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

Marcus Weseloh mweseloh42 at gmail.com
Thu Nov 19 07:53:41 PST 2015

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 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(+)


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