Subject: [PATCH] of: Add generic device tree DMA helpers

From: [email-masked] (Grant Likely)
Date: Sat, 17 Mar 2012 09:40:59 +0000

On Thu, 15 Mar 2012 09:38:10 +0100, Nicolas Ferre <[email-masked]> wrote:
> Add some basic helpers to retrieve a DMA controller device_node and the
> DMA request specifications. By making DMA controllers register a generic
> translation function, we allow the management of any type of DMA requests
> specification.
> The void * output of an of_dma_xlate() function that will be implemented
> by the DMA controller can carry any type of "dma-request" argument.
> 
> The DMA client will search its associated DMA controller in the list and
> call the registered of_dam_xlate() function to retrieve the request values.
> 
> One simple xlate function is provided for the "single number" type of
> request binding.
> 
> This implementation is independent from dmaengine so it can also be used
> by legacy drivers.
> 
> For legacy reason another API will export the DMA request number into a
> Linux resource of type IORESOURCE_DMA.
> 
> Signed-off-by: Nicolas Ferre <[email-masked]>
> Signed-off-by: Benoit Cousson <[email-masked]>

Hi Nicolas,

Comments below.

> Cc: Stephen Warren <[email-masked]>
> Cc: Grant Likely <[email-masked]>
> Cc: Russell King <[email-masked]>
> Cc: Rob Herring <[email-masked]>
> ---
>  Documentation/devicetree/bindings/dma/dma.txt |   45 +++++
>  drivers/of/Kconfig                            |    5 +
>  drivers/of/Makefile                           |    1 +
>  drivers/of/dma.c                              |  260 +++++++++++++++++++++++++
>  include/linux/of_dma.h                        |   67 +++++++
>  5 files changed, 378 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/dma/dma.txt
>  create mode 100644 drivers/of/dma.c
>  create mode 100644 include/linux/of_dma.h
> 
> diff --git a/Documentation/devicetree/bindings/dma/dma.txt b/Documentation/devicetree/bindings/dma/dma.txt
> new file mode 100644
> index 0000000..c49e98d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/dma.txt
> @@ -0,0 +1,45 @@
> +* Generic DMA Controller and DMA request bindings
> +
> +Generic binding to provide a way for a driver to retrieve the
> +DMA request line that goes from an IP to a DMA controller.
> +
> +
> +* DMA controller
> +
> +Required property:
> +    - #dma-cells: Number of cells for each DMA line.
> +
> +
> +Example:
> +
> +	sdma: dma-controller at 48000000 {
> +		compatible = "ti,sdma-omap4"
> +		reg = <0x48000000 0x1000>;
> +		interrupts = <12>;
> +		#dma-cells = <1>;
> +	};
> +
> +
> +
> +* DMA client
> +
> +Client drivers should specify the DMA request property using a phandle to
> +the controller. If needed, the DMA request identity on that controller is then
> +added followed by optional request specifications.
> +
> +Required property:
> +    - dma-request: List of phandle + dma-request + request specifications,
> +      one group per request "line".
> +Optional property:
> +    - dma-request-names: list of strings in the same order as the dma-request
> +      in the dma-request property.
> +
> +
> +Example:
> +
> +	i2c1: i2c at 1 {
> +		...
> +		dma-request = <&sdma 2 &sdma 3>;
> +		dma-request-names = "tx", "rx";
> +		...
> +	};
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index 268163d..7d1f06b 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -90,4 +90,9 @@ config OF_PCI_IRQ
>  	help
>  	  OpenFirmware PCI IRQ routing helpers
>  
> +config OF_DMA
> +	def_bool y
> +	help
> +	  Device Tree DMA routing helpers

Not really any point in having this config symbol at all if it is
always enabled.

> +
>  endmenu # OF
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index a73f5a5..6eb50c6 100644
> --- a/drivers/of/Makefile
> +++ b/drivers/of/Makefile
> @@ -12,3 +12,4 @@ obj-$(CONFIG_OF_SELFTEST) += selftest.o
>  obj-$(CONFIG_OF_MDIO)	+= of_mdio.o
>  obj-$(CONFIG_OF_PCI)	+= of_pci.o
>  obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
> +obj-$(CONFIG_OF_DMA)	+= dma.o
> diff --git a/drivers/of/dma.c b/drivers/of/dma.c
> new file mode 100644
> index 0000000..3315844
> --- /dev/null
> +++ b/drivers/of/dma.c
> @@ -0,0 +1,260 @@
> +/*
> + * Device tree helpers for DMA request / controller
> + *
> + * Based on of_gpio.c
> + *
> + * Copyright (C) 2012 Texas Instruments Incorporated - http://www.ti.com/
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/module.h>
> +#include <linux/rculist.h>
> +#include <linux/slab.h>
> +#include <linux/of.h>
> +#include <linux/of_dma.h>
> +
> +static LIST_HEAD(of_dma_list);
> +
> +struct of_dma {
> +	struct list_head of_dma_controllers;
> +	struct device_node *of_node;
> +	int of_dma_n_cells;
> +	int (*of_dma_xlate)(struct of_phandle_args *dma_spec, void *data);
> +};

This _xlate is nearly useless as a generic API.  It solves the problem for
the specific case where the driver is hard-coded to know which DMA engine
to talk to, but since the returned data doesn't provide any context, it
isn't useful if there are multiple DMA controllers to choose from.

The void *data pointer must be replaced with a typed structure so that
context can be returned.

> +
> +/**
> + * of_dma_find_controller() - Find a DMA controller in DT DMA helpers list
> + * @np:		device node of DMA controller
> + */
> +static struct of_dma *of_dma_find_controller(struct device_node *np)
> +{
> +	struct of_dma	*ofdma;
> +
> +	list_for_each_entry_rcu(ofdma, &of_dma_list, of_dma_controllers) {
> +		if (ofdma->of_node == np)
> +			return ofdma;
> +	}
> +
> +	return NULL;
> +}
> +
> +/**
> + * of_dma_controller_register() - Register a DMA controller to DT DMA helpers
> + * @np:			device node of DMA controller
> + * @of_dma_xlate:	generic translation function which converts a phandle
> + *			arguments list into a generic output value
> + *
> + * Returns 0 on success or appropriate errno value on error.
> + *
> + * If #dma-cells is not specified in DMA controller device tree node, we assume
> + * that the DMA controller phandle will come without argument.
> + *
> + * Allocated memory should be freed with appropriate of_dma_controller_free()
> + * call.
> + */
> +int of_dma_controller_register(struct device_node *np,
> +			int (*of_dma_xlate)(struct of_phandle_args *, void *))
> +{
> +	struct of_dma	*ofdma;
> +	const __be32	*nbcells;
> +
> +	if (!np || !of_dma_xlate) {
> +		pr_err("%s: not enough information provided\n", __func__);
> +		return -EINVAL;
> +	}
> +
> +	ofdma = kzalloc(sizeof(*ofdma), GFP_KERNEL);
> +	if (!ofdma)
> +		return -ENOMEM;
> +
> +	nbcells = of_get_property(np, "#dma-cells", NULL);
> +	if (!nbcells)
> +		/*
> +		 * no #dma-cells properties: assume no argument to
> +		 * dma-request property on slave side
> +		 */
> +		ofdma->of_dma_n_cells = 0;
> +	else
> +		ofdma->of_dma_n_cells = be32_to_cpup(nbcells);

Make #dma-cells a required property

> +
> +	ofdma->of_node = np;
> +	ofdma->of_dma_xlate = of_dma_xlate;
> +
> +	/* Now queue of_dma controller structure in list */
> +	list_add_tail_rcu(&ofdma->of_dma_controllers, &of_dma_list);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_dma_controller_register);
> +
> +/**
> + * of_dma_controller_free() - Remove a DMA controller from DT DMA helpers list
> + * @np:		device node of DMA controller
> + *
> + * Memory allocated by of_dma_controller_register() is freed here.
> + */
> +void of_dma_controller_free(struct device_node *np)
> +{
> +	struct of_dma	*ofdma;
> +
> +	ofdma = of_dma_find_controller(np);
> +	if (ofdma) {
> +		list_del_rcu(&ofdma->of_dma_controllers);
> +		kfree(ofdma);
> +	}
> +}
> +EXPORT_SYMBOL_GPL(of_dma_controller_free);
> +
> +/**
> + * of_get_dma_request() - Get the associated DMA request data
> + * @np:		device node to get DMA request from
> + * @index:	index of the DMA request
> + * @out_data:	a output that can be filled in by the of_dma_xlate() function
> + *
> + * Returns return value of of_dma_xlate() and fills out_data (if provided).
> + * On error returns the appropriate errno value.
> + */
> +int of_get_dma_request(struct device_node *np, int index,
> +		       void *out_data)
> +{
> +	struct of_phandle_args	dma_spec;
> +	struct of_dma		*ofdma;
> +	int			ret;
> +
> +	ret = of_parse_phandle_with_args(np, "dma-request", "#dma-cells",
> +					 index, &dma_spec);
> +	if (ret) {
> +		pr_err("%s: can't parse dma property\n", np->full_name);
> +		goto err0;
> +	}
> +
> +	if (list_empty(&of_dma_list)) {
> +		pr_debug("%s: empty DMA controller list\n",
> +			 np->full_name);
> +		ret = -ENOENT;
> +		goto err1;
> +	}
> +
> +	ofdma = of_dma_find_controller(dma_spec.np);
> +	if (!ofdma) {
> +		pr_debug("%s: DMA controller %s isn't registered\n",
> +			 np->full_name, dma_spec.np->full_name);
> +		ret = -ENODEV;
> +		goto err1;
> +	}
> +
> +	if (dma_spec.args_count != ofdma->of_dma_n_cells) {
> +		pr_debug("%s: wrong #dma-cells for %s\n",
> +			 np->full_name, dma_spec.np->full_name);
> +		ret = -EINVAL;
> +		goto err1;
> +	}
> +
> +	ret = ofdma->of_dma_xlate(&dma_spec, out_data);
> +
> +err1:
> +	of_node_put(dma_spec.np);
> +err0:
> +	pr_debug("%s exited with status %d\n", __func__, ret);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(of_get_dma_request);
> +
> +/**
> + * of_dma_xlate_onenumbercell() - Generic DMA xlate for direct one cell bindings
> + *
> + * Device Tree DMA translation function which works with one cell bindings
> + * where the cell values map directly to the hardware request number understood
> + * by the DMA controller.
> + */
> +int of_dma_xlate_onenumbercell(struct of_phandle_args *dma_spec, void *dma_req)
> +{
> +	if (!dma_spec)
> +		return -EINVAL;
> +	if (WARN_ON(dma_spec->args_count != 1))
> +		return -EINVAL;
> +	*(int *)dma_req = dma_spec->args[0];

Following on from comment above; the void *dma_req parameter is dangerous.  How
does this function know that it has been passed an int* pointer?

> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(of_dma_xlate_onenumbercell);
> +
> +/**
> + * of_dma_count - Count DMA requests for a device
> + * @np:		device node to count DMAs for
> + *
> + * The function returns the count of DMA requests specified for a node.
> + *
> + * Note that the empty DMA specifiers counts too. For example,
> + *
> + * dma-request = <0
> + *                &sdma 1
> + *                0
> + *                &sdma 3>;
> + *
> + * defines four DMAs (so this function will return 4), two of which
> + * are not specified.
> + */
> +unsigned int of_dma_count(struct device_node *np)
> +{
> +	unsigned int cnt = 0;
> +
> +	do {
> +		int ret;
> +
> +		ret = of_parse_phandle_with_args(np, "dma-request",
> +						 "#dma-cells", cnt, NULL);
> +		/* A hole in the dma-request = <> counts anyway. */
> +		if (ret < 0 && ret != -EEXIST)
> +			break;
> +	} while (++cnt);
> +
> +	return cnt;
> +}
> +EXPORT_SYMBOL_GPL(of_dma_count);
> +
> +/**
> + * of_dma_to_resource - Decode a node's DMA and return it as a resource
> + * @dev: pointer to device tree node
> + * @index: zero-based index of the DMA request
> + * @r: pointer to resource structure to return result into.
> + *
> + * Using a resource to export a DMA request number to a driver should
> + * be used only for legacy purpose and on system when only one DMA controller
> + * is present.
> + * The proper and only scalable way is to use the native of_get_dma_request API
> + * in order retrieve both the DMA controller device node and the DMA request
> + * line for that controller.
> + */
> +int of_dma_to_resource(struct device_node *dev, int index, struct resource *r)
> +{
> +	const char *name = NULL;
> +	int dma;
> +	int ret;
> +
> +	if (!r)
> +		return -EINVAL;
> +
> +	ret = of_get_dma_request(dev, index, &dma);
> +	if (ret < 0)
> +		return ret;
> +
> +	/*
> +	 * Get optional "dma-request-names" property to add a name
> +	 * to the resource.
> +	 */
> +	of_property_read_string_index(dev, "dma-request-names", index,
> +				      &name);
> +
> +	r->start = dma;
> +	r->end = dma;
> +	r->flags = IORESOURCE_DMA;
> +	r->name = name ? name : dev->full_name;

I'll reiterate my concern here.  The dual meaning of r->name depending
on the presence of a dma-request-names property is a real problem.  I know
this patch set hasn't introduced the problem since it already exists for
register regions and irqs, but it is expanding it.

> +
> +	return dma;
> +}
> +EXPORT_SYMBOL_GPL(of_dma_to_resource);
> diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
> new file mode 100644
> index 0000000..c6147bb
> --- /dev/null
> +++ b/include/linux/of_dma.h
> @@ -0,0 +1,67 @@
> +/*
> + * OF helpers for DMA request / controller
> + *
> + * Based on of_gpio.h
> + *
> + * Copyright (C) 2012 Texas Instruments Incorporated - http://www.ti.com/
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#ifndef __LINUX_OF_DMA_H
> +#define __LINUX_OF_DMA_H
> +
> +#include <linux/of.h>
> +
> +struct device_node;
> +
> +#ifdef CONFIG_OF_DMA
> +
> +extern int of_dma_controller_register(struct device_node *np,
> +			int (*of_dma_xlate)(struct of_phandle_args *, void *));
> +extern void of_dma_controller_free(struct device_node *np);
> +extern int of_get_dma_request(struct device_node *np, int index,
> +			      void *out_data);
> +extern unsigned int of_dma_count(struct device_node *np);
> +extern int of_dma_to_resource(struct device_node *dev, int index,
> +			      struct resource *r);
> +
> +extern int of_dma_xlate_onenumbercell(struct of_phandle_args *dma_spec,
> +				      void *dma_req);
> +#else /* CONFIG_OF_DMA */
> +
> +static int of_dma_controller_register(struct device_node *np,
> +			int (*of_dma_xlate)(struct of_phandle_args *, void *))
> +{
> +	return -ENOSYS;
> +}
> +
> +static void of_dma_controller_free(struct device_node *np) {}
> +
> +extern int of_get_dma_request(struct device_node *np, int index,
> +			      void *out_data)
> +{
> +	return -ENOSYS;
> +}
> +
> +static inline unsigned int of_dma_count(struct device_node *np)
> +{
> +	return 0;
> +}
> +
> +static int of_dma_to_resource(struct device_node *dev, int index,
> +			      struct resource *r);
> +{
> +	return -ENOSYS;
> +}
> +
> +static int of_dma_xlate_onenumbercell(struct of_phandle_args *dma_spec,
> +				      void *dma_req)
> +{
> +	return -ENOSYS;
> +}
> +#endif /* CONFIG_OF_DMA */
> +
> +#endif /* __LINUX_OF_DMA_H */
> -- 
> 1.7.9
> 
> 
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-- 
Grant Likely, B.Sc, P.Eng.
Secret Lab Technologies,Ltd.