[alsa-devel] [PATCH] ALSA: usb-audio: set the interface format after resume on Dell WD19

[Kai Heng Feng]

Hi Hui and Takashi,

> On Dec 19, 2019, at 3:06 AM, Takashi Iwai <tiwai at suse.de> wrote:
> 
> On Wed, 18 Dec 2019 14:26:50 +0100,
> Hui Wang wrote:
>> 
>> Recently we found the headset-mic on the Dell Dock WD19 doesn't work
>> anymore after s3 (s2i or deep), this problem could be workarounded by
>> closeing (pcm_close) the app and then reopening (pcm_open) the app, so
>> this bug is not easy to be detected by users.
>> 
>> When problem happens, retire_capture_urb() could still be called
>> periodically, but the size of captured data is always 0, it could be
>> a firmware bug on the dock. Anyway I found after resuming, the
>> snd_usb_pcm_prepare() will be called, and if we forcibly run
>> set_format() to set the interface and its endpoint, the capture
>> size will be normal again. This problem and workaound also apply to
>> playback.
>> 
>> To fix it in the kernel, add a quirk to let set_format() run
>> forcibly once after resume.
>> 
>> Signed-off-by: Hui Wang <hui.wang at canonical.com>
> 
> Thanks, the workaround looks reasonable.
> I applied it now with Cc to stable.

I am not entirely sure it’s a kernel bug. [1] [2] can also fix the issue.

Since USB audio doesn’t have SNDRV_PCM_INFO_RESUME capability,
userspace shouldn’t try to use snd_pcm_resume(). Commit [1] uses 
snd_pcm_drop() to make the device leave suspended state and the device
behaves correctly with the fix.

[1] https://gitlab.freedesktop.org/pulseaudio/pulseaudio/commit/f7b3537bbf9a6916ee3fd72a82025519b4c346f5
[2] https://gitlab.freedesktop.org/pulseaudio/pulseaudio/commit/734a00c849815a45697970d593068c301a04ebbb

Kai-Heng

> 
> 
> Takashi
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