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

From: Måns Rullgård
Date: Mon Jan 11 2016 - 10:09:46 EST

Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> 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
>> bit only on the last block.
>> Fixes: ff7b05f29fd4 ("dmaengine/dw_dmac: Don't handle block
>> interrupts")
>> Signed-off-by: Mans Rullgard <mans@xxxxxxxxx>
> 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