[PATCH i-g-t 0/7] Validate PM_PME signalling on display hotplug

[Pranay Samala <pranay.samala@intel.com>]

A display hotplug can be signalled as a PCI PME while the graphics device
is runtime suspended in D3hot. That lets the driver leave the
drm_kms_helper connector poll worker disabled across runtime suspend, so
the device stays parked instead of being resumed every ~10s just to probe
connectors.

The property worth validating is therefore not "does a hotplug still
work" - the polling fallback delivers that too, just slowly and at the
cost of the power saving. It is "does the hotplug work while polling
stays off". A test that only toggles HPD and waits for a uevent passes
either way, and would not notice the feature regressing into the
fallback.

So the new subtest runs two phases against the same suspended device:

  Phase 1: hold the device idle in D3hot for 25s and check from PCI
           config space that it never leaves D3hot. This is the power
           saving.
  Phase 2: toggle HPD from D3hot and check that a uevent arrives, that
           the connector status updated, and that
           power/wakeup_active_count incremented - i.e. that the resume
           was signalled by the device and not initiated by the host.

Patches 1-2 add the PCI Power Management capability register layout and
accessors for PME_Support, PME_En, PME_Status and the PowerState field.
PME_Status distinguishes a device that signalled but was never
acknowledged from one that never signalled at all, which makes a failure
report actionable instead of just "no uevent".

Patches 3-5 add the power/wakeup and power/wakeup_active_count
accessors, with patch 3 factoring out the path construction they share.
active_count is used rather than wakeup_count because the latter never
moves for a runtime resume.

Patch 6 adds igt_pm_kms_poll_save(), _set() and _restore(). The two
tests that already open code this are converted in a separate series
that depends on this one, since one of them also has a pre-existing
restore-without-save bug unrelated to PME.

Patch 7 adds the subtest.

Pranay Samala (7):
  lib/igt_pci: Add PCI Power Management capability register layout
  lib/igt_pm: Add PCI PME capability and D state accessors
  lib/igt_pm: Factor out power attribute path construction
  lib/igt_pm: Add power/wakeup accessors
  lib/igt_pm: Add power/wakeup_active_count accessor
  lib/igt_pm: Add drm_kms_helper.poll save/restore helpers
  tests/chamelium/kms_chamelium_hpd: Add HPD from runtime suspended
    D3hot

 lib/igt_pci.h                       |  12 +
 lib/igt_pm.c                        | 457 +++++++++++++++++++++++++++-
 lib/igt_pm.h                        |  12 +
 tests/chamelium/kms_chamelium_hpd.c | 344 +++++++++++++++++++++
 4 files changed, 816 insertions(+), 9 deletions(-)

-- 
2.53.0