Re: [PATCH 13/17] drm/i915: Update intel_dp_hpd_pulse() to check link status for non-MST operation

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Dec 17, 2014 at 03:57:21PM -0200, Paulo Zanoni wrote:
> 2014-12-10 21:53 GMT-02:00 Todd Previte <tprevite@gmail.com>:
> > Moves the non-MST case out of the if-statement and places it at the beginning
> > of the function to handle HPD events for SST mode. The reasoning behind this
> > is to accommodate link status checks for compliance testing. Some test devices
> > use long pulses to perform test requests so link status must be checked
> > regardless of the pulse width for the SST operational mode.
> 
> Can you please elaborate a little more on what do you see on these
> devices? The test spec is very clear about short vs long HPD pulses,
> so it's hard to believe a test device would get this wrong. We have
> some registers on the PCH that allow us to redefine short vs long
> durations. Have you tried to play with them?
> 
> More below:
> 
> >
> > This patch replaces [PATCH 10/10] drm/i915: Fix intel_dp_hot_plug() in the
> > previous compliance testing patch sequence. Review feedback on that patch
> > indicated that updating intel_dp_hot_plug() was not the correct place for
> > the test handler.
> >
> > Signed-off-by: Todd Previte <tprevite@gmail.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 22 ++++++++++++----------
> >  1 file changed, 12 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 4a55ca6..73014d8 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -4613,6 +4613,18 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
> >         power_domain = intel_display_port_power_domain(intel_encoder);
> >         intel_display_power_get(dev_priv, power_domain);
> >
> > +       if (!intel_dp->is_mst) {
> > +               /*
> > +                *  Pulse width doesn't matter for SST mode
> > +                *  Handle the HPD event now
> > +               */
> > +               drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > +               intel_dp_check_link_status(intel_dp);
> 
> The very first thing intel_dp_check_link_status() does is to return in
> case "connector->base.status != connected". If we're getting a long
> HPD, it doesn't seem make sense to check this field because the status
> might be changing due to the long HPD.

I don't think we can unconditionally run SST hpd logic before we've
correctly handled mst mode. It likely screws up the accounting.
> 
> > +               drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > +               ret = false;
> > +               goto put_power;
> > +       }
> > +
> >         if (long_hpd) {
> >
> >                 if (HAS_PCH_SPLIT(dev)) {
> > @@ -4637,16 +4649,6 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
> >                         if (intel_dp_check_mst_status(intel_dp) == -EINVAL)
> >                                 goto mst_fail;
> >                 }
> > -
> > -               if (!intel_dp->is_mst) {
> > -                       /*
> > -                        * we'll check the link status via the normal hot plug path later -
> > -                        * but for short hpds we should check it now
> > -                        */

Just aside: The above comment is outdated and can be remove. This is now
the only place where we handle link retraining. The function could be made
static and dropped from headers, too.
-Daniel

> > -                       drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > -                       intel_dp_check_link_status(intel_dp);
> > -                       drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > -               }
> >         }
> >         ret = false;
> >         goto put_power;
> > --
> > 1.9.1
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> 
> 
> -- 
> Paulo Zanoni
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

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