Il 22/08/23 15:26, Jason-JH.Lin ha scritto:
Add spinlock protection to avoid race condition on vblank event
between mtk_drm_crtc_atomic_begin() and mtk_drm_finish_page_flip().
Hello Jason,
Can you please provide more information about this race condition?
(check below)
Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@xxxxxxxxxxxx>
---
drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
index d40142842f85..128a672fe3c9 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
@@ -746,6 +746,9 @@ static void mtk_drm_crtc_atomic_begin(struct drm_crtc *crtc,
crtc);
struct mtk_crtc_state *mtk_crtc_state = to_mtk_crtc_state(crtc_state);
struct mtk_drm_crtc *mtk_crtc = to_mtk_crtc(crtc);
+ unsigned long flags;
+
+ spin_lock_irqsave(&crtc->dev->event_lock, flags);
if (mtk_crtc->event && mtk_crtc_state->base.event)
DRM_ERROR("new event while there is still a pending event\n");
@@ -756,6 +759,8 @@ static void mtk_drm_crtc_atomic_begin(struct drm_crtc *crtc,
...because my suspect is that what creates the race condition in this function is
the unlocked *assignment* to mtk_crtc->event, not the rest.
If I'm right, you don't need to unconditionally spinlock at the beginning of this
function hence ever-so-slightly improving performance compared to this version.
Can you please try this one and check if this *also* solves the issue?
if (mtk_crtc_state->base.event) {
mtk_crtc_state->base.event->pipe = drm_crtc_index(crtc);
WARN_ON(drm_crtc_vblank_get(crtc) != 0);
spin_lock_irqsave(&crtc->dev->event_lock, flags);
mtk_crtc->event = mtk_crtc_state->base.event;
spin_lock_irqrestore(&crtc->dev->event_lock, flags);
mtk_crtc_state->base.event = NULL;
}
P.S.: I'd try that myself, but I can't seem to reproduce the issue.
Regards,
Angelo
