linux-kernel - Re: [PATCH] pinctrl: cy8c95x0: Cache muxed registers

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Message-ID: <CACRpkdZhY_Yz2jHGXWO5_t8Qdey8me0Gytds7V64GYOFoEC2Dg@mail.gmail.com>
Date: Tue, 14 May 2024 10:51:17 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Patrick Rudolph <patrick.rudolph@...ements.com>, Mark Brown <broonie@...nel.org>
Cc: Andy Shevchenko <andy.shevchenko@...il.com>, naresh.solanki@...ements.com, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pinctrl: cy8c95x0: Cache muxed registers

On Tue, May 14, 2024 at 10:39 AM Patrick Rudolph
<patrick.rudolph@...ements.com> wrote:

> Do you have an example where muxed registers are used in a regmap?
> Is there some documentation available explaining the existing
> mechanism? I'm not aware of anything.

The regmap is sadly undocumented I have had it on my list for a long
time to document this gem, but I never find the time.

You have to mark registers that cannot be cached as volatile, then
enable caching in the regmap with e.g. .cache_type = REGCACHE_FLAT
in the regmap config, then it pretty much caches itself.
<linux/regmap.h> has some cache maintenance functions if you
run into corner cases.

(Mark will correct me if I say something wrong...)

Yours,
Linus Walleij