[PATCH 1/2] drm: Fix vblank refcount during modeset

[Yunxiang Li]

drm_crtc_vblank_off increments the refcount to prevent vblank from
getting enabled during modeset, but this causes the refcount elsewhere
to be off if they call drm_vblank_get without checking the return and
do a drm_vblank_put later. This can be reproduced by toggling vrr mode
on amdgpu.

Since drm_crtc_vblank_on later re-enables vblank if the refcount is not
zero, letting drm_vblank_get succeed during modeset should fix the behavior.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/1380
Signed-off-by: Yunxiang Li <Yunxiang.Li at amd.com>
---
 drivers/gpu/drm/drm_vblank.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 2ff31717a3de..159d13b5d97b 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1174,7 +1174,7 @@ int drm_vblank_get(struct drm_device *dev, unsigned int pipe)
 	if (atomic_add_return(1, &vblank->refcount) == 1) {
 		ret = drm_vblank_enable(dev, pipe);
 	} else {
-		if (!vblank->enabled) {
+		if (!vblank->enabled && !vblank->inmodeset) {
 			atomic_dec(&vblank->refcount);
 			ret = -EINVAL;
 		}
-- 
2.37.1