linux-kernel - Re: [PATCH] regmap: spi: Don't use spi_write_then

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Message-ID: <b32120b4-3805-43f0-956d-3c28810fc8b9@sirena.org.uk>
Date: Thu, 20 Mar 2025 23:08:47 +0000
From: Mark Brown <broonie@...nel.org>
To: Arnd Bergmann <arnd@...db.de>, Petr Tesarik <ptesarik@...e.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regmap: spi: Don't use spi_write_then_read()

On Thu, Mar 20, 2025 at 11:00:34PM +0000, Mark Brown wrote:
> Currently SPI reads are implemented using spi_write_then_read(). This is a
> convenience API which as well as constructing a SPI message from parameters
> basically the same as for a bytestream read operation also bounces things
> into a memory buffer to allow callers to use stack or other non-DMAable
> memory. Since regmap should already be ensuring that everything can be
> DMAed further up the stack this copy is redundant so switch to using the
> underlying spi_sync() API with the buffers provided by the core directly.

I think this actually needs to be part of a wider series, but pushing it
out there just now since there's the other regmap paths which also use
spi_sync() and will need any adjustments anyway.

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