omap-mcbsp 49022000.mcbsp: TX Buffer Overflow!

[Peter Ujfalusi]

Hi,

On 14/07/2020 21.03, Jarkko Nikula wrote:
> Hi
> 
> On 7/11/20 6:33 AM, Dave Young wrote:
>> Hi,
>>
>> I'm trying to use g_audio on my Nokia N900 with mainline kernel. Seems
>> it does not work.  No sound when I play from a laptop, and also see a
>> lot of error like below:
>> [ 4729.557647] omap-mcbsp 49022000.mcbsp: TX Buffer Overflow!
>> ...
>>
> Head 0dc589da873b ("Merge tag 'iommu-fixes-v5.8-rc5' of
> git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu") records and
> plays fine here (arecord -f dat |aplay), although I see some of those
> errors but don't hear any glitches etc.
> 
> Peter, does above indicate a serious issue or is it perhaps a false
> alarm on OMAP3 (no audible glitches)?

I need to dig out my n900 or beagleXM, but it is hard to believe it is
not a result of a glitch.
The DMA is triggered by McBSP and it should write exactly what McBSP
expects to be receiving.

I can not recall any changes in the past years which would have
introduced regressions in McBSP or the sDMA driver.

> I believe you don't have some mixer knob on, N900 audio path is somewhat
> complex and needs bunch of mixer switches and volumes to be set. I
> attached my N900 mixer scripts for you to try.

This could be the reason for the silence, I have asoundrc files
somewhere to restore a 'good' mixer config.

> Set first everything off:
> ./aic34_scripts/shutdown.sh
> 
> Then enable internal digital microphone and speakers:
> ./aic34_scripts/dmic.sh
> ./aic34_scripts/speakers.sh
> 
> Hopefully these help you get going :-)
> 

- Péter

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