Re: [PATCH 2/2] drm/i915: Ignore long hpds on eDP ports

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Oct 17, 2014 at 11:49:54AM +0300, Jani Nikula wrote:
> On Thu, 16 Oct 2014, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Turning vdd on/off can generate a long hpd pulse on eDP ports. In order
> > to handle hpd we would need to turn on vdd to perform aux transfers.
> > This would lead to an endless cycle of
> > "vdd off -> long hpd -> vdd on -> detect -> vdd off -> ..."
> >
> > So ignore long hpd pulses on eDP ports. eDP panels should be physically
> > tied to the machine anyway so they should not actually disappear and
> > thus don't need long hpd handling. Short hpds are still needed for link
> > re-train and whatnot so we can't just turn off the hpd interrupt
> > entirely for eDP ports. Perhaps we could turn it off whenever the panel
> > is disabled, but just ignoring the long hpd seems sufficient.
> 
> Did you test this with my short vs. long hpd fix applied?

Yes. Well, with my own version of it :)

Now someone should go and implement HPD support for port A.

> 
> In any case, makes sense,
> 
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
> 
> 
> 
> 
> 
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index f07f02c..4455009 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -4611,6 +4611,18 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
> >  	if (intel_dig_port->base.type != INTEL_OUTPUT_EDP)
> >  		intel_dig_port->base.type = INTEL_OUTPUT_DISPLAYPORT;
> >  
> > +	if (long_hpd && intel_dig_port->base.type == INTEL_OUTPUT_EDP) {
> > +		/*
> > +		 * vdd off can generate a long pulse on eDP which
> > +		 * would require vdd on to handle it, and thus we
> > +		 * would end up in an endless cycle of
> > +		 * "vdd off -> long hpd -> vdd on -> detect -> vdd off -> ..."
> > +		 */
> > +		DRM_DEBUG_KMS("ignoring long hpd on eDP port %c\n",
> > +			      port_name(intel_dig_port->port));
> > +		return false;
> > +	}
> > +
> >  	DRM_DEBUG_KMS("got hpd irq on port %c - %s\n",
> >  		      port_name(intel_dig_port->port),
> >  		      long_hpd ? "long" : "short");
> > -- 
> > 2.0.4
> >
> > _______________________________________________
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> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center

-- 
Ville Syrjälä
Intel OTC