On 2016?01?15? 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 at 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 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. :-) -- ?ark Yao
