robj->shared_cnt, -1, 1)) {
> +			ww_mutex_unlock(&res_sobj->robj->sync_lock);
> +			res_sobj->robj->locked = false;
> +		}
> +
> +		mutex_unlock(&res_sobj->robj->lock);
> +	}
> +
> +	if (ret == -EDEADLK) {
> +		ww_mutex_lock_slow(&contended_sobj->robj->sync_lock, ctx);
> +		res_sobj = contended_sobj;
> +
> +		goto retry;
> +	}
> +
> +	if (ctx)
> +		ww_acquire_fini(ctx);
> +
> +	return ret;
> +}
> +
> +static void dmabuf_sync_unlock_objs(struct dmabuf_sync *sync,
> +					struct ww_acquire_ctx *ctx)
> +{
> +	struct dmabuf_sync_object *sobj;
> +
> +	if (list_empty(&sync->syncs))
> +		return;
> +
> +	mutex_lock(&sync->lock);
> +
> +	list_for_each_entry(sobj, &sync->syncs, head) {
> +		mutex_lock(&sobj->robj->lock);
> +
> +		if (sobj->robj->polled) {
> +			sobj->robj->poll_event = true;
> +			sobj->robj->polled = false;
> +			wake_up_interruptible(&sobj->robj->poll_wait);
> +		}
> +
> +		if (atomic_add_unless(&sobj->robj->shared_cnt, -1, 1)) {
> +			mutex_unlock(&sobj->robj->lock);
> +			continue;
> +		}
> +
> +		mutex_unlock(&sobj->robj->lock);
> +
> +		ww_mutex_unlock(&sobj->robj->sync_lock);
> +
> +		mutex_lock(&sobj->robj->lock);
> +		sobj->robj->locked = false;
> +		mutex_unlock(&sobj->robj->lock);
> +	}
> +
> +	mutex_unlock(&sync->lock);
> +
> +	if (ctx)
> +		ww_acquire_fini(ctx);
> +
> +	del_timer(&sync->timer);
> +}
> +
> +/**
> + * is_dmabuf_sync_supported - Check if dmabuf sync is supported or not.
> + */
> +bool is_dmabuf_sync_supported(void)
> +{
> +	return dmabuf_sync_enabled == 1;
> +}
> +EXPORT_SYMBOL(is_dmabuf_sync_supported);

_GPL ?

I would also prefix it with 'dmabuf_is_sync_supported' just to make
all of the libraries call start with 'dmabuf'

> +
> +/**
> + * dmabuf_sync_init - Allocate and initialize a dmabuf sync.
> + *
> + * @priv: A device private data.
> + * @name: A sync object name.
> + *
> + * This function should be called when a device context or an event
> + * context such as a page flip event is created. And the created
> + * dmabuf_sync object should be set to the context.
> + * The caller can get a new sync object for buffer synchronization
> + * through this function.
> + */
> +struct dmabuf_sync *dmabuf_sync_init(const char *name,
> +					struct dmabuf_sync_priv_ops *ops,
> +					void *priv)
> +{
> +	struct dmabuf_sync *sync;
> +
> +	sync = kzalloc(sizeof(*sync), GFP_KERNEL);
> +	if (!sync)
> +		return ERR_PTR(-ENOMEM);
> +
> +	strncpy(sync->name, name, ARRAY_SIZE(sync->name) - 1);
> +

That is odd usage of an ARRAY_SIZE, but I can see how you can use it.
I would say you should just do a #define for the 64 line and use that
instead.

> +	sync->ops = ops;
> +	sync->priv = priv;
> +	INIT_LIST_HEAD(&sync->syncs);
> +	mutex_init(&sync->lock);
> +	INIT_WORK(&sync->work, dmabuf_sync_timeout_worker);
> +
> +	return sync;
> +}
> +EXPORT_SYMBOL(dmabuf_sync_init);

_GPL ?
> +
> +/**
> + * dmabuf_sync_fini - Release a given dmabuf sync.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + *
> + * This function should be called if some operation is failed after
> + * dmabuf_sync_init call to release relevant resources, and after
> + * dmabuf_sync_unlock function is called.
> + */
> +void dmabuf_sync_fini(struct dmabuf_sync *sync)
> +{
> +	if (WARN_ON(!sync))
> +		return;
> +
> +	if (sync->ops && sync->ops->free)
> +		sync->ops->free(sync->priv);
> +

No need to cancel the sync->work in case that is still
running?

> +	kfree(sync);
> +}
> +EXPORT_SYMBOL(dmabuf_sync_fini);

_GPL ?
> +
> +/*
> + * dmabuf_sync_get_obj - Add a given object to syncs list.

sync's list I think?

> + *
> + * @sync: An object to dmabuf_sync structure.
> + * @dmabuf: An object to dma_buf structure.
> + * @type: A access type to a dma buf.
> + *	The DMA_BUF_ACCESS_R means that this dmabuf could be accessed by
> + *	others for read access. On the other hand, the DMA_BUF_ACCESS_W
> + *	means that this dmabuf couldn't be accessed by others but would be
> + *	accessed by caller's dma exclusively. And the DMA_BUF_ACCESS_DMA can be
> + *	combined.

Should this be an enum?
> + *
> + * This function creates and initializes a new dmabuf sync object and it adds
> + * the dmabuf sync object to syncs list to track and manage all dmabufs.
> + */
> +static int dmabuf_sync_get_obj(struct dmabuf_sync *sync, struct dma_buf *dmabuf,
> +					unsigned int type)

enum for 'type'?
> +{
> +	struct dmabuf_sync_object *sobj;
> +
> +	if (!dmabuf->sync) {
> +		WARN_ON(1);
> +		return -EFAULT;
> +	}
> +
> +	if (!IS_VALID_DMA_BUF_ACCESS_TYPE(type))
> +		return -EINVAL;
> +
> +	if ((type & DMA_BUF_ACCESS_RW) == DMA_BUF_ACCESS_RW)
> +		type &= ~DMA_BUF_ACCESS_R;

Ah, that is why you are not using an enum.

> +
> +	sobj = kzalloc(sizeof(*sobj), GFP_KERNEL);
> +	if (!sobj) {
> +		WARN_ON(1);

I think you can skip that WARN_ON. Handling an -ENOMEM should be
something fairly easy to handle by the calleer.

> +		return -ENOMEM;
> +	}
> +
> +	get_dma_buf(dmabuf);
> +
> +	sobj->dmabuf = dmabuf;
> +	sobj->robj = dmabuf->sync;
> +	sobj->access_type = type;
> +
> +	mutex_lock(&sync->lock);
> +	list_add_tail(&sobj->head, &sync->syncs);
> +	mutex_unlock(&sync->lock);
> +
> +	return 0;
> +}
> +
> +/*
> + * dmabuf_sync_put_obj - Release a given sync object.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + *
> + * This function should be called if some operation is failed after

s/is//
> + * dmabuf_sync_get_obj call to release a given sync object.
> + */
> +static void dmabuf_sync_put_obj(struct dmabuf_sync *sync,
> +					struct dma_buf *dmabuf)
> +{
> +	struct dmabuf_sync_object *sobj;
> +
> +	mutex_lock(&sync->lock);
> +
> +	list_for_each_entry(sobj, &sync->syncs, head) {
> +		if (sobj->dmabuf != dmabuf)
> +			continue;
> +
> +		dma_buf_put(sobj->dmabuf);
> +
> +		list_del_init(&sobj->head);
> +		kfree(sobj);
> +		break;
> +	}
> +
> +	if (list_empty(&sync->syncs))
> +		sync->status = 0;
> +
> +	mutex_unlock(&sync->lock);
> +}
> +
> +/*
> + * dmabuf_sync_put_objs - Release all sync objects of dmabuf_sync.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + *
> + * This function should be called if some operation is failed after

s/is//

> + * dmabuf_sync_get_obj call to release all sync objects.
> + */
> +static void dmabuf_sync_put_objs(struct dmabuf_sync *sync)
> +{
> +	struct dmabuf_sync_object *sobj, *next;
> +
> +	mutex_lock(&sync->lock);
> +
> +	list_for_each_entry_safe(sobj, next, &sync->syncs, head) {
> +		dma_buf_put(sobj->dmabuf);
> +
> +		list_del_init(&sobj->head);
> +		kfree(sobj);
> +	}
> +
> +	mutex_unlock(&sync->lock);
> +
> +	sync->status = 0;
> +}
> +
> +/**
> + * dmabuf_sync_lock - lock all dmabufs added to syncs list.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + *
> + * The caller should call this function prior to CPU or DMA access to
> + * the dmabufs so that others can not access the dmabufs.
> + * Internally, this function avoids dead lock issue with ww-mutex.
> + */
> +int dmabuf_sync_lock(struct dmabuf_sync *sync)
> +{
> +	int ret;
> +
> +	if (!sync) {
> +		WARN_ON(1);
> +		return -EFAULT;
> +	}
> +
> +	if (list_empty(&sync->syncs))
> +		return -EINVAL;
> +
> +	if (sync->status != DMABUF_SYNC_GOT)
> +		return -EINVAL;
> +
> +	ret = dmabuf_sync_lock_objs(sync, &sync->ctx);
> +	if (ret < 0) {
> +		WARN_ON(1);

Perhaps also include the ret value in the WARN?

> +		return ret;
> +	}
> +
> +	sync->status = DMABUF_SYNC_LOCKED;
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(dmabuf_sync_lock);

I think you know what I am going to say.
> +
> +/**
> + * dmabuf_sync_unlock - unlock all objects added to syncs list.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + *
> + * The caller should call this function after CPU or DMA access to
> + * the dmabufs is completed so that others can access the dmabufs.
> + */
> +int dmabuf_sync_unlock(struct dmabuf_sync *sync)
> +{
> +	if (!sync) {
> +		WARN_ON(1);
> +		return -EFAULT;
> +	}
> +
> +	/* If current dmabuf sync object wasn't reserved then just return. */
> +	if (sync->status != DMABUF_SYNC_LOCKED)
> +		return -EAGAIN;
> +
> +	dmabuf_sync_unlock_objs(sync, &sync->ctx);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(dmabuf_sync_unlock);
> +
> +/**
> + * dmabuf_sync_single_lock - lock a dma buf.
> + *
> + * @dmabuf: A dma buf object that tries to lock.
> + * @type: A access type to a dma buf.
> + *	The DMA_BUF_ACCESS_R means that this dmabuf could be accessed by
> + *	others for read access. On the other hand, the DMA_BUF_ACCESS_W
> + *	means that this dmabuf couldn't be accessed by others but would be
> + *	accessed by caller's dma exclusively. And the DMA_BUF_ACCESS_DMA can
> + *	be combined with other.
> + * @wait: Indicate whether caller is blocked or not.
> + *	true means that caller will be blocked, and false means that this
> + *	function will return -EAGAIN if this caller can't take the lock
> + *	right now.
> + *
> + * The caller should call this function prior to CPU or DMA access to the dmabuf
> + * so that others cannot access the dmabuf.
> + */
> +int dmabuf_sync_single_lock(struct dma_buf *dmabuf, unsigned int type,
> +				bool wait)
> +{
> +	struct dmabuf_sync_reservation *robj;
> +
> +	if (!dmabuf->sync) {
> +		WARN_ON(1);
> +		return -EFAULT;
> +	}
> +
> +	if (!IS_VALID_DMA_BUF_ACCESS_TYPE(type)) {
> +		WARN_ON(1);
> +		return -EINVAL;
> +	}
> +
> +	get_dma_buf(dmabuf);
> +	robj = dmabuf->sync;
> +
> +	mutex_lock(&robj->lock);
> +
> +	/* Don't lock in case of read and read. */
> +	if (robj->accessed_type & DMA_BUF_ACCESS_R && type & DMA_BUF_ACCESS_R) {
> +		atomic_inc(&robj->shared_cnt);
> +		mutex_unlock(&robj->lock);
> +		return 0;
> +	}
> +
> +	/*
> +	 * In case of F_SETLK, just return -EAGAIN if this dmabuf has already
> +	 * been locked.
> +	 */
> +	if (!wait && robj->locked) {
> +		mutex_unlock(&robj->lock);
> +		dma_buf_put(dmabuf);
> +		return -EAGAIN;
> +	}
> +
> +	mutex_unlock(&robj->lock);
> +
> +	mutex_lock(&robj->sync_lock.base);
> +
> +	mutex_lock(&robj->lock);
> +	robj->locked = true;
> +	mutex_unlock(&robj->lock);

Are you missing an mutex_unlock on &robj->sync_lock.base?
Oh wait, that is the purpose of this code. You might want
to put a nice comment right above that and say: "Unlocked
by dmabuf_sync_single_unlock"

> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(dmabuf_sync_single_lock);
> +
> +/**
> + * dmabuf_sync_single_unlock - unlock a dma buf.
> + *
> + * @dmabuf: A dma buf object that tries to unlock.
> + *
> + * The caller should call this function after CPU or DMA access to
> + * the dmabuf is completed so that others can access the dmabuf.
> + */
> +void dmabuf_sync_single_unlock(struct dma_buf *dmabuf)
> +{
> +	struct dmabuf_sync_reservation *robj;
> +
> +	if (!dmabuf->sync) {
> +		WARN_ON(1);
> +		return;
> +	}
> +
> +	robj = dmabuf->sync;
> +
> +	mutex_lock(&robj->lock);
> +
> +	if (robj->polled) {
> +		robj->poll_event = true;
> +		robj->polled = false;
> +		wake_up_interruptible(&robj->poll_wait);
> +	}
> +
> +	if (atomic_add_unless(&robj->shared_cnt, -1 , 1)) {
> +		mutex_unlock(&robj->lock);
> +		dma_buf_put(dmabuf);
> +		return;
> +	}
> +
> +	mutex_unlock(&robj->lock);
> +
> +	mutex_unlock(&robj->sync_lock.base);
> +
> +	mutex_lock(&robj->lock);
> +	robj->locked = false;
> +	mutex_unlock(&robj->lock);
> +
> +	dma_buf_put(dmabuf);
> +
> +	return;
> +}
> +EXPORT_SYMBOL(dmabuf_sync_single_unlock);
> +
> +/**
> + * dmabuf_sync_get - Get dmabuf sync object.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + * @sync_buf: A dmabuf object to be synchronized with others.
> + * @type: A access type to a dma buf.
> + *	The DMA_BUF_ACCESS_R means that this dmabuf could be accessed by
> + *	others for read access. On the other hand, the DMA_BUF_ACCESS_W
> + *	means that this dmabuf couldn't be accessed by others but would be
> + *	accessed by caller's dma exclusively. And the DMA_BUF_ACCESS_DMA can
> + *	be combined with other.
> + *
> + * This function should be called after dmabuf_sync_init function is called.
> + * The caller can tie up multiple dmabufs into one sync object by calling this
> + * function several times. Internally, this function allocates
> + * a dmabuf_sync_object and adds a given dmabuf to it, and also takes
> + * a reference to a dmabuf.
> + */
> +int dmabuf_sync_get(struct dmabuf_sync *sync, void *sync_buf, unsigned int type)
> +{
> +	int ret;
> +
> +	if (!sync || !sync_buf) {
> +		WARN_ON(1);
> +		return -EFAULT;
> +	}
> +
> +	ret = dmabuf_sync_get_obj(sync, sync_buf, type);
> +	if (ret < 0) {
> +		WARN_ON(1);
> +		return ret;
> +	}
> +
> +	sync->status = DMABUF_SYNC_GOT;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(dmabuf_sync_get);
> +
> +/**
> + * dmabuf_sync_put - Put dmabuf sync object to a given dmabuf.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + * @dmabuf: An dmabuf object.
> + *
> + * This function should be called if some operation is failed after
> + * dmabuf_sync_get function is called to release the dmabuf, or
> + * dmabuf_sync_unlock function is called. Internally, this function
> + * removes a given dmabuf from a sync object and remove the sync object.
> + * At this time, the dmabuf is putted.
> + */
> +void dmabuf_sync_put(struct dmabuf_sync *sync, struct dma_buf *dmabuf)
> +{
> +	if (!sync || !dmabuf) {
> +		WARN_ON(1);
> +		return;
> +	}
> +
> +	if (list_empty(&sync->syncs))
> +		return;
> +
> +	dmabuf_sync_put_obj(sync, dmabuf);
> +}
> +EXPORT_SYMBOL(dmabuf_sync_put);
> +
> +/**
> + * dmabuf_sync_put_all - Put dmabuf sync object to dmabufs.
> + *
> + * @sync: An object to dmabuf_sync structure.
> + *
> + * This function should be called if some operation is failed after
> + * dmabuf_sync_get function is called to release all sync objects, or
> + * dmabuf_sync_unlock function is called. Internally, this function
> + * removes dmabufs from a sync object and remove the sync object.
> + * At this time, all dmabufs are putted.
> + */
> +void dmabuf_sync_put_all(struct dmabuf_sync *sync)
> +{
> +	if (!sync) {
> +		WARN_ON(1);
> +		return;
> +	}
> +
> +	if (list_empty(&sync->syncs))
> +		return;
> +
> +	dmabuf_sync_put_objs(sync);
> +}
> +EXPORT_SYMBOL(dmabuf_sync_put_all);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index dfac5ed..0109673 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -115,6 +115,7 @@ struct dma_buf_ops {
>   * @exp_name: name of the exporter; useful for debugging.
>   * @list_node: node for dma_buf accounting and debugging.
>   * @priv: exporter specific private data for this buffer object.
> + * @sync: sync object linked to this dma-buf
>   */
>  struct dma_buf {
>  	size_t size;
> @@ -128,6 +129,7 @@ struct dma_buf {
>  	const char *exp_name;
>  	struct list_head list_node;
>  	void *priv;
> +	void *sync;
>  };
>  
>  /**
> @@ -148,6 +150,20 @@ struct dma_buf_attachment {
>  	void *priv;
>  };
>  
> +#define	DMA_BUF_ACCESS_R	0x1
> +#define DMA_BUF_ACCESS_W	0x2
> +#define DMA_BUF_ACCESS_DMA	0x4
> +#define DMA_BUF_ACCESS_RW	(DMA_BUF_ACCESS_R | DMA_BUF_ACCESS_W)
> +#define DMA_BUF_ACCESS_DMA_R	(DMA_BUF_ACCESS_R | DMA_BUF_ACCESS_DMA)
> +#define DMA_BUF_ACCESS_DMA_W	(DMA_BUF_ACCESS_W | DMA_BUF_ACCESS_DMA)
> +#define DMA_BUF_ACCESS_DMA_RW	(DMA_BUF_ACCESS_DMA_R | DMA_BUF_ACCESS_DMA_W)
> +#define IS_VALID_DMA_BUF_ACCESS_TYPE(t)	(t == DMA_BUF_ACCESS_R || \
> +					 t == DMA_BUF_ACCESS_W || \
> +					 t == DMA_BUF_ACCESS_DMA_R || \
> +					 t == DMA_BUF_ACCESS_DMA_W || \
> +					 t == DMA_BUF_ACCESS_RW || \
> +					 t == DMA_BUF_ACCESS_DMA_RW)
> +
>  /**
>   * get_dma_buf - convenience wrapper for get_file.
>   * @dmabuf:	[in]	pointer to dma_buf
> diff --git a/include/linux/dmabuf-sync.h b/include/linux/dmabuf-sync.h
> new file mode 100644
> index 0000000..9a3afc4
> --- /dev/null
> +++ b/include/linux/dmabuf-sync.h
> @@ -0,0 +1,190 @@
> +/*
> + * Copyright (C) 2013 Samsung Electronics Co.Ltd
> + * Authors:
> + *	Inki Dae <[email-masked]>
> + *
> + * This program is free software; you can redistribute  it and/or modify it
> + * under  the terms of  the GNU General  Public License as published by the
> + * Free Software Foundation;  either version 2 of the  License, or (at your
> + * option) any later version.
> + *
> + */
> +
> +#include <linux/mutex.h>
> +#include <linux/sched.h>
> +#include <linux/dma-buf.h>
> +
> +enum dmabuf_sync_status {
> +	DMABUF_SYNC_GOT		= 1,
> +	DMABUF_SYNC_LOCKED,
> +};
> +

No comment about this structure?

> +struct dmabuf_sync_reservation {
> +	struct ww_mutex		sync_lock;
> +	struct mutex		lock;
> +	wait_queue_head_t	poll_wait;
> +	unsigned int		poll_event;
> +	unsigned int		polled;
> +	atomic_t		shared_cnt;
> +	unsigned int		accessed_type;
> +	unsigned int		locked;
> +};
> +
> +/*
> + * A structure for dmabuf_sync_object.
> + *
> + * @head: A list head to be added to syncs list.
> + * @robj: A reservation_object object.
> + * @dma_buf: A dma_buf object.
> + * @access_type: Indicate how a current task tries to access
> + *	a given buffer.

Huh? What values are expected then? Is there some #define or enum
for that?

> + */
> +struct dmabuf_sync_object {
> +	struct list_head		head;
> +	struct dmabuf_sync_reservation	*robj;
> +	struct dma_buf			*dmabuf;
> +	unsigned int			access_type;
> +};
> +
> +struct dmabuf_sync_priv_ops {
> +	void (*free)(void *priv);
> +};
> +
> +/*
> + * A structure for dmabuf_sync.
> + *
> + * @syncs: A list head to sync object and this is global to system.
> + * @list: A list entry used as committed list node
> + * @lock: A mutex lock to current sync object.

You should say for which specific operations this mutex is needed.
For everything? Or just for list operations.

> + * @ctx: A current context for ww mutex.
> + * @work: A work struct to release resources at timeout.
> + * @priv: A private data.
> + * @name: A string to dmabuf sync owner.
> + * @timer: A timer list to avoid lockup and release resources.
> + * @status: Indicate current status (DMABUF_SYNC_GOT or DMABUF_SYNC_LOCKED).
> + */
> +struct dmabuf_sync {
> +	struct list_head		syncs;
> +	struct list_head		list;
> +	struct mutex			lock;
> +	struct ww_acquire_ctx		ctx;
> +	struct work_struct		work;
> +	void				*priv;
> +	struct dmabuf_sync_priv_ops	*ops;
> +	char				name[64];

Perhaps a #define for the size?

> +	struct timer_list		timer;
> +	unsigned int			status;
> +};
> +
> +#ifdef CONFIG_DMABUF_SYNC
> +
> +extern struct ww_class dmabuf_sync_ww_class;
> +
> +static inline void dmabuf_sync_reservation_init(struct dma_buf *dmabuf)
> +{
> +	struct dmabuf_sync_reservation *obj;
> +
> +	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> +	if (!obj)
> +		return;
> +
> +	dmabuf->sync = obj;
> +
> +	ww_mutex_init(&obj->sync_lock, &dmabuf_sync_ww_class);
> +
> +	mutex_init(&obj->lock);
> +	atomic_set(&obj->shared_cnt, 1);
> +
> +	init_waitqueue_head(&obj->poll_wait);
> +}
> +
> +static inline void dmabuf_sync_reservation_fini(struct dma_buf *dmabuf)
> +{
> +	struct dmabuf_sync_reservation *obj;
> +
> +	if (!dmabuf->sync)
> +		return;
> +
> +	obj = dmabuf->sync;
> +
> +	ww_mutex_destroy(&obj->sync_lock);
> +
> +	kfree(obj);
> +}
> +
> +extern bool is_dmabuf_sync_supported(void);
> +
> +extern struct dmabuf_sync *dmabuf_sync_init(const char *name,
> +					struct dmabuf_sync_priv_ops *ops,
> +					void *priv);
> +
> +extern void dmabuf_sync_fini(struct dmabuf_sync *sync);
> +
> +extern int dmabuf_sync_lock(struct dmabuf_sync *sync);
> +
> +extern int dmabuf_sync_unlock(struct dmabuf_sync *sync);
> +
> +int dmabuf_sync_single_lock(struct dma_buf *dmabuf, unsigned int type,
> +				bool wait);
> +
> +void dmabuf_sync_single_unlock(struct dma_buf *dmabuf);
> +
> +extern int dmabuf_sync_get(struct dmabuf_sync *sync, void *sync_buf,
> +				unsigned int type);
> +
> +extern void dmabuf_sync_put(struct dmabuf_sync *sync, struct dma_buf *dmabuf);
> +
> +extern void dmabuf_sync_put_all(struct dmabuf_sync *sync);
> +
> +#else
> +
> +static inline void dmabuf_sync_reservation_init(struct dma_buf *dmabuf) { }
> +
> +static inline void dmabuf_sync_reservation_fini(struct dma_buf *dmabuf) { }
> +
> +static inline bool is_dmabuf_sync_supported(void) { return false; }
> +
> +static inline  struct dmabuf_sync *dmabuf_sync_init(const char *name,
> +					struct dmabuf_sync_priv_ops *ops,
> +					void *priv)
> +{
> +	return ERR_PTR(0);
> +}
> +
> +static inline void dmabuf_sync_fini(struct dmabuf_sync *sync) { }
> +
> +static inline int dmabuf_sync_lock(struct dmabuf_sync *sync)
> +{
> +	return 0;
> +}
> +
> +static inline int dmabuf_sync_unlock(struct dmabuf_sync *sync)
> +{
> +	return 0;
> +}
> +
> +static inline int dmabuf_sync_single_lock(struct dma_buf *dmabuf,
> +						unsigned int type,
> +						bool wait)
> +{
> +	return 0;
> +}
> +
> +static inline void dmabuf_sync_single_unlock(struct dma_buf *dmabuf)
> +{
> +	return;
> +}
> +
> +static inline int dmabuf_sync_get(struct dmabuf_sync *sync,
> +					void *sync_buf,
> +					unsigned int type)
> +{
> +	return 0;
> +}
> +
> +static inline void dmabuf_sync_put(struct dmabuf_sync *sync,
> +					struct dma_buf *dmabuf) { }
> +
> +static inline void dmabuf_sync_put_all(struct dmabuf_sync *sync) { }
> +
> +#endif
> -- 
> 1.7.5.4
> 
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