Re: [PATCH v1 0/2] DRM driver for ILI9225 display panels

Hi David, nice to see a new driver.

Den 08.11.2017 04.52, skrev David Lechner:

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.

Yes you're right, I don't want non MIPI code in mipi-dbi, but we can try and make it flexible for usage with DBI like interfaces.

 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

You can export mipi_dbi_buf_copy().

 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

Same here, you can export the function.

 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

Looks like you can use mipi_dbi_spi_init() and reassign afterwards:     mipi_dbi_spi_init();     mipi->command = ili9225_command;

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

When we get framebuffer flushing trough atomic modeset, we'll use a generic fb_dirty and at that point it will be possible to use mipi_dbi_init(). The actual flushing will happen in the update callback I guess.

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.

I have tried it on a display and I couldn't really tell the difference between 16-bit and 18-bit colors, with X windows at least. And as you say it's terrible for the framerate.

I'll look closer through the driver later today and see if I have more comments.

Side note: This controller can also do something called 24-bit 4 wire SPI. It uses a Start byte the same way that the (only) SPI mode on ILI9320 and ILI9325 do. I did a test implementation for ILI9325 where I used regmap as the register abstraction: https://github.com/notro/tinydrm/blob/master/tinydrm-ili9325.c

Noralf.

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