linux-kernel - Re: Question: regmap_field_write()

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Message-ID: <YtAxK1lIooDmdVBP@sirena.org.uk>
Date:   Thu, 14 Jul 2022 16:07:23 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Question: regmap_field_write() - why using update?

On Thu, Jul 14, 2022 at 05:01:29PM +0200, Krzysztof Kozlowski wrote:

> I am converting my driver using MMIO to regmap from readl/writel and to
> my surprise I found that regmap_field_write() does not behave the same
> as regmap_write(). I would expect that they are the same, except one
> operates on fields.

> However regmap_field_write() uses an update method [1] which means it
> reads and performs update. regmap_write() simply writes without a read.

> I find it inconsistent and a bit confusing. Any reasons for such
> behavior so I won't send a patch which breaks 100 of devices?

How would you propose to write to a field without reading the rest of
the bits in the register?  Otherwise you'd be doing a full register
write rather than just a write to the specific field.

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