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

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Message-ID: <e48bbd3b-544d-43d5-82a1-8fbbcb8cd1a4@sirena.org.uk>
Date:   Tue, 13 Jun 2023 14:59:14 +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 09:36:34AM +0200, Takashi Iwai wrote:

> This is an error from regache_sync_val(), and it indicates that the
> synced register is write-only; regcache_maple_sync() tries to sync all
> cached values no matter whether it's writable or not, then hitting
> this.

BTW I was just looking at reg_raw_update_once() and I can't figure out
why it's trying to do what it's doing - it does a read to check if it's
seen the register before and then does an _update_bits() if the register
hasn't been cached yet, apparently trying suppress duplicate writes but
possibly deliberately discarding changes to multiple bitfields in the
same register.  That's not what the non-regmap path does, it'll only
discard noop changes to the same bitfield.

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