Re: [PATCH] ALSA: usb-audio: Ignore clock selector errors for single connection

[Alexander Tsoy <alexander@xxxxxxx>]

В Чт, 01/02/2024 в 13:51 +0100, Takashi Iwai пишет:
> On Thu, 01 Feb 2024 12:53:08 +0100,
> Alexander Tsoy wrote:
> > 
> > For devices with multiple clock sources connected to a selector, we
> > need
> > to check what a clock selector control request has returned. This
> > is
> > needed to ensure that a requested clock source is indeed selected
> > and for
> > autoclock feature to work.
> > 
> > For devices with single clock source connected, if we get an error
> > there
> > is nothing else we can do about it. We can't skip clock selector
> > setup as
> > it is required by some devices. So lets just ignore error in this
> > case.
> > 
> > This should fix various buggy Mackie devices:
> > 
> > [  649.109785] usb 1-1.3: parse_audio_format_rates_v2v3(): unable
> > to find clock source (clock -32)
> > [  649.111946] usb 1-1.3: parse_audio_format_rates_v2v3(): unable
> > to find clock source (clock -32)
> > [  649.113822] usb 1-1.3: parse_audio_format_rates_v2v3(): unable
> > to find clock source (clock -32)
> > 
> > There is also interesting info from the Windows documentation [1]
> > (this
> > is probably why manufacturers dont't even test this feature):
> > 
> > "The USB Audio 2.0 driver doesn't support clock selection. The
> > driver
> > uses the Clock Source Entity, which is selected by default and
> > never
> > issues a Clock Selector Control SET CUR request."
> > 
> > Link:
> > https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/usb-2-0-audio-drivers
> >  [1]
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217314
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=218175
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=218342
> > Signed-off-by: Alexander Tsoy <alexander@xxxxxxx>
> > ---
> >  sound/usb/clock.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/sound/usb/clock.c b/sound/usb/clock.c
> > index a8204c6d6fac..60fcb872a80b 100644
> > --- a/sound/usb/clock.c
> > +++ b/sound/usb/clock.c
> > @@ -347,8 +347,16 @@ static int __uac_clock_find_source(struct
> > snd_usb_audio *chip,
> >  			    !writeable)
> >  				return ret;
> >  			err = uac_clock_selector_set_val(chip,
> > entity_id, cur);
> > -			if (err < 0)
> > +			if (err < 0) {
> > +				if (pins == 1) {
> > +					usb_audio_dbg(chip,
> > +						      "%s():
> > selector returned an error, "
> > +						      "assuming a
> > firmware bug, id %d, ret %d\n",
> > +						      __func__,
> > clock_id, err);
> > +					return ret;
> > +				}
> >  				return err;
> > +			}
> 
> Hmm, what's the difference of the behavior except for the additional
> debug message?  Both returns ret, so I don't see how it fixes.

If pins == 1, then ret is returned, otherwise err is returned. They are
not equal here. But yes, the code is a bit confusing.