Re: [PATCH] drm/docs: Document where the C8 color lut is stored

[Thomas Zimmermann]

Hi

Am 24.01.22 um 23:16 schrieb Daniel Vetter:

Also add notes that for atomic drivers it's really somewhere else and
no longer in struct drm_crtc.

Maybe we should put a bigger warning here that this is confusing,
since the pixel format is a plane property, but the GAMMA_LUT property
is on the crtc. But I think we can fix this if/when someone finds a
need for a per-plane CLUT, since I'm not sure such hw even exists. I'm

Best regards
Thomas

Older HW has cursor planes with separate palettes; 16 colors on Matrox IIRC. Not very useful for us, though.

also not sure whether even hardware with a CLUT and a full color
correction pipeline with degamm/cgm/gamma exists.

Motivated by comments from Geert that we have a gap here.

v2: More names for color luts (Laurent).

Cc: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
Cc: Geert Uytterhoeven <ge...@linux-m68k.org>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Cc: Maxime Ripard <mrip...@kernel.org>
Cc: Thomas Zimmermann <tzimmerm...@suse.de>
Cc: David Airlie <airl...@linux.ie>
Cc: Daniel Vetter <dan...@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vet...@intel.com>
---
  drivers/gpu/drm/drm_color_mgmt.c |  4 ++++
  include/drm/drm_crtc.h           | 10 ++++++++++
  2 files changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index bb14f488c8f6..9079fbe21d2f 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -82,6 +82,10 @@
   *    driver boot-up state too. Drivers can access this blob through
   *    &drm_crtc_state.gamma_lut.
   *
+ *     Note that for mostly historical reasons stemming from Xorg heritage,
+ *     this is also used to store the color map (also sometimes color lut, CLUT
+ *     or color palette) for indexed formats like DRM_FORMAT_C8.
+ *
   * “GAMMA_LUT_SIZE”:
   *    Unsigned range property to give the size of the lookup table to be set
   *    on the GAMMA_LUT property (the size depends on the underlying hardware).
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 4d01b4d89775..a70baea0636c 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -285,6 +285,10 @@ struct drm_crtc_state {
         * Lookup table for converting pixel data after the color conversion
         * matrix @ctm.  See drm_crtc_enable_color_mgmt(). The blob (if not
         * NULL) is an array of &struct drm_color_lut.
+        *
+        * Note that for mostly historical reasons stemming from Xorg heritage,
+        * this is also used to store the color map (also sometimes color lut,
+        * CLUT or color palette) for indexed formats like DRM_FORMAT_C8.
         */
        struct drm_property_blob *gamma_lut;

        /**
         * @gamma_size: Size of legacy gamma ramp reported to userspace. Set up
         * by calling drm_mode_crtc_set_gamma_size().
+        *
+        * Note that atomic drivers need to instead use
+        * &drm_crtc_state.gamma_lut. See drm_crtc_enable_color_mgmt().
         */
        uint32_t gamma_size;

         * @gamma_store: Gamma ramp values used by the legacy SETGAMMA and
         * GETGAMMA IOCTls. Set up by calling drm_mode_crtc_set_gamma_size().
+        *
+        * Note that atomic drivers need to instead use
+        * &drm_crtc_state.gamma_lut. See drm_crtc_enable_color_mgmt().
         */
        uint16_t *gamma_store;

@@ -1075,12 +1079,18 @@ struct drm_crtc { /**

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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