[PATCH] drm/xe: Explicitly cast to u64 to avoid overflow

[Zbigniew Kempczyński]

On Fri, Jun 14, 2024 at 06:20:39AM +0000, Matthew Brost wrote:
> On Fri, Jun 14, 2024 at 07:15:56AM +0200, Zbigniew Kempczyński wrote:
> > Without casting whole expression will be calculated on u32 what
> > means adding U32_MAX effectively decreases the result by one due to
> > overflow. Fix this and use explicit cast to u64.
> > 
> > Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> > Cc: Matthew Brost <matthew.brost at intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_guc_submit.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c
> > index 74552391dc5a..347773f003f3 100644
> > --- a/drivers/gpu/drm/xe/xe_guc_submit.c
> > +++ b/drivers/gpu/drm/xe/xe_guc_submit.c
> > @@ -967,7 +967,7 @@ static bool check_timeout(struct xe_exec_queue *q, struct xe_sched_job *job)
> >  	xe_gt_assert(gt, timeout_ms < 100 * MSEC_PER_SEC);
> >  
> >  	if (ctx_timestamp < ctx_job_timestamp)
> > -		diff = ctx_timestamp + U32_MAX - ctx_job_timestamp;
> > +		diff = (u64) ctx_timestamp + U32_MAX - ctx_job_timestamp;
> 
> I think the existing logic is correct, it dealing with the wrap of a u32
> counter. There be a better way to code this though but this patch
> doesn't look correct to me.

You're right, effect is same regardless u32/u64. Please ignore this patch.

--
Zbigniew

> 
> Matt
> 
> >  	else
> >  		diff = ctx_timestamp - ctx_job_timestamp;
> >  
> > -- 
> > 2.34.1
> >