drm/xe/lrc: fix spurious warning when reading context timestamp

Fixes the following warning that fires during timeout handling for a
context running on the USM-reserved copy engine:

  xe 0000:03:00.0: [drm] Tile0: GT0: Unexpected engine class:instance 3:8 for utilization
  WARNING: at engine_id_to_hwe+0x88/0xc0 [xe]
    xe_lrc_context_timestamp+0x61/0xb0 [xe]
    guc_exec_queue_timedout_job+0x713/0x1020 [xe]

class:instance 3:8 is XE_ENGINE_CLASS_COPY on the highest BCS instance,
which xe_hw_engine.c reserves for USM (gt->usm.reserved_bcs_instance) and
on which the migrate engine runs kernel contexts. When such a context's
utilization is read - e.g. from the TDR path - engine_id_to_hwe()
rejected it because xe_hw_engine_is_reserved() is true, firing WARN_ONCE
and returning NULL, which made the timestamp read silently fall back to
stale data.

The reserved-engine guard was added defensively with the original WA BB
utilization support and simply overlooked that the migrate engine is a
valid, present engine whose CTX_TIMESTAMP can legitimately be read.

Allow the USM-reserved copy engine specifically (xe_gt_is_usm_hwe()),
while still rejecting the other reserved cases (GSCCS / XE_ENGINE_CLASS_
OTHER and ccs_mode-disabled compute engines), which would indeed be
unexpected on this path. The dynamic engine resolution via the ENGINE_ID
stashed in the PPHWSP by the WA BB is kept intact, so utilization for
load-balanced/virtual exec queues still resolves the engine the context
is actually running on.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Assisted-by: GitHub-Copilot:claude-sonnet-4.6
Assisted-by: GitHub-Copilot:claude-opus-4.8
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patch.msgid.link/20260610152548.404575-4-rodrigo.vivi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

0 files changed, 0 insertions, 0 deletions