[PATCH 1/8] drm/xe: Move explicit CT lock in TLB invalidation sequence

[Matthew Brost]

On Thu, Aug 07, 2025 at 11:10:38AM -0600, Summers, Stuart wrote:
> Mi Matt,
> 
> Any thoughts here?
> 

A lock to protect the seqno assignment and calling xe_guc_ct_send or in
the final result a backend op is needed. From seqno assignment, issue
needs to be atomic or issues could get reordered breaking how we signal
fences. ofc we could fix that part a I think a mutex here is easiest way
to go.

Matt 

> Thanks,
> Stuart
> 
> On Wed, 2025-08-06 at 22:23 +0000, stuartsummers wrote:
> > We already have a lock tracking the fences/sequence numbers
> > here (pending_lock). And the GuC CT code already has an
> > implicit version of this lock in the ct_send routine.
> > Prepare the way for future optimizations in TLB invalidation
> > flow by moving the mutex lock down into the GuC CT send
> > routine rather than in the upper TLB invalidation layer.
> > 
> > Signed-off-by: stuartsummers <stuart.summers at intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c | 8 ++------
> >  1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> > b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> > index 02f0bb92d6e0..230f30161395 100644
> > --- a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> > +++ b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
> > @@ -158,7 +158,6 @@ void xe_gt_tlb_invalidation_reset(struct xe_gt
> > *gt)
> >          * appear.
> >          */
> >  
> > -       mutex_lock(&gt->uc.guc.ct.lock);
> >         spin_lock_irq(&gt->tlb_invalidation.pending_lock);
> >         cancel_delayed_work(&gt->tlb_invalidation.fence_tdr);
> >         /*
> > @@ -178,7 +177,6 @@ void xe_gt_tlb_invalidation_reset(struct xe_gt
> > *gt)
> >                                  &gt-
> > >tlb_invalidation.pending_fences, link)
> >                 invalidation_fence_signal(gt_to_xe(gt), fence);
> >         spin_unlock_irq(&gt->tlb_invalidation.pending_lock);
> > -       mutex_unlock(&gt->uc.guc.ct.lock);
> >  }
> >  
> >  static bool tlb_invalidation_seqno_past(struct xe_gt *gt, int seqno)
> > @@ -211,13 +209,12 @@ static int send_tlb_invalidation(struct xe_guc
> > *guc,
> >          * need to be updated.
> >          */
> >  
> > -       mutex_lock(&guc->ct.lock);
> >         seqno = gt->tlb_invalidation.seqno;
> >         fence->seqno = seqno;
> >         trace_xe_gt_tlb_invalidation_fence_send(xe, fence);
> >         action[1] = seqno;
> > -       ret = xe_guc_ct_send_locked(&guc->ct, action, len,
> > -                                   G2H_LEN_DW_TLB_INVALIDATE, 1);
> > +       ret = xe_guc_ct_send(&guc->ct, action, len,
> > +                            G2H_LEN_DW_TLB_INVALIDATE, 1);
> >         if (!ret) {
> >                 spin_lock_irq(&gt->tlb_invalidation.pending_lock);
> >                 /*
> > @@ -248,7 +245,6 @@ static int send_tlb_invalidation(struct xe_guc
> > *guc,
> >                 if (!gt->tlb_invalidation.seqno)
> >                         gt->tlb_invalidation.seqno = 1;
> >         }
> > -       mutex_unlock(&guc->ct.lock);
> >         xe_gt_stats_incr(gt, XE_GT_STATS_ID_TLB_INVAL, 1);
> >  
> >         return ret;
>