[alsa-devel] [PATCH 0/1] ALSA: hda: add fallback to polling to hdac_bus_get_response()

[Takashi Iwai]

On Fri, 04 Oct 2019 16:35:26 +0200,
Kai Vehmanen wrote:
> 
> Hey all,
> 
> while debugging issues with some Intel platforms related to display
> audio codec probe (see
> https://lists.freedesktop.org/archives/intel-gfx/2019-October/214621.html ),
> I found a discrepancy in behaviour between snd-hda-intel and SOF, despite
> using the same snd-hda-codec-hdmi as the codec driver.
> 
> The specific problem I was debugging appears in a stress test
> (designed to uncover the above display driver issue) where
> driver-unload, s3-suspend, resume and driver-reload is done in a loop
> and repeated for hundreds of iterations. When using SOF, I would get
> occasional probe fail due to a missing HDA irq. The AZX snd_hda_intel
> driver nicely survives this test. The explanation seems to be differences
> in the hdac get_response() implementation.
> 
> While the specific issue could be solved with other means,
> the git history shows a number of rare issues with HDA codecs
> where polling has helped. It would seem best to align the logic
> with the AZX driver implementation that has seen much more usage
> over the years. This will benefit SOF and any other users of the HDAC
> library.

While it's OK to add the polling support in the core code, I suspect
that the main problem gets solved by setting the write_sync flag as
the commit 2756d9143aa5.  For SOF/SST, you may set the flag
unconditionally since they support only the new chipsets.

I've been traveling (still for the next week), so the further reply
may be delayed.


thanks,

Takashi