linux-kernel - Re: [PATCH 1/2 v2] dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller

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Message-ID: <e9c3a7c20907011758s3188881bqd4beae7192c28162@mail.gmail.com>
Date:	Wed, 1 Jul 2009 17:58:10 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
Cc:	maciej.sosnowski@...el.com, avictor.za@...il.com,
	linux-arm-kernel@...ts.arm.linux.org.uk, patrice.vilchez@...el.com,
	linux-kernel@...r.kernel.org, Atsushi Nemoto <anemo@....ocn.ne.jp>
Subject: Re: [PATCH 1/2 v2] dmaengine: at_hdmac: new driver for the Atmel AHB 
	DMA Controller

On Wed, Jul 1, 2009 at 6:58 AM, Nicolas Ferre<nicolas.ferre@...el.com> wrote:
> Hi,
>
> Just one question Dan (see below).
>
> Nicolas Ferre :
>> This AHB DMA Controller (aka HDMA or DMAC on AT91 systems) is availlable on
>> at91sam9rl chip. It will be used on other products in the future.
>
> [..]
>> +     /*
>> +      * The API requires that no submissions are done from a
>> +      * callback, so we don't need to drop the lock here
>> +      */
>> +     if (callback)
>> +             callback(param);
>
> Even if our dma controller does not seems to take advantage of
> dependency requests...
>
> ...should I add the
> dma_run_dependencies(txd);
> call here to improve conformance to dmaengine standards ?

That would be nice but it is not a strict requirement.

To me it just seems like leaving something for some future developer
to trip over when debugging why channel switching does not work with
this driver.  If you can guarantee that this driver will always be the
only dma_device driver in the system and that future products will not
add additional operation types then maybe it can be omitted.
Otherwise, the overhead of including the call should be negligible.

Regards,
Dan
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