Subject: [RFC PATCH 1/2] of: Add generic device tree DMA helpers

From: [email-masked] (Nicolas Ferre)
Date: Wed, 22 Feb 2012 11:59:14 +0100

On 01/27/2012 06:29 PM, Cousson, Benoit :
> Add some basic helpers to retrieve a DMA controller device_node
> and the DMA request line number.
> 
> For legacy reason another API will export the DMA request number
> into a Linux resource of type IORESOURCE_DMA.
> This API is usable only on system with an unique DMA controller.

Hi,

I followed that discussion and I like very much the biding that Benoit
is proposing. It will help me a lot with my current work on Atmel DMA
controller.

If I understand correctly, some rework is needed before it can be
integrated in a stable git tree (I mean before we can base our work on
top of it). So, in the meantime, what should I do to help and make
things go forward? to be quite frank, I would be interested to have a
working DMA enabled device soon ;-)
Do you think that 3.4 is out of reach?

Best regards,

> Signed-off-by: Benoit Cousson <[email-masked]>
> Cc: Grant Likely <[email-masked]>
> Cc: Rob Herring <[email-masked]>
> ---
>  Documentation/devicetree/bindings/dma/dma.txt |   44 +++++++++
>  drivers/of/Kconfig                            |    5 +
>  drivers/of/Makefile                           |    1 +
>  drivers/of/dma.c                              |  130 +++++++++++++++++++++++++
>  include/linux/of_dma.h                        |   49 +++++++++
>  5 files changed, 229 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..7f2a301
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/dma.txt
> @@ -0,0 +1,44 @@
> +* 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 properties:
> +    - dma-controller: Mark the device as a DMA controller
> +    - #dma-cells: Number of cell for each DMA line, must be one.
> +
> +
> +Example:
> +
> +	sdma: dma-controller at 48000000 {
> +		compatible = "ti,sdma-omap4"
> +		reg = <0x48000000 0x1000>;
> +		interrupts = <12>;
> +        dma-controller;
> +		#dma-cells = <1>;
> +	};
> +
> +
> +
> +* DMA client
> +
> +Client drivers should specify the DMA request numbers using a phandle to
> +the controller + the DMA request number on that controller.
> +
> +Required properties:
> +    - dma-request: List of pair phandle + dma-request per line
> +    - 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
> +
>  endmenu # OF
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index a73f5a5..d08443b 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..d4927e2
> --- /dev/null
> +++ b/drivers/of/dma.c
> @@ -0,0 +1,130 @@
> +/*
> + * 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/of.h>
> +#include <linux/of_dma.h>
> +
> +/**
> + * of_get_dma_request() - Get a DMA request number and dma-controller node
> + * @np:		device node to get DMA request from
> + * @propname:	property name containing DMA specifier(s)
> + * @index:	index of the DMA request
> + * @ctrl_np:	a device_node pointer to fill in
> + *
> + * Returns DMA number along to the dma controller node, or one of the errno
> + * value on the error condition. If @ctrl_np is not NULL the function also
> + * fills in the DMA controller device_node pointer.
> + */
> +int of_get_dma_request(struct device_node *np, int index,
> +		       struct device_node **ctrl_np)
> +{
> +	int ret = -EINVAL;
> +	struct of_phandle_args dma_spec;
> +
> +	ret = of_parse_phandle_with_args(np, "dma-request", "#dma-cells",
> +					 index, &dma_spec);
> +	if (ret) {
> +		pr_debug("%s: can't parse dma property\n", __func__);
> +		goto err0;
> +	}
> +
> +	if (dma_spec.args_count > 0)
> +		ret = dma_spec.args[0];
> +
> +	if (ctrl_np)
> +		*ctrl_np = dma_spec.np;
> +	else
> +		of_node_put(dma_spec.np);
> +
> +err0:
> +	pr_debug("%s exited with status %d\n", __func__, ret);
> +	return ret;
> +}
> +EXPORT_SYMBOL(of_get_dma_request);
> +
> +/**
> + * 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(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;
> +
> +	if (!r)
> +		return -EINVAL;
> +
> +	dma = of_get_dma_request(dev, index, NULL);
> +	if (dma < 0)
> +		return dma;
> +
> +	/*
> +	 * 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;
> +
> +	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..575163d
> --- /dev/null
> +++ b/include/linux/of_dma.h
> @@ -0,0 +1,49 @@
> +/*
> + * 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_GPIO
> +
> +extern int of_get_dma_request(struct device_node *np, int index,
> +		       struct device_node **ctrl_np);
> +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);
> +
> +#else /* CONFIG_OF_DMA */
> +
> +static int of_get_dma_request(struct device_node *np, int index,
> +			      struct device_node **ctrl_np);
> +{
> +	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;
> +}
> +
> +#endif /* CONFIG_OF_DMA */
> +
> +#endif /* __LINUX_OF_DMA_H */

-- 
Nicolas Ferre