drm/i915: Reorder hpd init vs. display resume

drm/i915: Reorder hpd init vs. display resume

Currently we call .hpd_irq_setup() directly just before display
resume, and follow it with another call via intel_hpd_init()
just afterwards. Assuming the hpd pins are marked as enabled
during the open-coded call these two things do exactly the
same thing (ie. enable HPD interrupts). Which even makes sense
since we definitely need working HPD interrupts for MST sideband
during the display resume.

So let's nuke the open-coded call and move the intel_hpd_init()
call earlier. However we need to leave the poll_init_work stuff
behind after the display resume as that will trigger display
detection while we're resuming. We don't want that trampling over
the display resume process. To make this a bit more symmetric
we turn this into a intel_hpd_poll_{enable,disable}() pair.
So we end up with the following transformation:
intel_hpd_poll_init() -> intel_hpd_poll_enable()
lone intel_hpd_init() -> intel_hpd_init()+intel_hpd_poll_disable()
.hpd_irq_setup()+resume+intel_hpd_init() -> intel_hpd_init()+resume+intel_hpd_poll_disable()

If we really would like to prevent all *long* HPD processing during
display resume we'd need some kind of software mechanism to simply
ignore all long HPDs. Currently we appear to have that just for
fbdev via ifbdev->hpd_suspended. Since we aren't exploding left and
right all the time I guess that's mostly sufficient.

For a bit of history on this, we first got a mechanism to block
hotplug processing during suspend in commit 15239099d7a7 ("drm/i915:
enable irqs earlier when resuming") on account of moving the irq enable
earlier. This then got removed in commit 50c3dc970a09 ("drm/fb-helper:
Fix hpd vs. initial config races") because the fdev initial config
got pushed to a later point. The second ad-hoc hpd_irq_setup() for
resume was added in commit 0e32b39ceed6 ("drm/i915: add DP 1.2 MST
support (v0.7)") to be able to do MST sideband during the resume.
And finally we got a partial resurrection of the hpd blocking
mechanism in commit e8a8fedd57fd ("drm/i915: Block fbdev HPD
processing during suspend"), but this time it only prevent fbdev
from handling hpd while resuming.

v2: Leave the poll_init_work behind
v3: Remove the extra intel_hpd_poll_disable() from display reset (Lyude)
    Add the missing intel_hpd_poll_disable() to display init (Imre)

Cc: Lyude Paul <lyude@redhat.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201013181137.30560-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>