Re: [Intel-gfx] [PATCH 17/27] drm/i915/guc: Flush G2H work queue during reset

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Aug 20, 2021 at 05:25:41PM -0700, Daniele Ceraolo Spurio wrote:
> 
> 
> On 8/18/2021 11:16 PM, Matthew Brost wrote:
> > It isn't safe to scrub for missing G2H or continue with the reset until
> > all G2H processing is complete. Flush the G2H work queue during reset to
> > ensure it is done running.
> 
> Might be worth moving this patch closer to "drm/i915/guc: Process all G2H
> message at once in work queue".
> 

Sure.

> > Fixes: eb5e7da736f3 ("drm/i915/guc: Reset implementation for new GuC interface")
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >   .../gpu/drm/i915/gt/uc/intel_guc_submission.c  | 18 ++----------------
> >   1 file changed, 2 insertions(+), 16 deletions(-)
> > 
> > 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 4cf5a565f08e..9a53bae367b1 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -714,8 +714,6 @@ static void guc_flush_submissions(struct intel_guc *guc)
> >   void intel_guc_submission_reset_prepare(struct intel_guc *guc)
> >   {
> > -	int i;
> > -
> >   	if (unlikely(!guc_submission_initialized(guc))) {
> >   		/* Reset called during driver load? GuC not yet initialised! */
> >   		return;
> > @@ -731,20 +729,8 @@ void intel_guc_submission_reset_prepare(struct intel_guc *guc)
> >   	guc_flush_submissions(guc);
> > -	/*
> > -	 * Handle any outstanding G2Hs before reset. Call IRQ handler directly
> > -	 * each pass as interrupt have been disabled. We always scrub for
> > -	 * outstanding G2H as it is possible for outstanding_submission_g2h to
> > -	 * be incremented after the context state update.
> > -	 */
> > -	for (i = 0; i < 4 && atomic_read(&guc->outstanding_submission_g2h); ++i) {
> > -		intel_guc_to_host_event_handler(guc);
> > -#define wait_for_reset(guc, wait_var) \
> > -		intel_guc_wait_for_pending_msg(guc, wait_var, false, (HZ / 20))
> > -		do {
> > -			wait_for_reset(guc, &guc->outstanding_submission_g2h);
> > -		} while (!list_empty(&guc->ct.requests.incoming));
> > -	}
> > +	flush_work(&guc->ct.requests.worker);
> > +
> 
> We're now not waiting in the requests anymore, just ensuring that the
> processing of the ones we already received is done. Is this intended? We do
> still handle the remaining oustanding submission in the scrub so it's
> functionally correct, but the commit message doesn't state the change in
> waiting behavior, so wanted to double check it was planned.
> 

Yes, it is planned as scrub code should be able to cope with any missing
G2H. Will update the commit message to reflect that.

Matt

> Daniele
> 
> >   	scrub_guc_desc_for_outstanding_g2h(guc);
> >   }
>