linux-kernel - Re: [PATCH v2 2/2] iio: accel: Add driver support for ADXL355

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Message-ID: <20210723174751.GL5221@sirena.org.uk>
Date:   Fri, 23 Jul 2021 18:47:51 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Puranjay Mohan <puranjay12@...il.com>,
        Michael.Hennerich@...log.com, alexandru.ardelean@...log.com,
        jic23@...nel.org, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        lars@...afoo.de, Dragos.Bogdan@...log.com, Darius.Berghe@...log.com
Subject: Re: [PATCH v2 2/2] iio: accel: Add driver support for ADXL355

On Fri, Jul 23, 2021 at 06:44:04PM +0100, Jonathan Cameron wrote:
> Mark Brown <broonie@...nel.org> wrote:

> > > @Mark.  This has come up a few times recently.  Are we now safe to assume
> > > that regmap will always copy data when used with SPI and hence we no
> > > longer need to ensure DMA safe buffers?     

> > Only for single register I/O, I'd not assume that for things like raw
> > I/O.

> Thanks for the confirmation.  So in this driver that means we
> need DMA safe buffers for the regmap_bulk_ calls.  Easiest approach
> is probably to use a __cacheline_aligned buffer at the end of the
> iio_priv() structure.

Yeah, it might be fine depending on the bus/format type but it's not
something you can generally assume.

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