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

[Daniel Vetter]

On Mon, Jan 24, 2022 at 05:18:07PM -0500, Alex Deucher wrote:
> On Mon, Jan 24, 2022 at 5:16 PM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> >
> > 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
> > 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.pinchart at ideasonboard.com>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > Cc: Geert Uytterhoeven <geert at linux-m68k.org>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > Cc: Maxime Ripard <mripard at kernel.org>
> > Cc: Thomas Zimmermann <tzimmermann at suse.de>
> > Cc: David Airlie <airlied at linux.ie>
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> 
> Reviewed-by: Alex Deucher <alexander.deucher at amd.com>

Thanks for taking a look, pushed to drm-misc-next.
-Daniel

> 
> > ---
> >  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;
> >
> > @@ -1075,12 +1079,18 @@ struct drm_crtc {
> >         /**
> >          * @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;
> >
> > --
> > 2.33.0
> >

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch