linux-kernel - [PATCH] spi: dts: sun4i: Add support for inter-word wait cycles

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Date:	Thu, 19 Nov 2015 16:53:41 +0100
From:	Marcus Weseloh <mweseloh42@...il.com>
To:	linux-sunxi@...glegroups.com
Cc:	Marcus Weseloh <mweseloh42@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Mark Brown <broonie@...nel.org>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-spi@...r.kernel.org
Subject: [PATCH] spi: dts: sun4i: Add support for inter-word wait cycles

Hi all,

the Allwinner A10/A20 SPI module supports an option to configure a number of
clock periods to wait between each word ("SPI Wait Clock Register" in the A20
manual). This is a very useful option if talking to devices which specify a
minimum amount of inter-word wait time.

I initially tried to find a way to let SPI protocol drivers specify this
option, but I couldn't find a mechanism to pass additional options to the spi
master. So I took the spi-davinci driver as an example (it implements a very
similiar functionality) and added a new devicetree property.

While testing this patch I noticed that the SPI module always adds a constant
3 clock cycles to the number set in the Wait Clock Register. That number stays
constant across many different baud rates, so I documented it in the
devicetree binding file.

One thing I am unsure of is the device example in the binding
documentation.  I used "example,dummy" as compatible... is this acceptable or
should I use a device/compatible that actually exists somewhere?

Oh... and should I split binding documentation and code changing patch?

Best regards,

  Marcus

Marcus Weseloh (1):
  spi: dts: sun4i: Add support for inter-word wait cycles using the SPI
    Wait Clock Register

 Documentation/devicetree/bindings/spi/spi-sun4i.txt | 11 +++++++++++
 drivers/spi/spi-sun4i.c                             |  7 +++++++
 2 files changed, 18 insertions(+)

-- 
1.9.1

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