linux-kernel - Re: [PATCH v2 2/2] dmaengine: dw: fix cyclic transfer callbacks

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Date:	Mon, 11 Jan 2016 15:09:39 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Viresh Kumar <vireshk@...nel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] dmaengine: dw: fix cyclic transfer callbacks

Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:

> On Mon, 2016-01-11 at 13:04 +0000, Mans Rullgard wrote:
>> Cyclic transfer callbacks rely on block completion interrupts which
>> were
>> disabled in commit ff7b05f29fd4 ("dmaengine/dw_dmac: Don't handle
>> block
>> interrupts").  This re-enables block interrupts so the cyclic
>> callbacks
>> can work.  Other transfer types are not affected as they set the
>> INT_EN
>> bit only on the last block.
>> 
>> Fixes: ff7b05f29fd4 ("dmaengine/dw_dmac: Don't handle block
>> interrupts")
>> Signed-off-by: Mans Rullgard <mans@...sr.com>
>
> How did you test that?

With the ABDAC sound driver on the AVR32.  It fails rather miserably
without these patches.

> From my understanding the custom stuff that does cyclic interrupts
> prepares a set of descriptors per period, which at the end of transfer
> will generate XFER interrupt. Next period will go in the same way.
>
> Maybe I missed something.

The cyclic DMA is done by setting up a set of descriptors, one per
period, with the last linked back to the first.  The chain never ends,
so there is never an XFER interrupt.

-- 
Måns Rullgård