drm/i915/dp_mst: Track DSC enabled status on the MST link

Track whether DSC is enabled on any CRTC on a link. On DP-SST (and DSI)
this will always match the CRTC's DSC state, those links having only a
single stream (aka CRTC). For instance, on DP-MST if DSC is enabled for
CRTC#0, but disabled for CRTC#1, the DSC/FEC state for these CRTCs will
be as follows:

CRTC#0:
 - compression_enable = true
 - compression_enabled_on_link = true
 - fec_enable = true for 8b10b, false for 128b132b

CRTC#1:
 - compression_enable = false
 - compression_enabled_on_link = true
 - fec_enable = true for 8b10b, false for 128b132b

This patch only sets compression_enabled_on_link for CRTC#0 above and
enables FEC on CRTC#0 if DSC was enabled on any other CRTC on the 8b10b
MST link. A follow-up change will make sure that the state of all the
CRTCs (CRTC#1 above) on an MST link is recomputed if DSC gets enabled on
any CRTC, setting compression_enabled_on_link and fec_enable for these.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://lore.kernel.org/r/20251015161934.262108-6-imre.deak@intel.com

4 files changed, 15 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 203dd38a9ec4..20747fa4d3da 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -1279,6 +1279,8 @@ struct intel_crtc_state {
 
 	/* Display Stream compression state */
 	struct {
+		/* Only used for state computation, not read out from the HW. */
+		bool compression_enabled_on_link;
 		bool compression_enable;
 		int num_streams;
 		/* Compressed Bpp in U6.4 format (first 4 bits for fractional part) */
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 844118735998..95884af242b3 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2387,7 +2387,7 @@ bool intel_dp_needs_8b10b_fec(const struct intel_crtc_state *crtc_state,
 	if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_EDP))
 		return false;
 
-	return dsc_enabled_on_crtc;
+	return dsc_enabled_on_crtc || intel_dsc_enabled_on_link(crtc_state);
 }
 
 int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c b/drivers/gpu/drm/i915/display/intel_vdsc.c
index 803f3b395c79..dbf2cf1b896d 100644
--- a/drivers/gpu/drm/i915/display/intel_vdsc.c
+++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
@@ -374,9 +374,20 @@ int intel_dsc_compute_params(struct intel_crtc_state *pipe_config)
 
 void intel_dsc_enable_on_crtc(struct intel_crtc_state *crtc_state)
 {
+	crtc_state->dsc.compression_enabled_on_link = true;
 	crtc_state->dsc.compression_enable = true;
 }
 
+bool intel_dsc_enabled_on_link(const struct intel_crtc_state *crtc_state)
+{
+	struct intel_display *display = to_intel_display(crtc_state);
+
+	drm_WARN_ON(display->drm, crtc_state->dsc.compression_enable &&
+		    !crtc_state->dsc.compression_enabled_on_link);
+
+	return crtc_state->dsc.compression_enabled_on_link;
+}
+
 enum intel_display_power_domain
 intel_dsc_power_domain(struct intel_crtc *crtc, enum transcoder cpu_transcoder)
 {
diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.h b/drivers/gpu/drm/i915/display/intel_vdsc.h
index 8c7c7fb652c3..99f64ac54b27 100644
--- a/drivers/gpu/drm/i915/display/intel_vdsc.h
+++ b/drivers/gpu/drm/i915/display/intel_vdsc.h
@@ -21,6 +21,7 @@ void intel_dsc_enable(const struct intel_crtc_state *crtc_state);
 void intel_dsc_disable(const struct intel_crtc_state *crtc_state);
 int intel_dsc_compute_params(struct intel_crtc_state *pipe_config);
 void intel_dsc_enable_on_crtc(struct intel_crtc_state *crtc_state);
+bool intel_dsc_enabled_on_link(const struct intel_crtc_state *crtc_state);
 void intel_dsc_get_config(struct intel_crtc_state *crtc_state);
 enum intel_display_power_domain
 intel_dsc_power_domain(struct intel_crtc *crtc, enum transcoder cpu_transcoder);