drm/i915/gt: Increase a time to retry RING_HEAD reset

Issue seen again where engine resets fails because the engine resumes from
an incorrect RING_HEAD. HEAD is still not 0 even after writing into it.
This seems to be timing issue and we experimented different values from 5ms
to 50ms and found out that 50ms works best based on testing.
So, if write doesn't succeed at first then retry again.

v2: add a comment (Andi Shyti)

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12806
Signed-off-by: Nitin Gote <[email protected]>
Reviewed-by: Andi Shyti <[email protected]>
Signed-off-by: Andi Shyti <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: NitinGote

drivers/gpu/drm/i915/gt/intel_ring_submission.c

@@ -230,8 +230,13 @@ static int xcs_resume(struct intel_engine_cs *engine)
 
 	set_pp_dir(engine);
 
-	/* First wake the ring up to an empty/idle ring */
-	for ((kt) = ktime_get() + (2 * NSEC_PER_MSEC);
+	/*
+	 * First wake the ring up to an empty/idle ring.
+	 * Use 50ms of delay to let the engine write successfully
+	 * for all platforms. Experimented with different values and
+	 * determined that 50ms works best based on testing.
+	 */
+	for ((kt) = ktime_get() + (50 * NSEC_PER_MSEC);
 			ktime_before(ktime_get(), (kt)); cpu_relax()) {
 		/*
 		 * In case of resets fails because engine resumes from