[PATCH 2/2] drm/i915/guc: Look for a guilty context when an engine reset fails

[Umesh Nerlige Ramappa]

On Tue, Nov 29, 2022 at 01:12:53PM -0800, John.C.Harrison at Intel.com wrote:
>From: John Harrison <John.C.Harrison at Intel.com>
>
>Engine resets are supposed to never happen. But in the case when one
>does (due to unknwon reasons that normally come down to a missing
>w/a), it is useful to get as much information out of the system as
>possible. Given that the GuC effectively dies on such a situation, it
>is not possible to get a guilty context notification back. So do a
>manual search instead. Given that GuC is dead, this is safe because
>GuC won't be changing the engine state asynchronously.
>
>Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
>---
> drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>index 0a42f1807f52c..c82730804a1c4 100644
>--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>@@ -4751,11 +4751,24 @@ static void reset_fail_worker_func(struct work_struct *w)
> 	guc->submission_state.reset_fail_mask = 0;
> 	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>
>-	if (likely(reset_fail_mask))
>+	if (likely(reset_fail_mask)) {
>+		struct intel_engine_cs *engine;
>+		enum intel_engine_id id;
>+
>+		/*
>+		 * GuC is toast at this point - it dead loops after sending the failed
>+		 * reset notification. So need to manually determine the guilty context.
>+		 * Note that it should be safe/reliable to do this here because the GuC
>+		 * is toast and will not be scheduling behind the KMD's back.
>+		 */

Is that defined by the kmd-GuC interface that following a failed reset notification, GuC 
will always dead-loop OR not schedule anything (even on other engines) until KMD takes 
some action? What action should KMD take?

Regards,
Umesh

>+		for_each_engine_masked(engine, gt, reset_fail_mask, id)
>+			intel_guc_find_hung_context(engine);
>+
> 		intel_gt_handle_error(gt, reset_fail_mask,
> 				      I915_ERROR_CAPTURE,
> 				      "GuC failed to reset engine mask=0x%x\n",
> 				      reset_fail_mask);
>+	}
> }
>
> int intel_guc_engine_failure_process_msg(struct intel_guc *guc,
>-- 
>2.37.3
>