[alsa-devel] omap-mcbsp: TX Buffer Overflow

[Tomas Novotny]

Hi,

we have AM3703 based board similar to BeagleBoard. I'm hitting this error
after upgrade to latest LTS 4.19.71 (upgraded from 4.1):

omap-mcbsp 49022000.mcbsp: TX Buffer Overflow!

This appears during or after playing of short (~2s) ding-dong wav. That error
exists for longer time, because handling of tx buffer overflow irq was
introduced in 2016: 4e85e7776eba ("ASoC: omap-mcbsp: Enable TX/RX under and
overflow interrupts"). I've cherry-picked it to 4.1 and I see the error there also.
The sound seems clear and ok to me, but we are using low quality speaker.

There are two workarounds to get rid of the message:
1) Change 'dma_op_mode' sysfs attribute from 'element' to 'threshold'. I
found that just by coincidence when checking sysfs attributes.
2) Compile kernel with CONFIG_VIDEO_OMAP3=y. Found on Logic PD forum [1].

Does anybody have any idea what's going wrong? Or why these (somehow)
unrelated workarounds help?

Thanks,

Tomas

[1] https://support.logicpd.com/TDGForum/tabid/124/aft/2277/Default.aspx