linux-kernel - Re: [PATCH] regmap: Add debugfs file for forcing field writes

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Message-ID: <443d4c43-080e-48b2-80ee-13e2df10c6eb@sirena.org.uk>
Date:   Mon, 12 Jun 2023 16:00:06 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Waqar Hameed <waqar.hameed@...s.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, kernel@...s.com
Subject: Re: [PATCH] regmap: Add debugfs file for forcing field writes

On Mon, Jun 12, 2023 at 04:53:35PM +0200, Waqar Hameed wrote:
> `_regmap_update_bits` checks if the current register value differs from
> the new value, and only writes to the register if they differ. When
> testing hardware drivers, it might be desirable to always force a
> register write, for example when writing to a `regmap_field`.
> 
> This enables and simplifies testing and verification of the hardware
> interaction. For example, when using a hardware mock/simulation model,
> one can then more easily verify that the driver makes the correct
> expected register writes during certain events. Add a bool variable
> `force_write_field` and a corresponding debugfs entry.

If we're going to do something like this which could interfere with
driver operation then it should be guarded like the write support is so
that people using it have to modify the kernel to get the feature, or at
the very least taint the kernel.  This is less invasive but still might
cause issues if someone is relying on read/modify/write behaviour.

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