Re: [PATCH v4 0/3] ALSA: usb-audio: Add QUIRK_FLAG_MIXER_GET_CUR_BROKEN

[Takashi Iwai <tiwai@suse.de>]

On Sun, 31 May 2026 17:45:19 +0200,
Rong Zhang wrote:
> 
> Since commit 86aa1ea1f15c ("ALSA: usb-audio: Do not expose sticky
> mixers"), the UAC mixer core utilizes volume SET_CUR and GET_CUR to
> identify devices with sticky mixers. Unfortunately, even though most
> devices with sticky GET_CUR also have corresponding sticky SET_CUR,
> which I actually met more since the commit had been merged, there is
> also a rare case that some devices may have volume mixers that responds
> to SET_CUR properly but with its GET_CUR stubbed. This cause the sticky
> check to consider the mixer to be sticky and unnecessarily disable it.
> 
> As the sticky check can't distinguish between sticky mixers and working
> SET_CUR but broken GET_CUR, add QUIRK_FLAG_MIXER_GET_CUR_BROKEN to tell
> that the device should fall into the second category when GET_CUR
> returns a constant value. In this case, the sticky check becomes
> non-fatal and only disables GET_CUR instead of the whole mixer. The
> current volume will then be provided by the internal cache that stores
> the last set volume.
> 
> An info message prompting users to check MIXER_GET_CUR_BROKEN for
> potential sticky mixers is also added, so that users can learn how to do
> some experiments to determine what's going on. If the mixer surprisingly
> turns out to be non-sticky, they can submit a patch for a new quirk
> table entry.
> 
> The Sennheiser MOMENTUM 3 and Edifier MF200 need the quirk flag. Though
> their UAC mixers respond to SET_CUR by tuning the volume, the
> corresponding GET_CUR methods are somehow stubbed and return constant
> values, resulting in them being disabled by the sticky check.
> 
> Signed-off-by: Rong Zhang <i@rong.moe>
> ---
> Changes in v4:
> - Rebase since a patch improving the error path of the sticky check has
>   been applied earlier
>   - https://patch.msgid.link/20260531-uac-sticky-error-path-v1-1-12c2329d17ef@rong.moe
> - Integrate a follow-up series into this one
>   - https://patch.msgid.link/20260531-uac-edifier-mf200-v1-0-be69657c3f87@rong.moe
> - Link to v3: https://patch.msgid.link/20260529-uac-quirk-get-cur-vol-v3-0-bde363188ca4@rong.moe
> 
> Changes in v3:
> - Make the log less noisy (thanks Takashi Iwai)
> - Do not propagate mixer values written by sanity checks when GET_CUR is
>   broken, nor restore the garbage backed-up value. Instead, rely on
>   init_cur_mix_raw() to initialize the mixer properly
> - Gate cache invalidation as well, so that the current volume is always
>   available to userspace
> - Update the comment of check_sticky_volume_control()
> - Link to v2: https://patch.msgid.link/20260528-uac-quirk-get-cur-vol-v2-0-84d3c8f48150@rong.moe
> 
> Changes in v2:
> - Turn the approach into a less radical one
>   - Rename the quirk flag to QUIRK_FLAG_MIXER_GET_CUR_BROKEN
>   - Add a flag `get_cur_broken' to `struct usb_mixer_elem_info'
>   - When the sticky check fails, check quirk flags. Gate further GET_CUR
>     by setting `cval->get_cur_broken' if QUIRK_FLAG_MIXER_GET_CUR_BROKEN
>     is set, otherwise disable the mixer as usual
>   - The quirk flag still applies to all mixers, but as long as a mixer
>     makes the sticky check happy, it won't be affected at all. Only
>     those mixers with constant GET_CUR values will have their GET_CUR
>     gated. I assume the impact is minimal, since it's very unlikely a
>     device would have sticky mixers (broken SET_CUR) along with mixers
>     with working SET_CUR but broken GET_CUR at the same time
> - Link to v1: https://patch.msgid.link/20260527-uac-quirk-get-cur-vol-v1-0-e9362b712e5e@rong.moe
> 
> ---
> Rong Zhang (3):
>       ALSA: usb-audio: Add QUIRK_FLAG_MIXER_GET_CUR_BROKEN
>       ALSA: usb-audio: Add quirk flag for Sennheiser MOMENTUM 3
>       ALSA: usb-audio: Add quirk flag for Edifier MF200

Now took all three patches onto for-next branch.  Thanks.


Takashi