[PATCH] drm/amd/display: fix NULL checks for adev->dm.dc in amdgpu_dm_fini()

[Nikita Zhandarovich]

Since 'adev->dm.dc' in amdgpu_dm_fini() might turn out to be NULL
before the call to dc_enable_dmub_notifications(), check
beforehand to ensure there will not be a possible NULL-ptr-deref
there.

Also, since commit 1e88eb1b2c25 ("drm/amd/display: Drop
CONFIG_DRM_AMD_DC_HDCP") there are two separate checks for NULL in
'adev->dm.dc' before dc_deinit_callbacks() and dc_dmub_srv_destroy().
Clean up by combining them all under one 'if'.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 81927e2808be ("drm/amd/display: Support for DMUB AUX")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c    | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 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 d292f290cd6e..46ac3e6f42bb 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -1938,17 +1938,15 @@ static void amdgpu_dm_fini(struct amdgpu_device *adev)
 		adev->dm.hdcp_workqueue = NULL;
 	}
 
-	if (adev->dm.dc)
+	if (adev->dm.dc) {
 		dc_deinit_callbacks(adev->dm.dc);
-
-	if (adev->dm.dc)
 		dc_dmub_srv_destroy(&adev->dm.dc->ctx->dmub_srv);
-
-	if (dc_enable_dmub_notifications(adev->dm.dc)) {
-		kfree(adev->dm.dmub_notify);
-		adev->dm.dmub_notify = NULL;
-		destroy_workqueue(adev->dm.delayed_hpd_wq);
-		adev->dm.delayed_hpd_wq = NULL;
+		if (dc_enable_dmub_notifications(adev->dm.dc)) {
+			kfree(adev->dm.dmub_notify);
+			adev->dm.dmub_notify = NULL;
+			destroy_workqueue(adev->dm.delayed_hpd_wq);
+			adev->dm.delayed_hpd_wq = NULL;
+		}
 	}
 
 	if (adev->dm.dmub_bo)
-- 
2.25.1