drm/amd/display: Fork thread to offload work of hpd_rx_irq

[Why]
Currently, we will try to get dm.dc_lock in handle_hpd_rx_irq() when
link lost happened, which is risky and could cause deadlock.
e.g. If we are under procedure to enable MST streams and then monitor
happens to toggle short hpd to notify link lost, then
handle_hpd_rx_irq() will get blocked due to stream enabling flow has
dc_lock. However, under MST, enabling streams involves communication
with remote sinks which need to use handle_hpd_rx_irq() to handle
sideband messages. Thus, we have deadlock here.

[How]
Target is to have handle_hpd_rx_irq() finished as soon as possilble.
Hence we can react to interrupt quickly. Besides, we should avoid to
grabe dm.dc_lock within handle_hpd_rx_irq() to avoid deadlock situation.

Firstly, revert patches which introduced to use dm.dc_lock in
handle_hpd_rx_irq():

* commit ("drm/amd/display: NULL pointer error during ")

* commit ("drm/amd/display: Only one display lights up while using MST")

* commit ("drm/amd/display: take dc_lock in short pulse handler only")

Instead, create work to handle irq events which needs dm.dc_lock.
Besides:

* Create struct hpd_rx_irq_offload_work_queue for each link to handle
  its short hpd events

* Avoid to handle link lost/ automated test if the link is disconnected

* Defer dc_lock needed works in dc_link_handle_hpd_rx_irq(). This
  function should just handle simple stuff for us (e.g. DPCD R/W).
  However, deferred works should still be handled by the order that
  dc_link_handle_hpd_rx_irq() used to be.

* Change function name dm_handle_hpd_rx_irq() to
  dm_handle_mst_sideband_msg() to be more specific

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 48 insertions, 1 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
index be796c2fed7d..a038c70037b5 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
@@ -172,6 +172,48 @@ struct dal_allocation {
 };
 
 /**
+ * struct hpd_rx_irq_offload_work_queue - Work queue to handle hpd_rx_irq
+ * offload work
+ */
+struct hpd_rx_irq_offload_work_queue {
+	/**
+	 * @wq: workqueue structure to queue offload work.
+	 */
+	struct workqueue_struct *wq;
+	/**
+	 * @offload_lock: To protect fields of offload work queue.
+	 */
+	spinlock_t offload_lock;
+	/**
+	 * @is_handling_link_loss: Used to prevent inserting link loss event when
+	 * we're handling link loss
+	 */
+	bool is_handling_link_loss;
+	/**
+	 * @aconnector: The aconnector that this work queue is attached to
+	 */
+	struct amdgpu_dm_connector *aconnector;
+};
+
+/**
+ * struct hpd_rx_irq_offload_work - hpd_rx_irq offload work structure
+ */
+struct hpd_rx_irq_offload_work {
+	/**
+	 * @work: offload work
+	 */
+	struct work_struct work;
+	/**
+	 * @data: reference irq data which is used while handling offload work
+	 */
+	union hpd_irq_data data;
+	/**
+	 * @offload_wq: offload work queue that this work is queued to
+	 */
+	struct hpd_rx_irq_offload_work_queue *offload_wq;
+};
+
+/**
  * struct amdgpu_display_manager - Central amdgpu display manager device
  *
  * @dc: Display Core control structure
@@ -461,7 +503,12 @@ struct amdgpu_display_manager {
 	 */
 	struct crc_rd_work *crc_rd_wrk;
 #endif
-
+	/**
+	 * @hpd_rx_offload_wq:
+	 *
+	 * Work queue to offload works of hpd_rx_irq
+	 */
+	struct hpd_rx_irq_offload_work_queue *hpd_rx_offload_wq;
 	/**
 	 * @mst_encoders:
 	 *