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

[Tony Lindgren]

* Ladislav Michl <ladis at linux-mips.org> [190907 09:14]:
> 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).

Hmm I wonder if this is still related to the SoC idling?
See commit 9834ffd1ecc3 ("ASoC: omap-mcbsp: Add PM QoS support for McBSP
to prevent glitches"), maybe something still needs to be fixed in that
area.

> 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.

These mean the devices should really have separate nodes
in the dts rather than combining multiple devices into a
single node with multiple reg entries.

The issue with combining multiple devices into a single device
is that flushing posted write with a read back to one register
range will not flush it for the other which can cause mysterious
bugs.

Regards,

Tony