Date:   Tue,  7 Nov 2017 21:52:14 -0600
From:   David Lechner <david@...hnology.com>
To:     dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org
Cc:     David Lechner <david@...hnology.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v1 0/2] DRM driver for ILI9225 display panels

This is a new driver for ILI9225 based display panels.

There are a couple of things that stand out:

1.  Despite my best efforts, I could not find a name for this display[1], so I
    have made up a generic name for it. If someone recognizes this and has a
    name for it, please speak up. The best documentation I could find was
    here[2].

2.  There is quite a bit of one-off code copied from mipi-dbi.c. Based on the
    feedback from a previous patch series, I'm guessing that we don't want to
    modify mipi-dbi.c to accommodate the ILI9225 controller because the ILI9225
    controller does not use standard MIPI commands. ILI9225 has it's own
    non-standard command set, but other than that, it pretty much matches the
    generic mipi-dbi driver in all regards.

    Code that could be easily shared:

    a.  ili9225_buf_copy() is exactly the same as mipi_dbi_buf_copy()
        - ili9225_buf_copy() is used in ili9225_fb_dirty()
        - mipi_dbi_buf_copy() is static in mipi-dbi.c

    b.  ili9225_spi_cmd_max_speed() is exactly the same as
        mipi_dbi_spi_cmd_max_speed()
        - ili9225_spi_cmd_max_speed() is used in ili9225_command() below, so
          would not need to be copied if mipi_dbi_typec3_command() could be
          shared
        - mipi_dbi_spi_cmd_max_speed() is static in mipi-dbi.c

    c.  ili9225_command() is nearly the same as mipi_dbi_typec3_command()
        - a few unused lines were removed so I didn't have to copy even more
          code, but these would not be an issue if code was shared
        - cmd == ILI9225_WRITE_DATA_TO_GRAM instead of
          cmd == MIPI_DCS_WRITE_MEMORY_START

    d.  ili9225_spi_init() is nearly the same as mipi_dbi_spi_init()
        - a few unused lines were removed so I didn't have to copy even more
          code, but these would not be an issue if code was shared
        - mipi->command = ili9225_command instead of
          mipi->command = mipi_dbi_typec3_command
        - this function would not need to be copied if mipi_dbi_typec3_command()
          was modified to work with the ILI9225 command set too

    e.  ili9225_init() is nearly the same as mipi_dbi_init()
        - only difference is ili9225_fb_funcs instead of mipi_dbi_fb_funcs

3.  I haven't tried it, but I believe that it is possible to implement
    DRM_FORMAT_RGB888 directly instead of simulating DRM_FORMAT_XRGB8888.
    I don't know if there would be any real benefit to doing this. I am not
    familiar enough with userspace programs/libraries to know if this mode is
    universally used. And, it will only physically be 18-bit color instead of
    24-bit but will increase the amount of data transferred by 50% (3 bytes per
    pixel instead of 2). Implementing this would have a side effect of making
    the one-off shared code (described above) more than one-off though.

[1]: https://github.com/Nkawu/TFT_22_ILI9225
[2]: http://www.hotmcu.com/22-176x220-tft-lcd-with-spi-interface-p-316.html

David Lechner (2):
  dt-bindings: Add binding for Ilitek ILI9225 display panels
  drm/tinydrm: add driver for ILI9225 panels

 .../devicetree/bindings/display/ilitek,ili9225.txt |  25 +
 MAINTAINERS                                        |   6 +
 drivers/gpu/drm/tinydrm/Kconfig                    |  10 +
 drivers/gpu/drm/tinydrm/Makefile                   |   1 +
 drivers/gpu/drm/tinydrm/ili9225.c                  | 547 +++++++++++++++++++++
 5 files changed, 589 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/ilitek,ili9225.txt
 create mode 100644 drivers/gpu/drm/tinydrm/ili9225.c

--
2.7.4

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