On Tue, Jun 25, 2019 at 10:00:42PM +0200, Daniel Vetter wrote: > On Tue, Jun 25, 2019 at 06:59:12PM +0100, Robert Beckett wrote: > > Warn when about to send stale vblank info and add advice to > > documentation on how to avoid. > > > > Signed-off-by: Robert Beckett <[email protected]> > > --- > > drivers/gpu/drm/drm_vblank.c | 17 +++++++++++++++++ > > 1 file changed, 17 insertions(+) > > > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c > > index 603ab105125d..7dabb2bdb733 100644 > > --- a/drivers/gpu/drm/drm_vblank.c > > +++ b/drivers/gpu/drm/drm_vblank.c > > @@ -918,6 +918,19 @@ EXPORT_SYMBOL(drm_crtc_arm_vblank_event); > > * > > * See drm_crtc_arm_vblank_event() for a helper which can be used in > > certain > > * situation, especially to send out events for atomic commit operations. > > + * > > + * Care should be taken to avoid stale timestamps. If: > > + * - your driver has vblank support (i.e. dev->num_crtcs > 0) > > + * - the vblank irq is off (i.e. no one called drm_crtc_vblank_get) > > drm_crtc_vblank_get() so it becomes a neat hyperlink. > > > + * - from the vblank code's pov the pipe is still running (i.e. not > > + * in-between a drm_crtc_vblank_off()/on() pair) > > Not sure the above will lead to great markup, maybe spell out the > drm_crtc_vblank_on() and maybe make it a bit clearer like "i.e. not after > the call to drm_crtc_vblank_off() but before the next call to > drm_crtc_vblank_on()" so it's clear which said of this pair we're talking > about. > > > + * If all of these conditions hold then drm_crtc_send_vblank_event is > > style nit: the enumeration is one sentence (and and oxford comman missing > but whatever), but you don't continue it here. Also, does the enumeration > look pretty in the htmldocs output? > > > + * going to give you a garbage timestamp and and sequence number (the last > > + * recorded before the irq was disabled). If you call > > drm_crtc_vblank_get/put > > + * around it, or after vblank_off, then either of those will have rolled > > things > > + * forward for you. > > Again pls fix the markup so all the function reference stick out and work.
One more style nit: s/you/drivers/, so maybe: "Drivers must either hold a vblank reference acquired through drm_crtc_vblank_get() or the vblank must have been shut off by calling drm_crtc_vblank_off()." Those functions then have in turn links and hints what you also need to do, like not forget to call drm_crtc_vblank_put(). > > > + * So, drivers should call drm_crtc_vblank_off() before this function in > > their > > + * crtc atomic_disable handlers. > > Imo this sentence here is needed but a bit confusing, and we have it > documented already in the atomic_disable hook. > > Other option would be to list all the places where a driver might want to > call this and how they could get it wrong, which imo doesn't make sense. > > With the nits addressed: > > Reviewed-by: Daniel Vetter <[email protected]> > > > */ > > void drm_crtc_send_vblank_event(struct drm_crtc *crtc, > > struct drm_pending_vblank_event *e) > > @@ -925,8 +938,12 @@ void drm_crtc_send_vblank_event(struct drm_crtc *crtc, > > struct drm_device *dev = crtc->dev; > > u64 seq; > > unsigned int pipe = drm_crtc_index(crtc); > > + struct drm_vblank_crtc *vblank = &dev->vblank[pipe]; > > ktime_t now; > > > > + WARN_ONCE(dev->num_crtcs > 0 && !vblank->enabled && !vblank->inmodeset, > > + "sending stale vblank info\n"); > > + > > if (dev->num_crtcs > 0) { > > seq = drm_vblank_count_and_time(dev, pipe, &now); > > } else { > > -- > > 2.18.0 > > > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
