> -----Original Message-----
> From: andrescj via sendgmr <[email protected]>
> On Behalf Of Andres Calderon Jaramillo
> Sent: Tuesday, December 15, 2020 3:50 AM
> To: [email protected]
> Cc: Shankar, Uma <[email protected]>; Venkatesh Reddy, Sushma
> <[email protected]>; [email protected]; Andres
> Calderon Jaramillo <[email protected]>
> Subject: [PATCH] drm/i915/display: Prevent double YUV range correction on HDR
> planes
>
> From: Andres Calderon Jaramillo <[email protected]>
>
> Prevent the ICL HDR plane pipeline from performing YUV color range correction
> twice when the input is in limited range.
>
> Before this patch the following could happen: user space gives us a YUV
> buffer in
> limited range; per the pipeline in [1], the plane would first go through a
> "YUV
> Range correct" stage that expands the range; the plane would then go through
> the "Input CSC" stage which would also expand the range because
> icl_program_input_csc() would use a matrix and an offset that assume limited-
> range input; this would ultimately cause dark and light colors to appear
> darker
> and lighter than they should respectively.
>
> This is an issue because if a buffer switches between being scanned out and
> being composited with the GPU, the user will see a color difference.
> If this switching happens quickly and frequently, the user will perceive this
> as a
> flickering.
>
> [1] https://01.org/sites/default/files/documentation/intel-gfx-prm-osrc-icllp-
> vol12-displayengine_0.pdf#page=281
Change looks good to me, double conversion should not be done.
Plane input csc coefficients take care of the limited range.
Reviewed-by: Uma Shankar <[email protected]>
> Signed-off-by: Andres Calderon Jaramillo <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> b/drivers/gpu/drm/i915/display/intel_display.c
> index 761be8deaa9b..aeea344b06ad 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -4811,6 +4811,13 @@ u32 glk_plane_color_ctl(const struct intel_crtc_state
> *crtc_state,
> plane_color_ctl |=
> PLANE_COLOR_YUV_RANGE_CORRECTION_DISABLE;
> } else if (fb->format->is_yuv) {
> plane_color_ctl |= PLANE_COLOR_INPUT_CSC_ENABLE;
> +
> + /*
> + * Disable the YUV range correction stage because the input CSC
> + * stage already takes care of range conversion by using
> separate
> + * matrices and offsets depending on the color range.
> + */
> + plane_color_ctl |=
> PLANE_COLOR_YUV_RANGE_CORRECTION_DISABLE;
> }
>
> return plane_color_ctl;
> --
> 2.29.2.684.gfbc64c5ab5-goog
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