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.
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
