linux-kernel - Re: [PATCH] ALSA: usb-audio: fix incorrect clock source setting

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Date:   Sun, 25 Jul 2021 09:44:01 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Geraldo Nascimento <geraldogabriel@...il.com>
Cc:     chihhao.chen@...iatek.com, alsa-devel@...a-project.org,
        wsd_upstream@...iatek.com, damien@...audio.com, tiwai@...e.com,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        matthias.bgg@...il.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ALSA: usb-audio: fix incorrect clock source setting

On Sat, 24 Jul 2021 17:04:13 +0200,
Geraldo Nascimento wrote:
> 
> On Sat, Jul 24, 2021 at 8:05 AM Takashi Iwai <tiwai@...e.de> wrote:
> >
> > This looks like a regression introduced by the recent commit
> > d2e8f641257d ("ALSA: usb-audio: Explicitly set up the clock
> > selector"), which is a fix for certain devices.  Too bad that the
> > behavior really depends on the device...
> 
> Dr. Iwai, perhaps we could restrict the generalized fix for the
> Behringer UFX1604 / UFX1204 with some simple logic to devices that
> only have *one* clock source.
> 
> In that case the clock selector must be set to the only clock source.
> 
> This way we keep the generalization without breaking devices with more
> than one clock source.
> 
> Just an idea.

I don't think it's easy to generalize.  All those bugs are more or
less BIOS bugs, and a logic doesn't apply always, just because it's a
bug :)  For example, setting the clock selector itself should be a
valid operation from the specification POV, while this leads to
breakage on some devices.  So, even if we add a more generic
workaround, we need to see which side effect is more commonly seen at
first.


Takashi