Check only the eDP or the DP specific DPCD revision depending on the
sink type. Pass the corresponding revision to the function, which allows
getting the DSC caps of a branch device (in an MST topology, which has
its own DPCD and so DPCD revision).

While at it use DP_DPCD_REV_14 instead of open coding it and for clarity
add a separate function to read out the DSC capability on eDP.

v2:
- Use DP_DPCD_REV_14 instead of open coding it. (Stan)
- Check EDP_DCPD_REV/DPCD_REV in a clearer way. (Ville)

Cc: Ville Syrjälä <[email protected]>
Reviewed-by: Stanislav Lisovskiy <[email protected]> (v1)
Signed-off-by: Imre Deak <[email protected]>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 63 +++++++++++++++----------
 1 file changed, 39 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c 
b/drivers/gpu/drm/i915/display/intel_dp.c
index 0ef7cb8134b66..f92dff32a174a 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -3467,7 +3467,23 @@ bool intel_dp_get_colorimetry_status(struct intel_dp 
*intel_dp)
        return dprx & DP_VSC_SDP_EXT_FOR_COLORIMETRY_SUPPORTED;
 }
 
-static void intel_dp_get_dsc_sink_cap(struct intel_dp *intel_dp)
+static void intel_dp_read_dsc_dpcd(struct drm_dp_aux *aux,
+                                  u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
+{
+       if (drm_dp_dpcd_read(aux, DP_DSC_SUPPORT, dsc_dpcd,
+                            DP_DSC_RECEIVER_CAP_SIZE) < 0) {
+               drm_err(aux->drm_dev,
+                       "Failed to read DPCD register 0x%x\n",
+                       DP_DSC_SUPPORT);
+               return;
+       }
+
+       drm_dbg_kms(aux->drm_dev, "DSC DPCD: %*ph\n",
+                   DP_DSC_RECEIVER_CAP_SIZE,
+                   dsc_dpcd);
+}
+
+static void intel_dp_get_dsc_sink_cap(u8 dpcd_rev, struct intel_dp *intel_dp)
 {
        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 
@@ -3480,30 +3496,27 @@ static void intel_dp_get_dsc_sink_cap(struct intel_dp 
*intel_dp)
        /* Clear fec_capable to avoid using stale values */
        intel_dp->fec_capable = 0;
 
-       /* Cache the DSC DPCD if eDP or DP rev >= 1.4 */
-       if (intel_dp->dpcd[DP_DPCD_REV] >= 0x14 ||
-           intel_dp->edp_dpcd[0] >= DP_EDP_14) {
-               if (drm_dp_dpcd_read(&intel_dp->aux, DP_DSC_SUPPORT,
-                                    intel_dp->dsc_dpcd,
-                                    sizeof(intel_dp->dsc_dpcd)) < 0)
-                       drm_err(&i915->drm,
-                               "Failed to read DPCD register 0x%x\n",
-                               DP_DSC_SUPPORT);
+       if (dpcd_rev < DP_DPCD_REV_14)
+               return;
 
-               drm_dbg_kms(&i915->drm, "DSC DPCD: %*ph\n",
-                           (int)sizeof(intel_dp->dsc_dpcd),
-                           intel_dp->dsc_dpcd);
+       intel_dp_read_dsc_dpcd(&intel_dp->aux, intel_dp->dsc_dpcd);
 
-               /* FEC is supported only on DP 1.4 */
-               if (!intel_dp_is_edp(intel_dp) &&
-                   drm_dp_dpcd_readb(&intel_dp->aux, DP_FEC_CAPABILITY,
-                                     &intel_dp->fec_capable) < 0)
-                       drm_err(&i915->drm,
-                               "Failed to read FEC DPCD register\n");
-
-               drm_dbg_kms(&i915->drm, "FEC CAPABILITY: %x\n",
-                           intel_dp->fec_capable);
+       if (drm_dp_dpcd_readb(&intel_dp->aux, DP_FEC_CAPABILITY,
+                             &intel_dp->fec_capable) < 0) {
+               drm_err(&i915->drm, "Failed to read FEC DPCD register\n");
+               return;
        }
+
+       drm_dbg_kms(&i915->drm, "FEC CAPABILITY: %x\n",
+                   intel_dp->fec_capable);
+}
+
+static void intel_edp_get_dsc_sink_cap(u8 edp_dpcd_rev, struct intel_dp 
*intel_dp)
+{
+       if (edp_dpcd_rev < DP_EDP_14)
+               return;
+
+       intel_dp_read_dsc_dpcd(&intel_dp->aux, intel_dp->dsc_dpcd);
 }
 
 static void intel_edp_mso_mode_fixup(struct intel_connector *connector,
@@ -3674,7 +3687,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
 
        /* Read the eDP DSC DPCD registers */
        if (HAS_DSC(dev_priv))
-               intel_dp_get_dsc_sink_cap(intel_dp);
+               intel_edp_get_dsc_sink_cap(intel_dp->edp_dpcd[0],
+                                          intel_dp);
 
        /*
         * If needed, program our source OUI so we can make various 
Intel-specific AUX services
@@ -5384,7 +5398,8 @@ intel_dp_detect(struct drm_connector *connector,
 
        /* Read DP Sink DSC Cap DPCD regs for DP v1.4 */
        if (HAS_DSC(dev_priv))
-               intel_dp_get_dsc_sink_cap(intel_dp);
+               intel_dp_get_dsc_sink_cap(intel_dp->dpcd[DP_DPCD_REV],
+                                         intel_dp);
 
        intel_dp_configure_mst(intel_dp);
 
-- 
2.39.2

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