drm/mst: Refactor the flow for payload allocation/removement

[Why]
Today, the allocation/deallocation steps and status is a bit unclear.

For instance, payload->vc_start_slot = -1 stands for "the failure of
updating DPCD payload ID table" and can also represent as "payload is not
allocated yet". These two cases should be handled differently and hence
better to distinguish them for better understanding.

[How]
Define enumeration - ALLOCATION_LOCAL, ALLOCATION_DFP and ALLOCATION_REMOTE
to distinguish different allocation status. Adjust the code to handle
different status accordingly for better understanding the sequence of
payload allocation and payload removement.

For payload creation, the procedure should look like this:
DRM part 1:
* step 1 - update sw mst mgr variables to add a new payload
* step 2 - add payload at immediate DFP DPCD payload table

Driver:
* Add new payload in HW and sync up with DFP by sending ACT

DRM Part 2:
* Send ALLOCATE_PAYLOAD sideband message to allocate bandwidth along the
  virtual channel.

And as for payload removement, the procedure should look like this:
DRM part 1:
* step 1 - Send ALLOCATE_PAYLOAD sideband message to release bandwidth
           along the virtual channel
* step 2 - Clear payload allocation at immediate DFP DPCD payload table

Driver:
* Remove the payload in HW and sync up with DFP by sending ACT

DRM part 2:
* update sw mst mgr variables to remove the payload

Note that it's fine to fail when communicate with the branch device
connected at immediate downstrean-facing port, but updating variables of
SW mst mgr and HW configuration should be conducted anyway. That's because
it's under commit_tail and we need to complete the HW programming.

Changes since v1:
* Remove the set but not use variable 'old_payload' in function
  'nv50_msto_prepare'. Catched by kernel test robot <lkp@intel.com>

Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230807025639.1612361-3-Wayne.Lin@amd.com

1 files changed, 18 insertions, 5 deletions

diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
index ed5c9660563c..4429d3b1745b 100644
--- a/include/drm/display/drm_dp_mst_helper.h
+++ b/include/drm/display/drm_dp_mst_helper.h
@@ -46,6 +46,13 @@ struct drm_dp_mst_topology_ref_history {
 };
 #endif /* IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS) */
 
+enum drm_dp_mst_payload_allocation {
+	DRM_DP_MST_PAYLOAD_ALLOCATION_NONE,
+	DRM_DP_MST_PAYLOAD_ALLOCATION_LOCAL,
+	DRM_DP_MST_PAYLOAD_ALLOCATION_DFP,
+	DRM_DP_MST_PAYLOAD_ALLOCATION_REMOTE,
+};
+
 struct drm_dp_mst_branch;
 
 /**
@@ -537,7 +544,7 @@ struct drm_dp_mst_atomic_payload {
 	 *   drm_dp_mst_atomic_wait_for_dependencies() has been called, which will ensure the
 	 *   previous MST states payload start slots have been copied over to the new state. Note
 	 *   that a new start slot won't be assigned/removed from this payload until
-	 *   drm_dp_add_payload_part1()/drm_dp_remove_payload() have been called.
+	 *   drm_dp_add_payload_part1()/drm_dp_remove_payload_part2() have been called.
 	 * * Acquire the MST modesetting lock, and then wait for any pending MST-related commits to
 	 *   get committed to hardware by calling drm_crtc_commit_wait() on each of the
 	 *   &drm_crtc_commit structs in &drm_dp_mst_topology_state.commit_deps.
@@ -564,6 +571,9 @@ struct drm_dp_mst_atomic_payload {
 	/** @dsc_enabled: Whether or not this payload has DSC enabled */
 	bool dsc_enabled : 1;
 
+	/** @payload_allocation_status: The allocation status of this payload */
+	enum drm_dp_mst_payload_allocation payload_allocation_status;
+
 	/** @next: The list node for this payload */
 	struct list_head next;
 };
@@ -842,10 +852,13 @@ int drm_dp_add_payload_part1(struct drm_dp_mst_topology_mgr *mgr,
 int drm_dp_add_payload_part2(struct drm_dp_mst_topology_mgr *mgr,
 			     struct drm_atomic_state *state,
 			     struct drm_dp_mst_atomic_payload *payload);
-void drm_dp_remove_payload(struct drm_dp_mst_topology_mgr *mgr,
-			   struct drm_dp_mst_topology_state *mst_state,
-			   const struct drm_dp_mst_atomic_payload *old_payload,
-			   struct drm_dp_mst_atomic_payload *new_payload);
+void drm_dp_remove_payload_part1(struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_mst_topology_state *mst_state,
+				 struct drm_dp_mst_atomic_payload *payload);
+void drm_dp_remove_payload_part2(struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_mst_topology_state *mst_state,
+				 const struct drm_dp_mst_atomic_payload *old_payload,
+				 struct drm_dp_mst_atomic_payload *new_payload);
 
 int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr);