Re: [PATCH] drm/i915: Make sure PSR is ready for been re-enabled.

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Sep 24, 2014 at 12:40:20PM -0300, Paulo Zanoni wrote:
> 2014-09-17 14:23 GMT-03:00 Rodrigo Vivi <rodrigo.vivi@intel.com>:
> > Let's make sure PSR is propperly disabled before to re-enabled it.
> >
> > According to Spec, after disabled PSR CTL, the Idle state might occur
> > up to 24ms, that is one full frame time (1/refresh rate),
> > plus SRD exit training time (max of 6ms),
> > plus SRD aux channel handshake (max of 1.5ms).
> >
> > v2: The 24ms above takes in account 16ms for refresh rate on 60Hz mode. However
> > on low frequency modes this can take longer. So let's use 50ms for safeness.
> 
> Well, the patch looks correct, but it doesn't seem to take into
> consideration the fact that we already waited for 100ms before
> triggering psr.work. Also, we do the wait that you added with psr.lock
> locked, so we could be blocking user-space from doing other stuff for
> the whole 50ms, and that's an eternity and a half.
> 
> So maybe we should tune the schedule_delayed_work() call at
> intel_edp_psr_flush() based on the calculation you did above (or just
> keep the 100ms, since it seems to be above the timeout for any modes
> bigger than 11Hz). And then when we're inside the work function, we
> should just I915_READ(EDP_PSR_STATUS_CTL) - instead of doing
> wait_for() -, and in case PSR is not idle yet, there's a huge
> probability that waiting for more 50ms won't really help. We could
> also try to reschedule psr.work to be triggered again in the future in
> case the bits we want are not ready, but by doing this we also risk
> rescheduling psr.work forever.
> 
> More bikeshed on the timeout thing: can't we try discover the exact
> amount of time we need to sleep based on the refresh rate? We could
> try to look at the mode structure...
> 
> tl;dr: if you remove the wait_for() call and keep just the I915_READ,
> I can give a R-B tag, but other patches could be acceptable too.

Hm, I think just moving the wait_for outside of the psr.lock critical
section should be good enough. Only the work item here can enable PSR, so
there's not really a race. And on the disable side we always sync with the
work before shutting down the psr work, so no synchronization issues
either. At worst the dpms off will take a few ms more.

Merged the 3rd patch meanwhile, thanks.
-Daniel

> 
> 
> >
> > So if something went wrong PSR will be disabled until next full
> > enable/disable setup.
> >
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 2f0eee5..2e8c544 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -1885,6 +1885,17 @@ static void intel_edp_psr_do_enable(struct intel_dp *intel_dp)
> >         WARN_ON(dev_priv->psr.active);
> >         lockdep_assert_held(&dev_priv->psr.lock);
> >
> > +       /* We have to make sure PSR is ready for re-enable
> > +        * otherwise it keeps disabled until next full enable/disable cycle.
> > +        * PSR might take some time to get fully disabled
> > +        * and be ready for re-enable.
> > +        */
> > +       if (wait_for((I915_READ(EDP_PSR_STATUS_CTL(dev)) &
> > +                     EDP_PSR_STATUS_STATE_MASK) == 0, 50)) {
> > +               DRM_ERROR("Timed out waiting for PSR Idle for re-enable\n");
> > +               return;
> > +       }
> > +
> >         /* Enable/Re-enable PSR on the host */
> >         intel_edp_psr_enable_source(intel_dp);
> >
> > --
> > 1.9.3
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> 
> 
> -- 
> Paulo Zanoni

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch