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

[Ladislav Michl]

On Fri, Sep 06, 2019 at 04:51:09PM +0200, Tomas Novotny wrote:
> 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.

Just FYI, for stream capture there's
omap-mcbsp 49022000.mcbsp: RX Buffer Underflow!

As far as I remember all stable kernels we have in production - 4.9.x, 4.14.x and
4.19.x - are affected. IGEPv2 with both DM3730 and OMAP3530 are affected
(headless machines, CONFIG_VIDEO_OMAP3=n).

And DT is probably worth updating:
omap_hwmod: mcbsp2_sidetone using broken dt data from mcbsp
omap_hwmod: mcbsp3_sidetone using broken dt data from mcbsp

I never motivated myself to dig deeper as catured stream looks pretty normal.

	l.

> 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