linux-kernel - Re: [PATCH] regmap: support regmap_field

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Message-ID: <Ytar85UrdSeJuj2Y@sirena.org.uk>
Date:   Tue, 19 Jul 2022 14:04:51 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH] regmap: support regmap_field_write() on non-readable
 fields

On Tue, Jul 19, 2022 at 12:54:02PM +0000, Charles Keepax wrote:
> On Tue, Jul 19, 2022 at 02:14:46PM +0200, Krzysztof Kozlowski wrote:

> > +	if (regmap_readable(field->regmap, field->reg))
> > +		return regmap_update_bits_base(field->regmap, field->reg,
> > +					       mask, val << field->shift,
> > +					       change, async, force);

> I think this will break other valid use-cases, regmap_readable (I
> believe) returns if the register is physically readable, however
> it should still be possible to use update bits if the register is
> in the cache even if it can't physically be read. So really you
> need to fall into this path if it is readable or in the cache.

This is true, we don't currently have a readable_or_cached() check -
this is implemented as trying the cache and only considering actually
reading if there's a read, effectively what we want to do here is force
a cache only read.

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