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@metanate.com
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 effectplane_commit --> |- get_vblank and wait --> |
| <-- handle_vblank, vblank->count + 1cleanup_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. :-)