> -----Original Message-----
> From: Intel-gfx <intel-gfx-boun...@lists.freedesktop.org> On Behalf Of Ville 
> Syrjala
> Sent: Monday, November 14, 2022 9:07 PM
> To: intel-gfx@lists.freedesktop.org
> Subject: [Intel-gfx] [PATCH v3 17/20] drm/i915: Use hw degamma LUT for sw
> gamma on glk with YCbCr output
> 
> From: Ville Syrjälä <ville.syrj...@linux.intel.com>
> 
> On glk we can no longer reorder the hw LUTS vs. pipe CSC like we could on 
> eaerlier

Typo in "earlier"

> platforms, and neither do we have a separate output CSC like on icl+. That 
> means if
> we use the pipe CSC for YCbCr output we are currently applying the gamma LUT
> after the RGB->YCbCr conversion, which is just wrong.
> The further we go from a linear curve the more distorted the resulting colors
> become.
> 
> To work around this terrible limitation the best we can do is repurpose the hw
> degamma LUT as a poor man's gamma LUT. Now that we have the internal
> pre_csc_lut attachment point that is not particularly hard to do.
> 
> What makes this less than ideal however is the fact that the hw degamma LUT 
> and
> gamma LUTs have very different capabilities.
> The gamma LUT can operatie in direct color type modes, whereas the degamma LUT
> can't and just always operaters in interpolated mode. Additionally the 
> degamma LUT

Typo in "operate"

> is just a single 1D LUT, whereas the gamma LUT is made of three separate 1D 
> LUts
> (one for each channel).
> So in order to make this semi-sensible we must also verify the user supplied 
> LUT
> more less matches the hw degamma LUT capabilities.
> We still end up losing most of the LUT entries though, so the results might 
> be a bit
> crap.
> 
> The other option of flat out rejecting the YCbCr+gamma LUT combo seems
> extremely likely to just cause a black screen for the user.
> Eg. pretty sure Xorg always applies some kind of gamma LUT, and if the user 
> then
> plugs in a display that needs YCbCr output we're toast.

With the typos fixed, this looks good to me.
Reviewed-by: Uma Shankar <uma.shan...@intel.com>

> Signed-off-by: Ville Syrjälä <ville.syrj...@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_color.c | 61 +++++++++++++++++++---
>  1 file changed, 54 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_color.c
> b/drivers/gpu/drm/i915/display/intel_color.c
> index 8bb8983b490c..c336524d9225 100644
> --- a/drivers/gpu/drm/i915/display/intel_color.c
> +++ b/drivers/gpu/drm/i915/display/intel_color.c
> @@ -1362,13 +1362,13 @@ static int check_lut_size(const struct
> drm_property_blob *lut, int expected)
>       return 0;
>  }
> 
> -static int check_luts(const struct intel_crtc_state *crtc_state)
> +static int _check_luts(const struct intel_crtc_state *crtc_state,
> +                    u32 degamma_tests, u32 gamma_tests)
>  {
>       struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
>       const struct drm_property_blob *gamma_lut = crtc_state->hw.gamma_lut;
>       const struct drm_property_blob *degamma_lut = crtc_state-
> >hw.degamma_lut;
>       int gamma_length, degamma_length;
> -     u32 gamma_tests, degamma_tests;
> 
>       /* C8 relies on its palette being stored in the legacy LUT */
>       if (crtc_state->c8_planes && !lut_is_legacy(crtc_state->hw.gamma_lut)) {
> @@ -1379,8 +1379,6 @@ static int check_luts(const struct intel_crtc_state
> *crtc_state)
> 
>       degamma_length = intel_degamma_lut_size(crtc_state);
>       gamma_length = intel_gamma_lut_size(crtc_state);
> -     degamma_tests = intel_degamma_lut_tests(crtc_state);
> -     gamma_tests = intel_gamma_lut_tests(crtc_state);
> 
>       if (check_lut_size(degamma_lut, degamma_length) ||
>           check_lut_size(gamma_lut, gamma_length)) @@ -1393,6 +1391,13 @@
> static int check_luts(const struct intel_crtc_state *crtc_state)
>       return 0;
>  }
> 
> +static int check_luts(const struct intel_crtc_state *crtc_state) {
> +     return _check_luts(crtc_state,
> +                        intel_degamma_lut_tests(crtc_state),
> +                        intel_gamma_lut_tests(crtc_state));
> +}
> +
>  static u32 i9xx_gamma_mode(struct intel_crtc_state *crtc_state)  {
>       if (!crtc_state->gamma_enable ||
> @@ -1414,9 +1419,11 @@ void intel_color_assert_luts(const struct 
> intel_crtc_state
> *crtc_state)
>                           crtc_state->post_csc_lut != 
> crtc_state->hw.gamma_lut);
>       } else if (DISPLAY_VER(i915) == 10) {
>               drm_WARN_ON(&i915->drm,
> +                         crtc_state->post_csc_lut == crtc_state->hw.gamma_lut
> &&
>                           crtc_state->pre_csc_lut != 
> crtc_state->hw.degamma_lut
> &&
>                           crtc_state->pre_csc_lut != i915-
> >display.color.glk_linear_degamma_lut);
>               drm_WARN_ON(&i915->drm,
> +                         crtc_state->post_csc_lut != NULL &&
>                           crtc_state->post_csc_lut != 
> crtc_state->hw.gamma_lut);
>       } else if (crtc_state->gamma_mode != GAMMA_MODE_MODE_SPLIT) {
>               drm_WARN_ON(&i915->drm,
> @@ -1728,10 +1735,33 @@ static u32 glk_gamma_mode(const struct
> intel_crtc_state *crtc_state)
>               return GAMMA_MODE_MODE_10BIT;
>  }
> 
> -static void glk_assign_luts(struct intel_crtc_state *crtc_state)
> +static bool glk_use_pre_csc_lut_for_gamma(const struct intel_crtc_state
> +*crtc_state) {
> +     return crtc_state->hw.gamma_lut &&
> +             !crtc_state->c8_planes &&
> +             crtc_state->output_format != INTEL_OUTPUT_FORMAT_RGB; }
> +
> +static int glk_assign_luts(struct intel_crtc_state *crtc_state)
>  {
>       struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
> 
> +     if (glk_use_pre_csc_lut_for_gamma(crtc_state)) {
> +             struct drm_property_blob *gamma_lut;
> +
> +             gamma_lut = create_resized_lut(i915, crtc_state->hw.gamma_lut,
> +                                            INTEL_INFO(i915)-
> >display.color.degamma_lut_size);
> +             if (IS_ERR(gamma_lut))
> +                     return PTR_ERR(gamma_lut);
> +
> +             drm_property_replace_blob(&crtc_state->pre_csc_lut, gamma_lut);
> +             drm_property_replace_blob(&crtc_state->post_csc_lut, NULL);
> +
> +             drm_property_blob_put(gamma_lut);
> +
> +             return 0;
> +     }
> +
>       intel_assign_luts(crtc_state);
> 
>       /*
> @@ -1743,6 +1773,19 @@ static void glk_assign_luts(struct intel_crtc_state
> *crtc_state)
>       if (crtc_state->csc_enable && !crtc_state->pre_csc_lut)
>               drm_property_replace_blob(&crtc_state->pre_csc_lut,
>                                         i915-
> >display.color.glk_linear_degamma_lut);
> +
> +     return 0;
> +}
> +
> +static int glk_check_luts(const struct intel_crtc_state *crtc_state) {
> +     u32 degamma_tests = intel_degamma_lut_tests(crtc_state);
> +     u32 gamma_tests = intel_gamma_lut_tests(crtc_state);
> +
> +     if (glk_use_pre_csc_lut_for_gamma(crtc_state))
> +             gamma_tests |= degamma_tests;
> +
> +     return _check_luts(crtc_state, degamma_tests, gamma_tests);
>  }
> 
>  static int glk_color_check(struct intel_crtc_state *crtc_state) @@ -1750,7 
> +1793,7
> @@ static int glk_color_check(struct intel_crtc_state *crtc_state)
>       struct drm_i915_private *i915 = to_i915(crtc_state->uapi.crtc->dev);
>       int ret;
> 
> -     ret = check_luts(crtc_state);
> +     ret = glk_check_luts(crtc_state);
>       if (ret)
>               return ret;
> 
> @@ -1769,11 +1812,13 @@ static int glk_color_check(struct intel_crtc_state
> *crtc_state)
>       }
> 
>       crtc_state->gamma_enable =
> +             !glk_use_pre_csc_lut_for_gamma(crtc_state) &&
>               crtc_state->hw.gamma_lut &&
>               !crtc_state->c8_planes;
> 
>       /* On GLK+ degamma LUT is controlled by csc_enable */
>       crtc_state->csc_enable =
> +             glk_use_pre_csc_lut_for_gamma(crtc_state) ||
>               crtc_state->hw.degamma_lut ||
>               crtc_state->output_format != INTEL_OUTPUT_FORMAT_RGB ||
>               crtc_state->hw.ctm || crtc_state->limited_color_range; @@ -
> 1786,7 +1831,9 @@ static int glk_color_check(struct intel_crtc_state 
> *crtc_state)
>       if (ret)
>               return ret;
> 
> -     glk_assign_luts(crtc_state);
> +     ret = glk_assign_luts(crtc_state);
> +     if (ret)
> +             return ret;
> 
>       crtc_state->preload_luts = intel_can_preload_luts(crtc_state);
> 
> --
> 2.37.4

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