linux-kernel - Re: linux-6.4 alsa sound broken

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Message-ID: <87wn1pmm4d.wl-tiwai@suse.de>
Date:   Wed, 03 May 2023 18:10:42 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Oswald Buddenhagen <oswald.buddenhagen@....de>
Cc:     Jeff Chua <jeff.chua.linux@...il.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Takashi Iwai <tiwai@...e.de>
Subject: Re: linux-6.4 alsa sound broken

On Mon, 01 May 2023 09:17:20 +0200,
Oswald Buddenhagen wrote:
> 
> On Mon, May 01, 2023 at 11:59:12AM +0800, Jeff Chua wrote:
> > Latest git pull from Linus's tree ... playing a simple sound file will
> > resulted in a lot of echo.
> > 
> how _exactly_ does it sound?
> have you recorded a file through loopback for us to investigate? best
> would be a short sample of a clean wave (sine or sawtooth) with some
> leading and trailing silence.
> 
> > Running on Lenovo X1 with ..
> > 00:1f.3 Audio device: Intel Corporation Alder Lake PCH-P High
> > Definition Audio Controller (rev 01)
> > 
> > I've bisected and reverted the following patch fixed the problem.
> > 
> this seems weird. so my first thought is: are you _sure_ that your
> bisect isn't "contaminated" somehow? is the effect consistent across
> several reboots with the same build? does re-applying my patch
> immediately re-introduce the problem?
> 
> - this code is about silencing. getting dropouts or no playback at all
> would be plausible, while echo (that is, repetition) seems surprising.
>   theoretically, the driver may be setting a bad fill_silence()
> callback   which copies some garbage instead of zeroing, but the HDA
> driver   doesn't set one at all (i.e., uses the default one).
> - this code must be explicitly enabled, which for all i know is done
> by   almost nothing. what players did you try? did you get consistent
> results? did you try taking out audio servers from the equation?
> - the affected hardware belongs to the extremely widely used HDA
> family,   which at the layer the patch is even remotely connected with
> is   completely standardized. so _a lot_ of people should be affected,
> and   we should be getting reports like yours by the dozen. are we?
> 
> of course i can't exclude the possibility that my patch is affected by
> an uninitialized variable or memory corruption (or in the worst case
> causes it), which would of course have very hard to predict
> effects. but that should be investigated properly instead of just
> reverting, lest we might be papering over a much more serious problem.

Oswald, this looks like a real regression by the patch.
Specially, this happens with dmix, and the issue doesn't seem specific
to the driver.  It happens also with USB-audio, not only with
HD-audio.  Just aplay /usr/share/sounds/alsa/Side_Left.wav or whatever
there with the dmix config showed the problem.

The dmix uses the silence_size=boundary as a fill-all operation, and
it's a free-wheel mode, so supposedly something was overlooked in your
code refactoring.

Could you check it and address quickly?  I'd like to fix it before
6.4-rc1 release, so if no fix comes up in a couple of days, I'll have
to revert the change for 6.4-rc1.


thanks,

Takashi