[Query] amdgpu_dm_crtc_mem_type_changed always compares the same plane state

[ALOK TIWARI]

Hi,

The function amdgpu_dm_crtc_mem_type_changed() in 
amdgpu/display/dm_helpers.c appears to have a logical issue:

new_plane_state = drm_atomic_get_plane_state(state, plane);
old_plane_state = drm_atomic_get_plane_state(state, plane);

Both new_plane_state and old_plane_state are obtained from 
drm_atomic_get_plane_state(state, plane),
which means they will always point to the same plane state. As a result, 
the subsequent check:

if (old_plane_state->fb && new_plane_state->fb &&
    get_mem_type(old_plane_state->fb) != get_mem_type(new_plane_state->fb))
    return true;
        
such case it will never detect a change in memory type, because 
old_plane_state and new_plane_state are identical.

Proposed fix: use drm_atomic_get_old_plane_state() to retrieve the 
previous plane state:

---
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 8e1622bf7a42..74f4f7e7b119 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -11968,7 +11968,7 @@ static bool 
amdgpu_dm_crtc_mem_type_changed(struct drm_device *dev,

        drm_for_each_plane_mask(plane, dev, crtc_state->plane_mask) {
                new_plane_state = drm_atomic_get_plane_state(state, plane);
-               old_plane_state = drm_atomic_get_plane_state(state, plane);
+               old_plane_state = drm_atomic_get_old_plane_state(state, 
plane); //<<

                if (IS_ERR(new_plane_state) || IS_ERR(old_plane_state)) {
                        drm_err(dev, "Failed to get plane state for 
plane %s\n", plane->name);


Thanks,
Alok