Re: [PATCH v3 3/4] drm/vblank: estimate vblank while disabling vblank if interrupt disabled

Daniel Vetter
2019-06-26T14:30:31Z

On Wed, Jun 26, 2019 at 04:27:32PM +0300, Ville Syrjälä wrote:
> On Tue, Jun 25, 2019 at 06:59:14PM +0100, Robert Beckett wrote:
> > If interrupts are disabled (e.g. via vblank_disable_fn) and we come to
> > disable vblank, update the vblank count to best guess as to what it
> > would be had the interrupts remained enabled, and update the timesamp to
> > now.
> >
> > This avoids a stale vblank event being sent while disabling crtcs during
> > atomic modeset.
> >
> > Fixes: 68036b08b91bc ("drm/vblank: Do not update vblank count if interrupts
> > are already disabled.")
>
> I don't understand that commit. drm_vblank_off() should be called
> when the power is still present, so it looks to me like that
> commit is actually wrong. So I think we may want to just revert
> it and figure out what the actual bug was.

Hm yeah we might need a power domain get/put around our
drm_crtc_vblank_off() call to make sure it dtrt. Revert sounds like a good
idea instead of adding more kludges ... a-b: me on the revert, even though
I did ack the original patch too.
-Daniel

>
> >
> > Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
> > ---
> > drivers/gpu/drm/drm_vblank.c | 16 +++++++++++++++-
> > 1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > index 7dabb2bdb733..db68b8cbf797 100644
> > --- a/drivers/gpu/drm/drm_vblank.c
> > +++ b/drivers/gpu/drm/drm_vblank.c
> > @@ -375,9 +375,23 @@ void drm_vblank_disable_and_save(struct drm_device *dev, unsigned int pipe)
> > * interrupts were enabled. This avoids calling the ->disable_vblank()
> > * operation in atomic context with the hardware potentially runtime
> > * suspended.
> > + * If interrupts are disabled (e.g. via blank_disable_fn) then make
> > + * best guess as to what it would be now and make sure we have an up
> > + * to date timestamp.
> > */
> > - if (!vblank->enabled)
> > + if (!vblank->enabled) {
> > + ktime_t now = ktime_get();
> > + u32 diff = 0;
> > + if (vblank->framedur_ns) {
> > + u64 diff_ns = ktime_to_ns(ktime_sub(now, vblank->time));
> > + diff = DIV_ROUND_CLOSEST_ULL(diff_ns,
> > + vblank->framedur_ns);
> > + }
> > +
> > + store_vblank(dev, pipe, diff, now, vblank->count);
> > +
> > goto out;
> > + }
> >
> > /*
> > * Update the count and timestamp to maintain the
> > --
> > 2.18.0
> >
> > _______________________________________________
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> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Ville Syrjälä
> Intel
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> dri-devel@lists.freedesktop.org
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--
Daniel Vetter
Software Engineer, Intel Corporation