[alsa-devel] Swapped channels issue on pxa-ssp based platforms

[Haojian Zhuang]

On Tue, Nov 8, 2011 at 1:40 AM, Daniel Mack <zonque at gmail.com> wrote:
> Hi,
>
> we're hunting a weird bug on PXA3xx/ssp based audio devices which causes
> the playback channels to be swapped when the capture stream is started
> at the same time. Content for the left channel appears on the right and
> vice versa, in approximately 50% of all test runs of the following command:
>
>   $ arecord -f cd - -D hw:0,0  | aplay -D hw:0,0  -f cd -
>
> When just aplay is used, everything's fine.
>
> It's unrelated to the codec part, as we see this with machines that
> feature different models. I guess this is some sort of a race condition
> in the stream startup, and suspected sound/soc/pxa/pxa-ssp.c to lack
> some locking, so I added a spinlock around all register
> read-modify-write cycles. But that doesn't seem to be the reason.
>
> It could also be the DMA engine that writes to the wrong position, but I
> fail to see it right now.
>
> Does anyone have an idea where to look for the culprit? Have there been
> similar effects in other SoC platforms?
>
> Thanks for sharing your thoughts :)
>
>
> Daniel
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Hi Daniel,

I assumed that you're using pxa3xx or pxa93x silicons. Do you also
enable D0CS operating point? If you disable this operating point, does
this issue exist?

If the codec is configured as master mode, does this issue exist?

Thanks
Haojian