[alsa-devel] Problem and Patch for B&W PX Bluetooth Headphones

[Takashi Iwai]

On Fri, 28 Sep 2018 20:03:25 +0200,
Nicolas Herochao wrote:
> 
> Hello,
> 
> I'm writing this mail because of a Crash when connecting the B&W PX
> headphones via usb. Half a year ago this used to work with Linux after
> setting the default sample rate of pulseaudio to 48000k.
> 
> A Launchpad Bug seems to describe this exact issue (detailed
> description below):
> https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/1773697.
> It pointed me to the right direction, and today I have successfully
> compiled and tested a small patch that fixes the errors while also
> setting the sample rate to 48000k, making these headphones plug&play
> on any newer firmware. They sound awesome via USB!
> 
> I would like to submit this patch, but it would be my first
> contribution and it could potentially break the B&W PX on older
> firmware. I can't test it since I see no obvious ways to downgrade the
> firmware. The automatic detection of these headphones always worked
> except for the sample-rate and perhaps the worst result is that old
> firmware will show a non-functional microphone, like on Windows.
> 
> So I decided to first present the patch on this mailing list and ask
> for feedback and help. If anyone wants to pick the patch up, I'd
> appreciate that as well.
> 
> My questions:
> 
> * Can a quirk somehow handle multiple firmware versions of a usb device?

Currently not for a straightforward quirk table.
Can we identify easily the firmware version on this device?
If it's found in some id field, we can add the check and apply
conditionally.

> * If not: Will this quirk allow old firmware to work out of the box
> but show a non-functional microphone? (And is that okay?)

Yes, a good option as a quick fix for now.


> Thanks for your time and any feedback you can provide!
> Sincerely,
> 
> Nicolas
> 
> PS: more detail on the cause of the issue:
> ------
> 
> A quirk in snd-usb-audio was added to automate setting sample rate to
> 4800k and remove the previously exposed nonfunctional microphone:
> commit 240a8af929c7c57dcde28682725b29cf8474e8e5
> https://lore.kernel.org/patchwork/patch/919689/
> 
> However the headphones where updated shortly after that to remove the
> unintentional microphone functionality. I guess because of this the
> headphones now crash when connecting them via USB while the quirk is
> active with the following dmesg errors:
> 
> snd-usb-audio: probe of 2-3:1.0 failed with error -22
> usb 2-3: 2:1: cannot get min/max values for control 2 (id 2)

Could you put this explanation into the patch description?


> ---------------
> Finally, here is the patch (based on the current mainline kernel and
> generated according to all Guidelines I could find) which fixes the
> quirk by removing the microphone part:

... and this one should be also merged into the patch description.

> ----------------
> 
> From 748587283db85e219902abf4ac012864005943c8 Mon Sep 17 00:00:00 2001
> From: Nicolas Huaman <nicolas at herochao.de>
> Date: Fri, 28 Sep 2018 18:05:15 +0200
> Subject: [PATCH 1/1] SOUND: update quirk for B&W PX to remove microphone

... what I meant is to put the explanations and other nice texts into
*here*.

> Signed-off-by: Nicolas Huaman <nicolas at herochao.de>

Also, last but not least, please align the patch subject line.
The prefix is like "ALSA: usb-audio:", and you can drop "1/1" if there
is only one patch.

The code changes look OK to me, so it'd be great if you can resubmit
with the corrections above.


thanks,

Takashi