linux-kernel - Re: [RFC PATCH] regmap: force update_bits() to write to HW when reg is volatile

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Message-ID: <643e5dd9-2d1f-4cc7-90e0-22e4a07ecd0f@sirena.org.uk>
Date:   Fri, 28 Apr 2023 14:21:38 +0100
From:   Mark Brown <broonie@...nel.org>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
Cc:     Matti Vaittinen <mazziesaccount@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] regmap: force update_bits() to write to HW when reg
 is volatile

On Fri, Apr 28, 2023 at 12:36:51PM +0000, Vaittinen, Matti wrote:
> On 4/28/23 14:35, Mark Brown wrote:

> > I think you're looking for regmap_write_bits() here.

> Yes. Thanks for pointing this out to me. This is the functionality I 
> searched for.

> However, my question really was if the regmap_update_bits() (and 
> regmap_set_bits() / regmap_clear_bits()) should automatically work as 
> regmap_write_bits() for volatile registers. I'll take your answer as 
> "no" - and try to remember just use regmap_write_bits() with volatile 
> registers which may require forcing writing the value even when it is 
> not changed. Thanks!

Yeah, like you said in your commit there are cases where suppressing the
write is still useful - you might have some bits that are volatile and
some not or you might have something like a pattern where the hardware
can set bits and the host writes 1 to clear.  One common thing is to
have read only status bits mixed in with normal read/write bits.

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