[SRU][Q][PATCH 3/9] drm/i915/dp: Export helper to determine if FEC on non-UHBR links is required

[AceLan Kao]

From: Imre Deak <imre.deak at intel.com>

BugLink: https://bugs.launchpad.net/bugs/2131066

Export the helper function to determine if FEC is required on a non-UHBR
(8b10b) SST or MST link. A follow up change will take this into use for
MST as well.

While at it determine the output type from the CRTC state, which allows
dropping the intel_dp argument. Also make the function return the
required FEC state, instead of setting this in the CRTC state, which
allows only querying this requirement, without changing the state.

Also rename the function to intel_dp_needs_8b10b_fec(), to clarify that
the function determines if FEC is required on an 8b10b link (on 128b132b
links FEC is always enabled by the HW implicitly, so the function will
return false for that case).

Signed-off-by: Imre Deak <imre.deak at intel.com>
Reviewed-by: Jouni Högander <jouni.hogander at intel.com>
Link: https://lore.kernel.org/r/20251015161934.262108-4-imre.deak@intel.com
(cherry picked from commit cb6c8f1f6f46ac2cbfb42ce8eb8b18257aeaa91a)
Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao at canonical.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c     | 21 +++++++++++++--------
 drivers/gpu/drm/i915/display/intel_dp.h     |  2 ++
 drivers/gpu/drm/i915/display/intel_dp_mst.c |  2 +-
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 62efa857cb7a2..eeabcd3d07ef3 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2338,24 +2338,29 @@ static int intel_edp_dsc_compute_pipe_bpp(struct intel_dp *intel_dp,
 	return 0;
 }
 
-static void intel_dp_fec_compute_config(struct intel_dp *intel_dp,
-					struct intel_crtc_state *crtc_state)
+/*
+ * Return whether FEC must be enabled for 8b10b SST or MST links. On 128b132b
+ * links FEC is always enabled implicitly by the HW, so this function returns
+ * false for that case.
+ */
+bool intel_dp_needs_8b10b_fec(const struct intel_crtc_state *crtc_state,
+			      bool dsc_enabled_on_crtc)
 {
 	if (intel_dp_is_uhbr(crtc_state))
-		return;
+		return false;
 
 	if (crtc_state->fec_enable)
-		return;
+		return true;
 
 	/*
 	 * Though eDP v1.5 supports FEC with DSC, unlike DP, it is optional.
 	 * Since, FEC is a bandwidth overhead, continue to not enable it for
 	 * eDP. Until, there is a good reason to do so.
 	 */
-	if (intel_dp_is_edp(intel_dp))
-		return;
+	if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_EDP))
+		return false;
 
-	crtc_state->fec_enable = true;
+	return dsc_enabled_on_crtc;
 }
 
 int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
@@ -2377,7 +2382,7 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 	 * FIXME: set the FEC enabled state once pipe_config->port_clock is
 	 * already known, so the UHBR/non-UHBR mode can be determined.
 	 */
-	intel_dp_fec_compute_config(intel_dp, pipe_config);
+	pipe_config->fec_enable = intel_dp_needs_8b10b_fec(pipe_config, true);
 
 	if (!intel_dp_dsc_supports_format(connector, pipe_config->output_format))
 		return -EINVAL;
diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
index 0657f56811966..95e50e888b2f4 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.h
+++ b/drivers/gpu/drm/i915/display/intel_dp.h
@@ -72,6 +72,8 @@ void intel_dp_encoder_flush_work(struct drm_encoder *encoder);
 int intel_dp_compute_config(struct intel_encoder *encoder,
 			    struct intel_crtc_state *pipe_config,
 			    struct drm_connector_state *conn_state);
+bool intel_dp_needs_8b10b_fec(const struct intel_crtc_state *crtc_state,
+			      bool dsc_enabled_on_crtc);
 int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 				struct intel_crtc_state *pipe_config,
 				struct drm_connector_state *conn_state,
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 6666b7361c186..7db28f2dd996a 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -296,7 +296,7 @@ int intel_dp_mtp_tu_compute_config(struct intel_dp *intel_dp,
 	/*
 	 * NOTE: The following must reset crtc_state->fec_enable for UHBR/DSC
 	 * after it was set by intel_dp_dsc_compute_config() ->
-	 * intel_dp_fec_compute_config().
+	 * intel_dp_needs_8b10b_fec().
 	 */
 	if (dsc) {
 		if (!intel_dp_supports_fec(intel_dp, connector, crtc_state))
-- 
2.43.0