drm/xe: Move LRC seqno to system memory to avoid slow dGPU reads

The LRC seqno is read by the CPU in the fence signaling path. On dGPU
that read can turn into a PCIe transaction when the seqno lives in the
main LRC BO, making the hot-path poll/peek much more expensive.

Allocate a small dedicated seqno BO in system memory and map the seqno
and start_seqno fields from there instead. The GPU still updates the
values, but CPU reads stay in cached system memory and avoid PCIe read
latency.

Update the LRC map/address helpers to accept a BO expression and use the
new lrc->seqno_bo for seqno mappings. Unpin/unmap seqno_bo during
teardown.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20260218043319.809548-4-matthew.brost@intel.com

0 files changed, 0 insertions, 0 deletions