Re: [PATCH v4 5/7] drm/panfrost: Add a new ioctl to submit batches

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 8 Jul 2021 14:10:45 +0200
Christian König <ckoenig.leichtzumerken@gmail.com> wrote:

> >> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> >> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> >> @@ -254,6 +254,9 @@ static int panfrost_acquire_object_fences(struct panfrost_job *job)
> >>   				return ret;
> >>   		}
> >>   
> >> +		if (job->bo_flags[i] & PANFROST_BO_REF_NO_IMPLICIT_DEP)
> >> +			continue;  
> > This breaks dma_resv rules. I'll send out patch set fixing this pattern in
> > other drivers, I'll ping you on that for what you need to change. Should
> > go out today or so.

I guess you're talking about [1]. TBH, I don't quite see the point of
exposing a 'no-implicit' flag if we end up forcing this implicit dep
anyway, but I'm probably missing something.

> 
> I'm really wondering if the behavior that the exclusive fences replaces 
> all the shared fences was such a good idea.

Is that what's done in [1], or are you talking about a different
patchset/approach?

> 
> It just allows drivers to mess up things in a way which can be easily 
> used to compromise the system.

I must admit I'm a bit lost, so I'm tempted to drop that flag for now
:-).

[1]https://patchwork.freedesktop.org/patch/443711/?series=92334&rev=3