drm/mipi-dbi: Add support for DRM_FORMAT_RGB888

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>

diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
index 77f8a828d6e0425134184c68886b2b1905b0e7f4..1661190c29a2500b525074fa622eb9a5952be304 100644 (file)
--- 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->pixel_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",
@@ -260,9 +271,11 @@ static void mipi_dbi_fb_dirty(struct iosys_map *src, struct drm_framebuffer *fb,
        struct mipi_dbi_dev *dbidev = drm_to_mipi_dbi_dev(fb->dev);
        unsigned int height = rect->y2 - rect->y1;
        unsigned int width = rect->x2 - rect->x1;
+       const struct drm_format_info *dst_format;
        struct mipi_dbi *dbi = &dbidev->dbi;
        bool swap = dbi->swap_bytes;
        int ret = 0;
+       size_t len;
        bool full;
        void *tr;
 
@@ -283,8 +296,13 @@ static void mipi_dbi_fb_dirty(struct iosys_map *src, struct drm_framebuffer *fb,
        mipi_dbi_set_window_address(dbidev, rect->x1, rect->x2 - 1, rect->y1,
                                    rect->y2 - 1);
 
-       ret = mipi_dbi_command_buf(dbi, MIPI_DCS_WRITE_MEMORY_START, tr,
-                                  width * height * 2);
+       if (fb->format->format == DRM_FORMAT_XRGB8888)
+               dst_format = drm_format_info(dbidev->pixel_format);
+       else
+               dst_format = fb->format;
+       len = drm_format_info_min_pitch(dst_format, 0, width) * height;
+
+       ret = mipi_dbi_command_buf(dbi, MIPI_DCS_WRITE_MEMORY_START, tr, len);
 err_msg:
        if (ret)
                drm_err_once(fb->dev, "Failed to update display %d\n", ret);
@@ -572,7 +590,7 @@ static const uint32_t mipi_dbi_formats[] = {
  * has one fixed &drm_display_mode which is rotated according to @rotation.
  * This mode is used to set the mode config min/max width/height properties.
  *
- * Use mipi_dbi_dev_init() if you don't need custom formats.
+ * Use mipi_dbi_dev_init() if you want native RGB565 and emulated XRGB8888 format.
  *
  * Note:
  * Some of the helper functions expects RGB565 to be the default format and the
@@ -631,6 +649,9 @@ int mipi_dbi_dev_init_with_formats(struct mipi_dbi_dev *dbidev,
        drm->mode_config.min_height = dbidev->mode.vdisplay;
        drm->mode_config.max_height = dbidev->mode.vdisplay;
        dbidev->rotation = rotation;
+       dbidev->pixel_format = formats[0];
+       if (formats[0] == DRM_FORMAT_RGB888)
+               dbidev->dbi.write_memory_bpw = 8;
 
        DRM_DEBUG_KMS("rotation = %u\n", rotation);
 

diff --git a/include/drm/drm_mipi_dbi.h b/include/drm/drm_mipi_dbi.h
index b36596efdcc36c5e9a71d781adf0556c3ec058e3..f45f9612c0bc49b3ae50b3f8f891d1913103a116 100644 (file)
--- 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;
 
+       /**
+        * @pixel_format: Native pixel format (DRM_FORMAT\_\*)
+        */
+       u32 pixel_format;
+
        /**
         * @tx_buf: Buffer used for transfer (copy clip rect area)
         */