> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of Ville Syrjala
> Sent: Monday, November 14, 2022 9:07 PM
> To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Subject: [PATCH v3 17/20] drm/i915: Use hw degamma LUT for sw
> gamma on glk with YCbCr output
>
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> 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.shankar@xxxxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> 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
