linux-kernel - Re: [PATCH 1/1] axi-i2s: set period size register

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Message-ID: <263e42b4-75a3-183c-894b-e485e387eccf@lucaceresoli.net>
Date:   Mon, 27 Aug 2018 18:22:37 +0200
From:   Luca Ceresoli <luca@...aceresoli.net>
To:     Lars-Peter Clausen <lars@...afoo.de>, alsa-devel@...a-project.org
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-kernel@...r.kernel.org,
        Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH 1/1] axi-i2s: set period size register

Hi,

thanks for your feedback.

[Adding Michal Simek (Xilinx maintainer) in Cc]

On 27/08/2018 14:27, Lars-Peter Clausen wrote:
> On 08/24/2018 06:04 PM, Luca Ceresoli wrote:
>> The default value of the PERIOD_LEN register is 0 and results in
>> axi-i2s keeping TLAST always asserted in its AXI Stream output.
>>
>> When the AXI Stream is sent to a Xilinx AXI-DMA, this results in the
>> DMA generating an interrupt flood and ALSA produce a corrupted
>> recording. This is because AXI-DMA raises an interrupt whenever TLAST
>> is active.
>>
>> Fix by setting the PERIOD_LEN register as soon as the period is
>> known. This way TLAST is emitted once per period, and the DMA raises
>> interrupts correctly.
> 
> The patch looks OK. But I'd prefer not to merge it if possible.
> 
> We've done some early experiments with the Xilinx AXI-DMA, but it turned out
> to be to unreliable and we've abandoned support for it. One of the more
> critical issues was that you can't abort a DMA transfer. That means when
> audio capture is stopped the DMA will halt, but not complete the current
> transfer. Then when the next audio capture start the DMA will continue with
> the previous transfer. The observed effect of this was that the system would
> just crash randomly (Presumably due to memory corruption).

Strange. I have done many capture experiments with arecord and didn't
run into such bad issues. I only have a much less serious problem
(garbage or old samples in the first few buffers), but no crashes.

Michal, are you aware of these problems?

> Have you considered using the ADI AXI-DMAC? That should work just fine.

Not until today, because AXI-DMA is working here.

I'd like to better understand what's going on before changing an IP that
is working. Do you have additional details about your setup? How do you
run your tests?

Regards,
-- 
Luca