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Subject: [PATCH v2 1/3] drm/dp_mst: add passthrough_aux to struct drm_dp_mst_port
Date:   Fri, 5 Aug 2022 17:13:03 -0400
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Currently, there is no way to identify if DSC pass-through can be
enabled and what aux DSC pass-through requests ought to be sent to. So,
add a variable to struct drm_dp_mst_port that keeps track of the
aforementioned information.

Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
---
v2: define DP_DSC_PASSTHROUGH_IS_SUPPORTED
---
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 4 +++-
 include/drm/display/drm_dp.h                  | 1 +
 include/drm/display/drm_dp_mst_helper.h       | 3 +++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 67b3b9697da7..71915afd9892 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -5921,8 +5921,10 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
 		/* Enpoint decompression with DP-to-DP peer device */
 		if ((endpoint_dsc & DP_DSC_DECOMPRESSION_IS_SUPPORTED) &&
 		    (endpoint_fec & DP_FEC_CAPABLE) &&
-		    (upstream_dsc & 0x2) /* DSC passthrough */)
+		    (upstream_dsc & DP_DSC_PASSTHROUGH_IS_SUPPORTED)) {
+			port->passthrough_aux = &immediate_upstream_port->aux;
 			return &port->aux;
+		}
 
 		/* Virtual DPCD decompression with DP-to-DP peer device */
 		return &immediate_upstream_port->aux;
diff --git a/include/drm/display/drm_dp.h b/include/drm/display/drm_dp.h
index 9e3aff7e68bb..4d0abe4c7ea9 100644
--- a/include/drm/display/drm_dp.h
+++ b/include/drm/display/drm_dp.h
@@ -239,6 +239,7 @@
 
 #define DP_DSC_SUPPORT                      0x060   /* DP 1.4 */
 # define DP_DSC_DECOMPRESSION_IS_SUPPORTED  (1 << 0)
+# define DP_DSC_PASSTHROUGH_IS_SUPPORTED    (1 << 1)
 
 #define DP_DSC_REV                          0x061
 # define DP_DSC_MAJOR_MASK                  (0xf << 0)
diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
index 10adec068b7f..4a39c95f8afd 100644
--- a/include/drm/display/drm_dp_mst_helper.h
+++ b/include/drm/display/drm_dp_mst_helper.h
@@ -86,6 +86,8 @@ struct drm_dp_vcpi {
  * @next: link to next port on this branch device
  * @aux: i2c aux transport to talk to device connected to this port, protected
  * by &drm_dp_mst_topology_mgr.base.lock.
+ * @passthrough_aux: parent aux to which DSC pass-through requests should be
+ * sent, only set if DSC pass-through is possible.
  * @parent: branch device parent of this port
  * @vcpi: Virtual Channel Payload info for this port.
  * @connector: DRM connector this port is connected to. Protected by
@@ -140,6 +142,7 @@ struct drm_dp_mst_port {
 	 */
 	struct drm_dp_mst_branch *mstb;
 	struct drm_dp_aux aux; /* i2c bus for this port? */
+	struct drm_dp_aux *passthrough_aux;
 	struct drm_dp_mst_branch *parent;
 
 	struct drm_dp_vcpi vcpi;
-- 
2.37.1