drm/i915: Fix hpd handling for pins with two encoders

drm/i915: Fix hpd handling for pins with two encoders

In my haste to remove irq_port[] I accidentally changed the
way we deal with hpd pins that are shared by multiple encoders
(DP and HDMI for pre-DDI platforms). Previously we would only
handle such pins via ->hpd_pulse(), but now we queue up the
hotplug work for the HDMI encoder directly. Worse yet, we now
count each hpd twice and this increment the hpd storm count
twice as fast. This can lead to spurious storms being detected.

Go back to the old way of doing things, ie. delegate to
->hpd_pulse() for any pin which has an encoder with that hook
implemented. I don't really like the idea of adding irq_port[]
back so let's loop through the encoders first to check if we
have an encoder with ->hpd_pulse() for the pin, and then go
through all the pins and decided on the correct course of action
based on the earlier findings.

I have occasionally toyed with the idea of unifying the pre-DDI
HDMI and DP encoders into a single encoder as well. Besides the
hotplug processing it would have the other benefit of preventing
userspace from trying to enable both encoders at the same time.
That is simply illegal as they share the same clock/data pins.
We have some testcases that will attempt that and thus fail on
many older machines. But for now let's stick to fixing just the
hotplug code.

Cc: stable@vger.kernel.org # 4.19+
Cc: Lyude Paul <lyude@redhat.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Fixes: b6ca3eee18ba ("drm/i915: Nuke dev_priv->irq_port[]")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181108200424.28371-1-ville.syrjala@linux.intel.com
Reviewed-by: Lyude Paul <lyude@redhat.com>