[PATCH 02/25] dma-fence: prime lockdep annotations

[Jason Gunthorpe]

On Fri, Jul 10, 2020 at 02:48:16PM +0200, Christian König wrote:
> Am 10.07.20 um 14:43 schrieb Jason Gunthorpe:
> > On Thu, Jul 09, 2020 at 10:09:11AM +0200, Daniel Vetter wrote:
> > > Hi Jason,
> > > 
> > > Below the paragraph I've added after our discussions around dma-fences
> > > outside of drivers/gpu. Good enough for an ack on this, or want something
> > > changed?
> > > 
> > > Thanks, Daniel
> > > 
> > > > + * Note that only GPU drivers have a reasonable excuse for both requiring
> > > > + * &mmu_interval_notifier and &shrinker callbacks at the same time as having to
> > > > + * track asynchronous compute work using &dma_fence. No driver outside of
> > > > + * drivers/gpu should ever call dma_fence_wait() in such contexts.
> > I was hoping we'd get to 'no driver outside GPU should even use
> > dma_fence()'
> 
> My last status was that V4L could come use dma_fences as well.

I'm sure lots of places *could* use it, but I think I understood that
it is a bad idea unless you have to fit into the DRM uAPI?

You are better to do something contained in the single driver where
locking can be analyzed.

> I'm not 100% sure, but wouldn't MMU notifier + dma_fence be a valid use case
> for things like custom FPGA interfaces as well?

I don't think we should expand the list of drivers that use this
technique. 

Drivers that can't suspend should pin memory, not use blocked
notifiers to created pinned memory.

Jason