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authorJohn Keeping <john@metanate.com>2016-01-19 10:47:00 +0000
committerMark Yao <mark.yao@rock-chips.com>2016-01-20 08:56:06 +0800
commitc9ad1d9946e849ac3d8821d91e136d7fd728dec5 (patch)
tree55bdf59e04f94c426173e8fea79674c6c10596de /drivers/gpu
parentf2227f469782e55765deacb8ebcc7ec05fe04013 (diff)
drm/rockchip: explain why we can't wait_for_vblanks
Signed-off-by: John Keeping <john@metanate.com>
Diffstat (limited to 'drivers/gpu')
-rw-r--r--drivers/gpu/drm/rockchip/rockchip_drm_fb.c15
1 files changed, 15 insertions, 0 deletions
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
index 87c77c4b5e50..3b8f652698f8 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
@@ -176,6 +176,21 @@ 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)
{