On Mon, Jun 03, 2024 at 01:21:35PM +0200, Noralf Trønnes via B4 Relay wrote:
> From: Noralf Trønnes <noralf@xxxxxxxxxxx>
>
> 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.
>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_mipi_dbi.c | 29 +++++++++++++++++++++++++----
> include/drm/drm_mipi_dbi.h | 5 +++++
> 2 files changed, 30 insertions(+), 4 deletions(-)
The patch generally LGTM. The only nit is the name of
'emulation_format'. My first impression was that it is a format that the
driver is emulating to userspace, however it looks like this is
over-the-wire format (with the RGB666 vs RGB888 note kept in mind).
If my understanding is correct, I'd suggest renaming emulation_format
to something like 'raw_format' or 'panel_format'.
>
> diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
> index 77f8a828d6e0..eb330676857c 100644
> --- a/drivers/gpu/drm/drm_mipi_dbi.c
> +++ b/drivers/gpu/drm/drm_mipi_dbi.c
> @@ -206,6 +206,7 @@ int mipi_dbi_buf_copy(void *dst, struct iosys_map *src, struct drm_framebuffer *
> struct drm_rect *clip, bool swap,
> struct drm_format_conv_state *fmtcnv_state)
> {
> + struct mipi_dbi_dev *dbidev = drm_to_mipi_dbi_dev(fb->dev);
> struct drm_gem_object *gem = drm_gem_fb_get_obj(fb, 0);
> struct iosys_map dst_map = IOSYS_MAP_INIT_VADDR(dst);
> int ret;
> @@ -222,8 +223,18 @@ int mipi_dbi_buf_copy(void *dst, struct iosys_map *src, struct drm_framebuffer *
> else
> drm_fb_memcpy(&dst_map, NULL, src, fb, clip);
> break;
> + case DRM_FORMAT_RGB888:
> + drm_fb_memcpy(&dst_map, NULL, src, fb, clip);
> + break;
> case DRM_FORMAT_XRGB8888:
> - drm_fb_xrgb8888_to_rgb565(&dst_map, NULL, src, fb, clip, fmtcnv_state, swap);
> + switch (dbidev->emulation_format) {
> + case DRM_FORMAT_RGB565:
> + drm_fb_xrgb8888_to_rgb565(&dst_map, NULL, src, fb, clip, fmtcnv_state, swap);
> + break;
> + case DRM_FORMAT_RGB888:
> + drm_fb_xrgb8888_to_rgb888(&dst_map, NULL, src, fb, clip, fmtcnv_state);
> + break;
> + }
> break;
> default:
> drm_err_once(fb->dev, "Format is not supported: %p4cc\n",
[skipped]
> diff --git a/include/drm/drm_mipi_dbi.h b/include/drm/drm_mipi_dbi.h
> index b36596efdcc3..85bf19b98cee 100644
> --- a/include/drm/drm_mipi_dbi.h
> +++ b/include/drm/drm_mipi_dbi.h
> @@ -101,6 +101,11 @@ struct mipi_dbi_dev {
> */
> struct drm_display_mode mode;
>
> + /**
> + * @emulation_format: Pixel format to use when emulating XRGB8888
> + */
> + u32 emulation_format;
> +
> /**
> * @tx_buf: Buffer used for transfer (copy clip rect area)
> */
>
> --
> 2.45.1
>
>
--
With best wishes
Dmitry
