[PATCH 13/14][SRU][OEM-5.14] drm/amd/display: Don't lock connection_mutex for DMUB HPD

[You-Sheng Yang]

From: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>

BugLink: https://bugs.launchpad.net/bugs/1953008

[Why]
Per DRM spec we only need to hold that lock when touching
connector->state - which we do not do in that handler.

Taking this locking introduces unnecessary dependencies with other
threads which is bad for performance and opens up the potential for
a deadlock since there are multiple locks being held at once.

[How]
Remove the connection_mutex lock/unlock routine and just iterate over
the drm connectors normally. The iter helpers implicitly lock the
connection list so this is safe to do.

DC link access also does not need to be guarded since the link
table is static at creation - we don't dynamically add or remove links,
just streams.

Fixes: e27c41d5b068 ("drm/amd/display: Support for DMUB HPD interrupt handling")

Reviewed-by: Jude Shih <shenshih at amd.com>
Acked-by: Anson Jacob <Anson.Jacob at amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler at amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
(cherry picked from commit d82b3266ef88dc10fe0e7031b2bd8ba7eedb7e59)
Signed-off-by: You-Sheng Yang <vicamo.yang at canonical.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index db310cd62124..00be19bc4cec 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -669,10 +669,7 @@ void dmub_hpd_callback(struct amdgpu_device *adev, struct dmub_notification *not
 		return;
 	}
 
-	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
-
 	link_index = notify->link_index;
-
 	link = adev->dm.dc->links[link_index];
 
 	drm_connector_list_iter_begin(dev, &iter);
@@ -685,7 +682,6 @@ void dmub_hpd_callback(struct amdgpu_device *adev, struct dmub_notification *not
 		}
 	}
 	drm_connector_list_iter_end(&iter);
-	drm_modeset_unlock(&dev->mode_config.connection_mutex);
 
 	if (hpd_aconnector)
 		handle_hpd_irq_helper(hpd_aconnector);
-- 
2.32.0