drm/dp: Factor out helper to distinguish between branch and sink devices

This check is open-coded in a few places, so it makes sense to simplify
things by having a helper for it similar to the rest of DPCD feature
helpers.

v2: (Jani)
- Move the helper to drm_dp_helper.h.
- Split out this change to a separate patch.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477326811-30431-2-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -1459,8 +1459,7 @@ static void intel_dp_print_hw_revision(struct intel_dp *intel_dp)
 	if ((drm_debug & DRM_UT_KMS) == 0)
 		return;
 
-	if (!(intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
-	      DP_DWN_STRM_PORT_PRESENT))
+	if (!drm_dp_is_branch(intel_dp->dpcd))
 		return;
 
 	len = drm_dp_dpcd_read(&intel_dp->aux, DP_BRANCH_HW_REV, &rev, 1);
@@ -1478,8 +1477,7 @@ static void intel_dp_print_sw_revision(struct intel_dp *intel_dp)
 	if ((drm_debug & DRM_UT_KMS) == 0)
 		return;
 
-	if (!(intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
-	      DP_DWN_STRM_PORT_PRESENT))
+	if (!drm_dp_is_branch(intel_dp->dpcd))
 		return;
 
 	len = drm_dp_dpcd_read(&intel_dp->aux, DP_BRANCH_SW_REV, &rev, 2);
@@ -3615,8 +3613,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 	if (!is_edp(intel_dp) && !intel_dp->sink_count)
 		return false;
 
-	if (!(intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
-	      DP_DWN_STRM_PORT_PRESENT))
+	if (!drm_dp_is_branch(intel_dp->dpcd))
 		return true; /* native DP sink */
 
 	if (intel_dp->dpcd[DP_DPCD_REV] == 0x10)
@@ -4134,7 +4131,7 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 		return connector_status_connected;
 
 	/* if there's no downstream port, we're done */
-	if (!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
+	if (!drm_dp_is_branch(dpcd))
 		return connector_status_connected;
 
 	/* If we're HPD-aware, SINK_COUNT changes dynamically */

include/drm/drm_dp_helper.h

@@ -690,6 +690,12 @@ drm_dp_tps3_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 		dpcd[DP_MAX_LANE_COUNT] & DP_TPS3_SUPPORTED;
 }
 
+static inline bool
+drm_dp_is_branch(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	return dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT;
+}
+
 /*
  * DisplayPort AUX channel
  */