linux-kernel - Re: [PATCH] dmaengine: add dma_ctrl_cmd to pass buffer stride configuration

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Date:	Tue, 12 Jul 2011 11:58:04 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Sundaram Raju <sundaram@...com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	davinci-linux-open-source@...ux.davincidsp.com,
	linux@....linux.org.uk, linux-omap@...r.kernel.org
Subject: Re: [PATCH] dmaengine: add dma_ctrl_cmd to pass buffer stride configuration

On Mon, Jul 11, 2011 at 11:39 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Mon, Jul 11, 2011 at 2:28 AM, Linus Walleij <linus.walleij@...aro.org> wrote:

> ...and I suspect the slave device drivers that use TI DMA are not
> expected to ever work with other dmaengines?  Likely the case, but
> just wondering out loud.

Typically the OMAP/TI drivers are one-to-one with this specific DMA
controller, but they *can* support controllers without stride options, and
notice that striding will only be used for the display driver IIRC,
pseudo-code:

ret = dmaengine_device_control(chan, TI_DMA_STRIDE_CONFIG,
                        (unsigned long) &my_stride_config);
if (ret) {
   /*
    * OK no striding on this DMA engine, fall back to something else,
    * such as creating an SGlist which emulates the striding with one
    * sglist element per stride.
    */
}

By injecting an error in the stride config path this can even be
properly tested. So it will become an optional acceleration.

Thanks,
Linus Walleij
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