Re: [PATCH v2] drm/i915/lspcon: Enable AUX interrupts for resume time initialization

[Imre Deak <imre.deak@intel.com>]

On ti, 2016-11-29 at 23:00 +0200, Ville Syrjälä wrote:
> [...]
> > > > > There is a slight concern on g4x/vlv/chv that an AUX interrupts
> > > > > would
> > > > > trigger the hpd irq handler, which doesn't realize it's supposed
> > > > > to
> > > > > ignore the actual hpd bits in PORT_HOTPLUG_STAT. So any aux
> > > > > before we
> > > > > enable hpd processing for real could do something bad. So I guess
> > > > > we
> > > > > should add some kind of software tracking for that stuff like we
> > > > > have
> > > > > for PIPESTAT.
> > > > 
> > > > Didn't think about that, but BSpec tells me those are masked by the
> > > > HPD
> > > > IRQ enable bits in PORT_HOTPLUG_EN and those we enable only later.
> > > > Otherwise this would be also a problem during output setup time.
> > > 
> > > Hmm. Are they really masked? I though it's just an IER effectively.
> > 
> > I only tried for real on BXT/SKL where I had to enable the interrupts
> > (in PCH_PORT_HOTPLUG) for HPD sensing. The CHV BSpec suggests the same
> > for the live state bits, but yes it's not clear if the long/short
> > detect bits are completely masked by the enable flags or they are just
> > not propagated if not enabled. Will give it a try tomorrow.
> 
> Hmm. Yeah, we did in fact chat about this. Already forgot. Spec seems to
> suggest you are correct. But checking on actual hw is always a good
> idea.

Checked now both on BXT and VLV both the live state and short/long
detect bits in the hotplug_stat reg are masked by the hotplug_en bits.
(And we clear any stale short/long bits during IRQ reset.)

--Imre
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