linux-kernel - Re: [PATCH v3 01/17] ALSA: hda: hda_cs_dsp_ctl: Add Library to support CS

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Date:   Fri, 20 May 2022 09:55:13 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Vitaly Rodionov <vitalyr@...nsource.cirrus.com>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Mark Brown <broonie@...nel.org>, <alsa-devel@...a-project.org>,
        <patches@...nsource.cirrus.com>, <linux-kernel@...r.kernel.org>,
        Stefan Binding <sbinding@...nsource.cirrus.com>
Subject: Re: [PATCH v3 01/17] ALSA: hda: hda_cs_dsp_ctl: Add Library to support CS_DSP ALSA controls

On Fri, 20 May 2022 09:50:22 +0200,
Takashi Iwai wrote:
> 
> On Thu, 19 May 2022 19:47:33 +0200,
> Vitaly Rodionov wrote:
> On Thu, 19 May 2022 19:47:33 +0200,
> Vitaly Rodionov wrote:
> > 
> > From: Stefan Binding <sbinding@...nsource.cirrus.com>
> > 
> > The cs35l41 part contains a DSP which is able to run firmware.
> > The cs_dsp library can be used to control the DSP.
> > These controls can be exposed to userspace using ALSA controls.
> > This library adds apis to be able to interface between
> > cs_dsp and hda drivers and expose the relevant controls as
> > ALSA controls.
> > 
> > The apis to add and remove the controls start new threads when
> > adding/removing controls since it is possible that setting an ALSA
> > control would end up calling this api, which would then deadlock.
> 
> Well, I still don't understand why the addition/deletion itself has to
> be in a work.  As far as I see, it's simple calls of snd_ctl_add() and
> snd_ctl_remove_id().
> 
> And, if the problem is that you're calling snd_ctl_add() from another
> control callback, it's rather the problem of the caller's side, not
> here.  IOW, the async implementation should be rather in the caller 
> side.

Also, the description about the newly added controls is missing.
It looks like a really special (non-standard) control that uses TLV
for other purposes, and this must be mentioned somewhere.

And, I wonder what happens with alsactl store/restore with those
controls.  Are TLV contents properly parsed there?


thanks,

Takashi