[PATCH v2 0/2] HID: logitech-dj: Restore device configuration after reset-resume

[Mark Pariente]

When a Unifying receiver is reset on resume, for example because a USB
KVM switch moved it to another host while the system was suspended,
devices that reconnected in the meantime lose their configuration. The
most visible case is HID++ hi-res scrolling, which leaves the wheel
about 15x slower. Patch 2 has the receiver re-announce its connected
devices on reset-resume so that hidpp reconfigures them.

Sashiko pointed out that on Unifying receivers the re-announce can also
hit slots without a known device, and that HID++ connect notifications
then add those devices with an incomplete report descriptor. That can
already happen today, e.g. when Solaar sends the same request on
startup, so patch 1 fixes it separately: on Unifying receivers, unknown
slots are enumerated through DJ notifications instead.

Changes in v2:
- New patch 1/2: don't add devices from HID++ connect notifications on
  Unifying receivers (reported by Sashiko).
- Patch 2/2: code unchanged; the commit message notes the dependency
  on 1/2.
- v1: https://lore.kernel.org/linux-input/20261018224627.60328-1-markpariente@xxxxxxxxx/

Testing:
- Both patches applied to the v7.2 driver and loaded as an out-of-tree
  module on Fedora's 7.2.11 kernel, with an MX Master 3 on a Unifying
  receiver (046d:c52b) behind a USB KVM switch. Devices enumerate
  normally, and hi-res scrolling is restored after the reset-resume
  reproducer described in patch 2.
- The unknown-slot case fixed by patch 1 could not be reproduced here,
  because this KVM switch fully disconnects the receiver, so it was
  verified by code inspection only.
- Lightspeed, Nano and 27 MHz receivers were not tested; patch 1 does
  not change their behaviour, and patch 2 sends them the request
  logi_dj_recv_query_paired_devices() already uses for them.
- The investigation, patches and changelogs were drafted with an LLM
  coding assistant, then reviewed and tested by me.

Mark Pariente (2):
  HID: logitech-dj: Don't add Unifying devices from HID++ notifications
  HID: logitech-dj: Re-announce connected devices on reset-resume

 drivers/hid/hid-logitech-dj.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)


base-commit: ae6927c533a4454570950125ca8ba909c45f20f9
-- 
2.56.0