linux-kernel - Re: [PATCH 1/3] dma: imx-sdma: Add ssi dual fifo script support

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Message-ID: <20131029135142.GT30088@pengutronix.de>
Date:	Tue, 29 Oct 2013 14:51:43 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Nicolin Chen <b42378@...escale.com>
Cc:	timur@...i.org, shawn.guo@...aro.org, broonie@...nel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	dmaengine@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	alsa-devel@...a-project.org, rob.herring@...xeda.com,
	mark.rutland@....com, swarren@...dotorg.org, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, b32955@...escale.com
Subject: Re: [PATCH 1/3] dma: imx-sdma: Add ssi dual fifo script support

On Tue, Oct 29, 2013 at 08:33:15PM +0800, Nicolin Chen wrote:
> There's a script for SSI missing in current sdma script list. Thus add it.
> This script would allow SSI use its dual fifo mode to transimit/receive
> data without occasional hardware underrun/overrun.
> 
> This patch also fixed a counting error for total number of scripts.

Look at drivers/dma/imx-sdma.c:

> /**
>  * struct sdma_firmware_header - Layout of the firmware image
>  *
>  * @magic		"SDMA"
>  * @version_major	increased whenever layout of struct
>  * sdma_script_start_addrs
>  *			changes.

Can you image why this firmware has a version field? Right, it's because
it encodes the layout of struct sdma_script_start_addrs.

As the comment clearly states you have to *increase this field* when you
add scripts.

Obviously you missed that, as the firmware on lkml posted recently
shows:

> 00000000: 414d4453 00000001 00000001 0000001c SDMA............
                     ^^^^^^^^
                     Still '1'

> 00000010: 00000026 000000b4 0000067a 00000282 &.......z.......
> 00000020: ffffffff 00000000 ffffffff ffffffff ................
> 00000030: ffffffff ffffffff ffffffff ffffffff ................
> 00000040: ffffffff ffffffff 00001a6a ffffffff ........j.......
> 00000050: 000002eb 000018bb ffffffff 00000408 ................
> 00000060: ffffffff 000003c0 ffffffff ffffffff ................
> 00000070: ffffffff 000002ab ffffffff 0000037b ............{...
> 00000080: ffffffff ffffffff 0000044c 0000046e ........L...n...
> 00000090: ffffffff 00001800 ffffffff ffffffff ................
> 000000a0: 00000000 00001800 00001862 00001a16 ........b.......
                              ^^^^^^^^^^^^^^^^^
                              new script addresses introduced


> -#define SDMA_SCRIPT_ADDRS_ARRAY_SIZE_V1	34
> +#define SDMA_SCRIPT_ADDRS_ARRAY_SIZE_V1	37

And no, this is not a bug. It's your firmware header that is buggy.

What you need is:

#define SDMA_SCRIPT_ADDRS_ARRAY_SIZE_V2      37

You (you as a company, not you as a person) knew that it was me who
created this firmware format. So it was absolutely unnecessary to create
an incompatible firmware instead of dropping me a short note.

Please add a version check to the driver as necessary and provide a proper
firmware.

Sascha

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