drm/i915/dp: Extract drm_dp_read_mst_cap()

Just a tiny drive-by cleanup, we can consolidate i915's code for
checking for MST support into a helper to be shared across drivers.

v5:
* Drop !!()
* Move drm_dp_has_mst() out of header
* Change name from drm_dp_has_mst() to drm_dp_read_mst_cap()

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Sean Paul <sean@poorly.run>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200826182456.322681-10-lyude@redhat.com

1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index b23cb2fec3f3..61755c26fac0 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3487,6 +3487,28 @@ static int drm_dp_get_vc_payload_bw(u8 dp_link_bw, u8  dp_link_count)
 }
 
 /**
+ * drm_dp_read_mst_cap() - check whether or not a sink supports MST
+ * @aux: The DP AUX channel to use
+ * @dpcd: A cached copy of the DPCD capabilities for this sink
+ *
+ * Returns: %True if the sink supports MST, %false otherwise
+ */
+bool drm_dp_read_mst_cap(struct drm_dp_aux *aux,
+			 const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	u8 mstm_cap;
+
+	if (dpcd[DP_DPCD_REV] < DP_DPCD_REV_12)
+		return false;
+
+	if (drm_dp_dpcd_readb(aux, DP_MSTM_CAP, &mstm_cap) != 1)
+		return false;
+
+	return mstm_cap & DP_MST_CAP;
+}
+EXPORT_SYMBOL(drm_dp_read_mst_cap);
+
+/**
  * drm_dp_mst_topology_mgr_set_mst() - Set the MST state for a topology manager
  * @mgr: manager to set state for
  * @mst_state: true to enable MST on this connector - false to disable.