linux-kernel - Re: [PATCH] ALSA: hda: Use maple tree register cache

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Date:   Tue, 13 Jun 2023 18:29:19 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: hda: Use maple tree register cache

On Tue, Jun 13, 2023 at 07:05:21PM +0200, Takashi Iwai wrote:
> Mark Brown wrote:

> > > Oh, I'm afraid that we're seeing different things.  The code there is
> > > rather to *set* some initial value for each amp register (but only
> > > once), and it's not about optimization for writing a same value
> > > again.

> > > That is, the function helps to set an initial (mute) value on each amp
> > > when the driver parses the topology and finds an amp.  But if the
> > > driver already has parsed this amp beforehand by other paths, it skips
> > > the initialization, as the other path may have already unmuted the
> > > amp.

> > So it is possible that we might set two distinct values during setup
> > then and we're doing this intentionally?  It's not obvious that this
> > might happen.  A comment wouldn't hurt, and a big part of this is
> > confusing is that in the non-regmap case all we're doing is suppressing
> > duplicate writes, in that path it's just checking for changes in the
> > register value.

> > None of this is what the non-regmap path does, it just suppresses noop
> > writes to the hardware.

> Actually, many of HD-audio codec driver code heavily relies on the
> regmap, more or less mandatory.  The snd_hda_codec_amp_init() is one
> of such.  You may write a codec driver without the regmap, but some
> helpers won't work as expected.

Sounds like it might be so thinly used it's becoming mandatory to have a
regmap in order to avoid gotchas like there might be with things getting
muted?

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