[PATCH 5/5] drm/solomon: Add SSD130x OLED displays SPI support

[Mark Brown]

On Thu, Apr 07, 2022 at 10:02:04PM +0200, Javier Martinez Canillas wrote:
> The ssd130x driver only provides the core support for these devices but it
> does not have any bus transport logic. Add a driver to interface over SPI.
> 
> There is a difference in the communication protocol when using 4-wire SPI
> instead of I2C. For the latter, a control byte that contains a D/C# field
> has to be sent. This field tells the controller whether the data has to be
> written to the command register or to the graphics display data memory.
> 
> But for 4-wire SPI that control byte is not used, instead a real D/C# line
> must be pulled HIGH for commands data and LOW for graphics display data.
> 
> For this reason the standard SPI regmap can't be used and a custom .write
> bus handler is needed.

Acked-by: Mark Brown <broonie at kernel.org>
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