Signed-off-by: John Keeping <john@xxxxxxxxxxxx>
---
v2:
- Add more detail of the particular race that could happen if we used
drm_atomic_helper_wait_for_vblanks().
drivers/gpu/drm/rockchip/rockchip_drm_fb.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
index 679d23a..cf0b7bd 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
@@ -177,6 +177,21 @@ static void rockchip_crtc_wait_for_update(struct drm_crtc *crtc)
crtc_funcs->wait_for_update(crtc);
}
+/*
+ * We can't use drm_atomic_helper_wait_for_vblanks() because rk3288 and rk3066
+ * have hardware counters for neither vblanks nor scanlines, which results in
+ * a race where:
+ * | <-- HW vsync irq and reg take effect
+ * plane_commit --> |
+ * get_vblank and wait --> |
+ * | <-- handle_vblank, vblank->count + 1
+ * cleanup_fb --> |
+ * iommu crash --> |
+ * | <-- HW vsync irq and reg take effect
+ *
+ * This function is equivalent but uses rockchip_crtc_wait_for_update() instead
+ * of waiting for vblank_count to change.
+ */
static void
rockchip_atomic_wait_for_complete(struct drm_device *dev, struct drm_atomic_state *old_state)
{
--
2.7.0.226.gfe986fe
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