[PATCH v3 0/2] Input: discard pre-registration events and test state seeding

[Karlos Abel <kabel@voidship.net>]

This series prevents input handlers from receiving buffered initialization
events after device registration. On a ThinkPad T14 Gen 6, a later LED
update flushed a stale SW_RFKILL_ALL event seeded by thinkpad_acpi.
The fix drops the pending events and their timestamp before handlers
attach, while retaining the seeded switch and absolute-axis state.

Patch 1 contains the runtime fix. Patch 2 adds KUnit coverage for
registration with and without event-buffer resizing. The test uses a
virtual SW_DOCK device and performs no real radio operations.

Tested on mainline 3857c2fe5449541e24afc5efdb0f81a8a8f9a3a0:
 - V3 with both patches: all six input-core KUnit tests pass under UML,
   with CONFIG_PROVE_LOCKING and CONFIG_DEBUG_SPINLOCK enabled. No
   compiler warnings or lockdep diagnostics were reported.
 - The unchanged tests previously failed against the unmodified input
   core: four passed and two failed. The non-resizing case replayed one
   stale switch event; both cases retained the initialization timestamp.

Earlier versions using a scoped spinlock guard were also tested with
QEMU/KVM on Arch 7.2.7 and on the ThinkPad. V3 uses the same underlying
lock/unlock operations but has not been rerun on physical hardware.

AI assistance: OpenAI Codex assisted source analysis, the fix, regression
tests and this text. The submitter performed the physical hardware
comparisons.

Previous version:
 Message-ID: <20261010191033.23577-1-kabel@voidship.net>
Review addressed:
 Message-ID: <sashiko-outbox-166847@kernel.org>

Changes in v3:
 - Use an explicit spin_lock_irq()/spin_unlock_irq() pair instead of
   adding scoped cleanup to the goto-based registration path.
 - Include the spinlock declarations directly.
 - Patch 2 is unchanged from v2.

Changes in v2:
 - Check absinfo allocation before test event seeding.
 - Unregister the test handler before unregistering its device.

Karlos Abel (2):
  Input: discard pre-registration events before attaching handlers
  Input: test state seeding across device registration

 drivers/input/input.c            |   7 ++
 drivers/input/tests/input_test.c | 171 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 178 insertions(+)

base-commit: 3857c2fe5449541e24afc5efdb0f81a8a8f9a3a0