On 2016年01月15日 00:26, John Keeping wrote:
On Thu, 14 Jan 2016 15:57:05 +0100, Thierry Reding wrote:
On Thu, Jan 14, 2016 at 02:39:42PM +0000, John Keeping wrote:
Signed-off-by: John Keeping <john@xxxxxxxxxxxx>
---
drivers/gpu/drm/rockchip/rockchip_drm_fb.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
index 679d23a..b267ce4 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
@@ -177,6 +177,12 @@ 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. This function is
+ * equivalent but uses rockchip_crtc_wait_for_update() instead of waiting for
+ * vblank_count to change.
+ */
This is kind of misleading. From reading earlier parts of the thread the
reason why drm_atomic_helper_wait_for_vblanks() won't work is because it
has a potential race condition that can't be detected unless you also
have a vblank counter. However, the above comment makes it work like
drm_atomic_helper_wait_for_vblanks() doesn't work in the absence of a
vblank counter, which isn't quite true.
How about something like this (using the sequence from Mark's message):
/*
* 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.
*/
Looks good for me, but maybe Thierry has some more advices. :-)
--
Ｍark Yao
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