linux-kernel - Re: [PATCH] regmap: prevent noinc writes from clobbering cache

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Message-ID: <ZUKy-ETSbM7yNvNK@dell-precision-5540>
Date:   Wed, 1 Nov 2023 16:20:08 -0400
From:   Ben Wolsieffer <ben.wolsieffer@...ring.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ben Whitten <ben.whitten@...il.com>
Subject: Re: [PATCH] regmap: prevent noinc writes from clobbering cache

Hi Mark,

On Wed, Nov 01, 2023 at 05:05:39PM +0000, Mark Brown wrote:
> On Wed, Nov 01, 2023 at 10:29:27AM -0400, Ben Wolsieffer wrote:
> > Currently, noinc writes are cached as if they were standard incrementing
> > writes, overwriting unrelated register values in the cache. Instead, we
> > want to cache the last value written to the register, as is done in the
> > accelerated noinc handler (regmap_noinc_readwrite).
> 
> Could you please add a kunit test for this?

I started to look into this, but it is not currently possible to test
noinc behavior with regmap_[raw_]ram. The same bulk write operation is
used by both incrementing and non-incrementing writes, and the difference
in behavior is due to how the hardware handles the bulk write to a
particular register.

To test this behavior, regmap_raw_ram (raw because it supports bulk
writes) would have to be told that certain of its registers should
implement noinc semantics.

Is this something I should implement?

Thanks, Ben