linux-kernel - Re: [PATCH] dmaengine: imx-sdma: Add DMA event remapping for imx6sx-sdma

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Date:	Mon, 20 Apr 2015 11:45:41 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Nicolin Chen <nicoleotsuka@...il.com>
Cc:	vinod.koul@...el.com, fabio.estevam@...escale.com,
	b38343@...escale.com, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, dan.j.williams@...el.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org
Subject: Re: [PATCH] dmaengine: imx-sdma: Add DMA event remapping for
 imx6sx-sdma

On Tue, Apr 14, 2015 at 10:39:11PM -0700, Nicolin Chen wrote:
> The SDMA on imx6sx has a few DMA event remapping configurations
> inside the GPR (General Purpose Register) of that SoC. When users
> want to use a non-default DMA event, they need to configure the
> GPR register. So this patch gives an interface of the GPR and
> implements it in the SDMA driver so as to finish the DMA event
> remapping.
> 
> Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
> ---
>  .../devicetree/bindings/dma/fsl-imx-sdma.txt       |  9 ++++
>  drivers/dma/imx-sdma.c                             | 58 ++++++++++++++++++++++
>  2 files changed, 67 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt b/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> index dc8d3aa..03315a6 100644
> --- a/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> +++ b/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> @@ -8,6 +8,7 @@ Required properties:
>        "fsl,imx51-sdma"
>        "fsl,imx53-sdma"
>        "fsl,imx6q-sdma"
> +      "fsl,imx6sx-sdma"
>    The -to variants should be preferred since they allow to determine the
>    correct ROM script addresses needed for the driver to work without additional
>    firmware.
> @@ -19,6 +20,14 @@ Required properties:
>  - fsl,sdma-ram-script-name : Should contain the full path of SDMA RAM
>    scripts firmware
>  
> +Optional properties:
> +- fsl, sdma-event-remap : List of one or more DMA event remapping
> +  configurations. Its format: <&gpr addr shift val>
> +	gpr : the gpr phandle
> +	addr : the register address of the GPR
> +	shift : the bit shift of the GPR register
> +	val : the value of that bit

This binding allows arbitrary register writes to the GPR register space.
I don't think we want to allow that. A binding for this if necessary at
all must be higher level.

> +static int sdma_event_remap(struct sdma_engine *sdma)
> +{
> +	struct device_node *np = sdma->dev->of_node;
> +	char propname[] = "fsl,sdma-event-remap";
> +	struct of_phandle_args gpr_spec;
> +	struct regmap *gpr;
> +	int i = 0, ret = 0;
> +
> +	/* Only support DT */
> +	if (IS_ERR(np))
> +		return ret;
> +
> +	/* Only apply to imx6sx platform */
> +	if (!of_device_is_compatible(np, "fsl,imx6sx-sdma"))
> +		return ret;

We already have struct sdma_driver_data. Please add a have_remap field
or similar there.

> +
> +	/* Bypass if no need to remap */
> +	if (!of_find_property(np, propname, NULL))
> +		return ret;
> +
> +	/* Fetch the remap configurations of GPR */
> +	ret = of_parse_phandle_with_args(np, propname, "#gpr-cells", i++,
> +					 &gpr_spec);
> +	if (ret) {
> +		dev_err(sdma->dev, "failed to get a correct %s property: %d\n",
> +				propname, ret);
> +		return ret;
> +	}
> +
> +next:
> +	gpr = syscon_node_to_regmap(gpr_spec.np);
> +	if (IS_ERR(gpr)) {
> +		ret = PTR_ERR(gpr);
> +		dev_err(sdma->dev, "failed to get gpr regmap: %d\n", reg);
> +		return ret;
> +	}
> +
> +	/* 0 : Register address, 1 : Bit shift, 2 : Bit value */
> +	regmap_update_bits(gpr, gpr_spec.args[0], BIT(gpr_spec.args[1]),
> +			   gpr_spec.args[2] << gpr_spec.args[1]);
> +
> +	if (!of_parse_phandle_with_args(np, propname, "#gpr-cells", i++,
> +					&gpr_spec))
> +		goto next;

C has native support for loops. Please use it.

Sascha

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