[PATCH AUTOSEL 5.15 03/20] drm/amd/display: Avoid MPC infinite loop

[Sasha Levin]

From: Josip Pavic <josip.pa...@amd.com>

[ Upstream commit 8de297dc046c180651c0500f8611663ae1c3828a ]

[why]
In some cases MPC tree bottom pipe ends up point to itself.  This causes
iterating from top to bottom to hang the system in an infinite loop.

[how]
When looping to next MPC bottom pipe, check that the pointer is not same
as current to avoid infinite loop.

Reviewed-by: Josip Pavic <josip.pa...@amd.com>
Reviewed-by: Jun Lei <jun....@amd.com>
Acked-by: Alex Hung <alex.h...@amd.com>
Signed-off-by: Aric Cyr <aric....@amd.com>
Tested-by: Daniel Wheeler <daniel.whee...@amd.com>
Signed-off-by: Alex Deucher <alexander.deuc...@amd.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 drivers/gpu/drm/amd/display/dc/dcn10/dcn10_mpc.c | 6 ++++++
 drivers/gpu/drm/amd/display/dc/dcn20/dcn20_mpc.c | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_mpc.c 
b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_mpc.c
index 11019c2c62cc..8192f1967e92 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_mpc.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_mpc.c
@@ -126,6 +126,12 @@ struct mpcc *mpc1_get_mpcc_for_dpp(struct mpc_tree *tree, 
int dpp_id)
        while (tmp_mpcc != NULL) {
                if (tmp_mpcc->dpp_id == dpp_id)
                        return tmp_mpcc;
+
+               /* avoid circular linked list */
+               ASSERT(tmp_mpcc != tmp_mpcc->mpcc_bot);
+               if (tmp_mpcc == tmp_mpcc->mpcc_bot)
+                       break;
+
                tmp_mpcc = tmp_mpcc->mpcc_bot;
        }
        return NULL;
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_mpc.c 
b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_mpc.c
index 947eb0df3f12..142fc0a3a536 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_mpc.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_mpc.c
@@ -532,6 +532,12 @@ struct mpcc *mpc2_get_mpcc_for_dpp(struct mpc_tree *tree, 
int dpp_id)
        while (tmp_mpcc != NULL) {
                if (tmp_mpcc->dpp_id == 0xf || tmp_mpcc->dpp_id == dpp_id)
                        return tmp_mpcc;
+
+               /* avoid circular linked list */
+               ASSERT(tmp_mpcc != tmp_mpcc->mpcc_bot);
+               if (tmp_mpcc == tmp_mpcc->mpcc_bot)
+                       break;
+
                tmp_mpcc = tmp_mpcc->mpcc_bot;
        }
        return NULL;
-- 
2.35.1