[PATCH 6.1.y] drm/amd/display: fix NULL checks for adev->dm.dc in amdgpu_dm_fini()

[jianqi.ren.cn at windriver.com]

From: Nikita Zhandarovich <n.zhandarovich at fintech.ru>

[ Upstream commit 2a3cfb9a24a28da9cc13d2c525a76548865e182c ]

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 at fintech.ru>
Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Jianqi Ren <jianqi.ren.cn at windriver.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 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 8dc0f70df24f..7b4d44dcb343 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -1882,14 +1882,14 @@ static void amdgpu_dm_fini(struct amdgpu_device *adev)
 		dc_deinit_callbacks(adev->dm.dc);
 #endif
 
-	if (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