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drm/color-mgmt: Prepare for RGB332 palettes

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Add helper drm_crtc_fill_palette_332(), which fills palettes with
RGB332 color data. Each color in RGB332 format serves as an index
into an 8-bit palette that stores the corresponding component-based
colors.

Vesadrm will use the new helper to emulate RGB formats on top of
framebuffers in C8 format.

v2:
- add comments on bit operations (Javier)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20250714151513.309475-6-tzimmermann@suse.de
This commit is contained in:
Thomas Zimmermann
2025-07-14 17:13:05 +02:00
parent 061963cd9e
commit 7ff61177b7
2 changed files with 35 additions and 0 deletions
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34
drivers/gpu/drm/drm_color_mgmt.c
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@@ -817,6 +817,40 @@ void drm_crtc_load_palette_8(struct drm_crtc *crtc, const struct drm_color_lut *
}
EXPORT_SYMBOL(drm_crtc_load_palette_8);
static void fill_palette_332(struct drm_crtc *crtc, u16 r, u16 g, u16 b,
drm_crtc_set_lut_func set_palette)
{
unsigned int i = (r << 5) | (g << 2) | b; /* 8-bit palette index */
/* Expand R (3-bit) G (3-bit) and B (2-bit) values to 16-bit values */
r = (r << 13) | (r << 10) | (r << 7) | (r << 4) | (r << 1) | (r >> 2);
g = (g << 13) | (g << 10) | (g << 7) | (g << 4) | (g << 1) | (g >> 2);
b = (b << 14) | (b << 12) | (b << 10) | (b << 8) | (b << 6) | (b << 4) | (b << 2) | b;
set_palette(crtc, i, r, g, b);
}
/**
* drm_crtc_fill_palette_332 - Programs a default palette for R332-like formats
* @crtc: The displaying CRTC
* @set_palette: Callback for programming the hardware gamma LUT
*
* Programs an RGB332 palette to hardware.
*/
void drm_crtc_fill_palette_332(struct drm_crtc *crtc, drm_crtc_set_lut_func set_palette)
{
unsigned int r, g, b;
/* Limits of 8-8-4 are the maximum number of values for each channel. */
for (r = 0; r < 8; ++r) {
for (g = 0; g < 8; ++g) {
for (b = 0; b < 4; ++b)
fill_palette_332(crtc, r, g, b, set_palette);
}
}
}
EXPORT_SYMBOL(drm_crtc_fill_palette_332);
static void fill_palette_8(struct drm_crtc *crtc, unsigned int i,
drm_crtc_set_lut_func set_palette)
{

1
include/drm/drm_color_mgmt.h
View File

@@ -143,6 +143,7 @@ void drm_crtc_fill_gamma_555(struct drm_crtc *crtc, drm_crtc_set_lut_func set_ga
void drm_crtc_load_palette_8(struct drm_crtc *crtc, const struct drm_color_lut *lut,
drm_crtc_set_lut_func set_palette);
void drm_crtc_fill_palette_332(struct drm_crtc *crtc, drm_crtc_set_lut_func set_palette);
void drm_crtc_fill_palette_8(struct drm_crtc *crtc, drm_crtc_set_lut_func set_palette);
#endif