drm/i915/dp: Factor out intel_dp_read_dprx_caps()

Factor out a function to read the sink's DPRX capabilities used by a
follow-up patch enabling the DP tunnel BW allocation mode.
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240220211841.448846-10-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -162,6 +162,28 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEI
 	return lttpr_count;
 }
 
+int intel_dp_read_dprx_caps(struct intel_dp *intel_dp, u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+
+	if (intel_dp_is_edp(intel_dp))
+		return 0;
+
+	/*
+	 * Detecting LTTPRs must be avoided on platforms with an AUX timeout
+	 * period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1).
+	 */
+	if (DISPLAY_VER(i915) >= 10 && !IS_GEMINILAKE(i915))
+		if (drm_dp_dpcd_probe(&intel_dp->aux,
+				      DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV))
+			return -EIO;
+
+	if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
+		return -EIO;
+
+	return 0;
+}
+
 /**
  * intel_dp_init_lttpr_and_dprx_caps - detect LTTPR and DPRX caps, init the LTTPR link training mode
  * @intel_dp: Intel DP struct
@@ -192,12 +214,10 @@ int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp)
 	if (!intel_dp_is_edp(intel_dp) &&
 	    (DISPLAY_VER(i915) >= 10 && !IS_GEMINILAKE(i915))) {
 		u8 dpcd[DP_RECEIVER_CAP_SIZE];
+		int err = intel_dp_read_dprx_caps(intel_dp, dpcd);
 
-		if (drm_dp_dpcd_probe(&intel_dp->aux, DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV))
-			return -EIO;
-
-		if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
-			return -EIO;
+		if (err != 0)
+			return err;
 
 		lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd);
 	}

drivers/gpu/drm/i915/display/intel_dp_link_training.h

@@ -11,6 +11,7 @@
 struct intel_crtc_state;
 struct intel_dp;
 
+int intel_dp_read_dprx_caps(struct intel_dp *intel_dp, u8 dpcd[DP_RECEIVER_CAP_SIZE]);
 int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp);
 
 void intel_dp_get_adjust_train(struct intel_dp *intel_dp,