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DRM_FORMAT_RGB888 is 24 bits per pixel and it would be natural to send it on the SPI bus using a 24 bits per word transfer. The problem with this is that not all SPI controllers support 24 bpw. Since DRM_FORMAT_RGB888 is stored in memory as little endian and the SPI bus is big endian we use 8 bpw to always get the same pixel format on the bus: b8g8r8. The MIPI DCS specification lists the standard commands that can be sent over the MIPI DBI interface. The set_address_mode (36h) command has one bit in the parameter that controls RGB/BGR order. This means that the controller can be configured to receive the pixel as BGR. RGB888 is rarely supported on these controllers but RGB666 is very common. All datasheets I have seen do at least support the pixel format option where each color is sent as one byte and the 6 MSB's are used. All this put together means that we can send each pixel as b8g8r8 and an RGB666 capable controller sees this as b6x2g6x2r6x2. v4: - s/emulation_format/pixel_format/ (Dmitry) Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> Link: https://patchwork.freedesktop.org/patch/msgid/20240604-panel-mipi-dbi-rgb666-v4-4-d7c2bcb9b78d@tronnes.org Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.