Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns

From	Keith Packard <keithp@keithp.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns
Date	2017-07-06 17:20 +0200
Message-ID	<u0gJr-6NU-3@gated-at.bofh.it> (permalink)
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Michel Dänzer <michel@daenzer.net> writes:

> BTW, this got me thinking that we should probably treat
> _DRM_VBLANK_NEXTONMISS the same way, i.e. clear the flag after updating
> vblwait->request.sequence. Otherwise there could theoretically (though
> unlikely) be an infinite loop:

I was thinking that we should just re-compute the target sequence from
scratch and not modify the request at all. But, now I see your point --
if the wait is interrupted long after it starts, then we don't want to
change the target number.

I wonder if anyone actually waits for vblank anymore, or if everyone
just uses the event interface...

> ioctl with _DRM_VBLANK_NEXTONMISS, target missed => wait for next vblank
> wait interrupted by signal
> lather, rinse, repeat

Yeah, sounds like a latent bug.

Ok, to retract my last email, I'll go ahead and fix things up so that
the request sequence gets set to the correct absolute value and that any
flags which modify it get cleared.

> I'd advise against adding a "next on miss" flag for the new ioctl until
> there is specific demand for that.

Thanks for your advice :-)

-- 
-keith

Thread

[PATCH 0/3] drm: Add CRTC-id based ioctls for vblank query/event Keith Packard <keithp@keithp.com> - 2017-07-06 00:20 +0200
  [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns Keith Packard <keithp@keithp.com> - 2017-07-06 00:20 +0200
    Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank  time precision to ns Daniel Vetter <daniel@ffwll.ch> - 2017-07-06 09:30 +0200
      Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns Keith Packard <keithp@keithp.com> - 2017-07-06 17:10 +0200
        Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank  time precision to ns Daniel Vetter <daniel@ffwll.ch> - 2017-07-07 14:20 +0200
    Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank  time precision to ns Michel Dänzer <michel@daenzer.net> - 2017-07-06 09:50 +0200
      Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank  time precision to ns Michel Dänzer <michel@daenzer.net> - 2017-07-06 10:10 +0200
        Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns Keith Packard <keithp@keithp.com> - 2017-07-06 17:20 +0200
      Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns Keith Packard <keithp@keithp.com> - 2017-07-06 17:10 +0200
        Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank  time precision to ns Michel Dänzer <michel@daenzer.net> - 2017-07-07 03:40 +0200
          Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank  time precision to ns Michel Dänzer <michel@daenzer.net> - 2017-07-07 04:10 +0200
  [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls Keith Packard <keithp@keithp.com> - 2017-07-06 00:20 +0200
    Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE  ioctls Daniel Vetter <daniel@ffwll.ch> - 2017-07-06 10:00 +0200
      Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE  ioctls Ville Syrjälä <ville.syrjala@linux.intel.com> - 2017-07-06 12:20 +0200
        Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls Daniel Vetter <daniel@ffwll.ch> - 2017-07-06 13:10 +0200
          Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE  ioctls Ville Syrjälä <ville.syrjala@linux.intel.com> - 2017-07-06 16:10 +0200
            Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls Keith Packard <keithp@keithp.com> - 2017-07-06 18:30 +0200
              Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE  ioctls Ville Syrjälä <ville.syrjala@linux.intel.com> - 2017-07-06 20:10 +0200
                Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls Keith Packard <keithp@keithp.com> - 2017-07-06 20:30 +0200
                Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE  ioctls Ville Syrjälä <ville.syrjala@linux.intel.com> - 2017-07-06 21:00 +0200
                Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls Keith Packard <keithp@keithp.com> - 2017-07-06 21:50 +0200
      Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls Keith Packard <keithp@keithp.com> - 2017-07-06 18:30 +0200
        Re: [PATCH 3/3] drm: Add CRTC_GET_SEQUENCE and CRTC_QUEUE_SEQUENCE ioctls Daniel Vetter <daniel@ffwll.ch> - 2017-07-06 23:50 +0200
  [PATCH 2/3] drm: Reorganize drm_pending_event to support future event types Keith Packard <keithp@keithp.com> - 2017-07-06 00:20 +0200
    Re: [PATCH 2/3] drm: Reorganize drm_pending_event to support future  event types Daniel Vetter <daniel@ffwll.ch> - 2017-07-06 09:40 +0200
      Re: [PATCH 2/3] drm: Reorganize drm_pending_event to support future event types Keith Packard <keithp@keithp.com> - 2017-07-06 17:40 +0200
        Re: [PATCH 2/3] drm: Reorganize drm_pending_event to support future  event types Daniel Vetter <daniel@ffwll.ch> - 2017-07-07 14:10 +0200

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