drm/xe/guc/ct: Flush g2h worker in case of g2h response timeout

In case if g2h worker doesn't get opportunity to within specified
timeout delay then flush the g2h worker explicitly.

v2:
- Describe change in the comment and add TODO (Matt B/John H)
- Add xe_gt_warn on fence done after G2H flush (John H)
v3:
- Updated the comment with root cause
- Clean up xe_gt_warn message (John H)

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/issues/1620
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/issues/2902
Signed-off-by: Badal Nilawar <[e-mail]>
Cc: Matthew Brost <[e-mail]>
Cc: Matthew Auld <[e-mail]>
Cc: John Harrison <[e-mail]>
Cc: Himal Prasad Ghimiray <[e-mail]>
Reviewed-by: Himal Prasad Ghimiray <[e-mail]>
Acked-by: Matthew Brost <[e-mail]>
Signed-off-by: Matthew Brost <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
(cherry picked from commit e5152723380404acb8175e0777b1cea57f319a01)
Signed-off-by: Lucas De Marchi <[e-mail]>

drivers/gpu/drm/xe/xe_guc_ct.c

···
 	ret = wait_event_timeout(ct->g2h_fence_wq, g2h_fence.done, HZ);
 
 	/*
+	 * Occasionally it is seen that the G2H worker starts running after a delay of more than
+	 * a second even after being queued and activated by the Linux workqueue subsystem. This
+	 * leads to G2H timeout error. The root cause of issue lies with scheduling latency of
+	 * Lunarlake Hybrid CPU. Issue dissappears if we disable Lunarlake atom cores from BIOS
+	 * and this is beyond xe kmd.
+	 *
+	 * TODO: Drop this change once workqueue scheduling delay issue is fixed on LNL Hybrid CPU.
+	 */
+	if (!ret) {
+		flush_work(&ct->g2h_worker);
+		if (g2h_fence.done) {
+			xe_gt_warn(gt, "G2H fence %u, action %04x, done\n",
+				   g2h_fence.seqno, action[0]);
+			ret = 1;
+		}
+	}
+
+	/*
 	 * Ensure we serialize with completion side to prevent UAF with fence going out of scope on
 	 * the stack, since we have no clue if it will fire after the timeout before we can erase
 	 * from the xa. Also we have some dependent loads and stores below for which we need the