> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of Ville Syrjala
> Sent: Thursday, April 13, 2023 10:19 PM
> To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: [PATCH v2 4/7] drm/i915: Always enable CGM CSC on CHV
>
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> On CHV toggling the CGM CSC on/off while the pipe is running leads to underruns.
> Looks like we'd have to do the toggling strictly inside the start_of_vblank-
> frame_start window to avoid this, but that window is less than a scanline so there's
> no way we can guarantee hitting it.
>
> As a workaround let's just leave the CGM CSC permanently enabled.
> Fortunately the CGM gamma/degamma units don't seem to suffer from this malady.
>
> I also tried turning off CGM unit clock gating, but that did not help.
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 | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_color.c
> b/drivers/gpu/drm/i915/display/intel_color.c
> index 63141f4ed372..7a705e7d8776 100644
> --- a/drivers/gpu/drm/i915/display/intel_color.c
> +++ b/drivers/gpu/drm/i915/display/intel_color.c
> @@ -605,6 +605,16 @@ static void chv_cgm_csc_convert_ctm(const struct
> intel_crtc_state *crtc_state,
> csc->coeff[i] = ctm_to_twos_complement(ctm->matrix[i], 4, 12); }
>
> +#define CHV_CGM_CSC_COEFF_1_0 (1 << 12)
> +
> +static const struct intel_csc_matrix chv_cgm_csc_matrix_identity = {
> + .coeff = {
> + CHV_CGM_CSC_COEFF_1_0, 0, 0,
> + 0, CHV_CGM_CSC_COEFF_1_0, 0,
> + 0, 0, CHV_CGM_CSC_COEFF_1_0,
> + },
> +};
> +
> static void chv_load_cgm_csc(struct intel_crtc *crtc,
> const struct intel_csc_matrix *csc) { @@ -667,9 +677,9
> @@ static void chv_assign_csc(struct intel_crtc_state *crtc_state)
>
> chv_cgm_csc_convert_ctm(crtc_state, &crtc_state->csc);
> } else {
> - drm_WARN_ON(&i915->drm, (crtc_state->cgm_mode &
> CGM_PIPE_MODE_CSC) != 0);
> + drm_WARN_ON(&i915->drm, (crtc_state->cgm_mode &
> CGM_PIPE_MODE_CSC) ==
> +0);
>
> - intel_csc_clear(&crtc_state->csc);
> + crtc_state->csc = chv_cgm_csc_matrix_identity;
> }
> }
>
> @@ -2033,6 +2043,13 @@ static u32 chv_cgm_mode(const struct intel_crtc_state
> *crtc_state)
> !lut_is_legacy(crtc_state->hw.gamma_lut))
> cgm_mode |= CGM_PIPE_MODE_GAMMA;
>
> + /*
> + * Toggling the CGM CSC on/off outside of the tiny window
> + * between start of vblank and frame start causes underruns.
> + * Always enable the CGM CSC as a workaround.
> + */
> + cgm_mode |= CGM_PIPE_MODE_CSC;
> +
> return cgm_mode;
> }
>
> --
> 2.39.2
