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. */ _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
