Am 22.07.2014 17:17, schrieb Daniel Vetter: > On Tue, Jul 22, 2014 at 3:45 PM, Christian K?nig > <deathsimple at vodafone.de> wrote: >>> Would that be something you can agree to? >> >> No, the whole enable_signaling stuff should go away. No callback from the >> driver into the fence code, only the other way around. >> >> fence->signaled as well as fence->wait should become mandatory and only >> called from process context without holding any locks, neither atomic nor >> any mutex/semaphore (rcu might be ok). > So for the enable_signaling, that's optional already. It's only for > drivers that don't want to keep interrupts enabled all the time. You > can opt out of that easily. > > Wrt holding no locks at all while calling into any fence functions, > that's just not going to work out. The point here is to make different > drivers work together and we can rework all the ttm and i915 code to > work locklessly in all cases where they need to wait for someone to > complete rendering. Or at least I don't think that's feasible. So if > you insist that no one might call into radeon code then we simply need > to exclude radeon from participating in any shared fencing. But that's > a bit pointless. > >>> Like I've said I think restricting the insanity other people are willing >>> to live with just because you don't like it isn't right. But it is >>> certainly right for you to insist on not being forced into any such >>> design. I think the above would achieve this. >> >> I don't think so. If it's just me I would say that I'm just to cautious and >> the idea is still save to apply to the whole kernel. >> >> But since Dave, Jerome and Ben seems to have similar concerns I think we >> need to agree to a minimum and save interface for all drivers. > Well I haven't yet seen a proposal that actually works.
How about this: Drivers exporting fences need to provide a fence->signaled and a fence->wait function, everything else like fence->enable_signaling or calling fence_signaled() from the driver is optional. Drivers wanting to use exported fences don't call fence->signaled or fence->wait in atomic or interrupt context, and not with holding any global locking primitives (like mmap_sem etc...). Holding locking primitives local to the driver is ok, as long as they don't conflict with anything possible used by their own fence implementation. Christian. > From an intel > pov I don't care that much since we don't care about desktop prime, so > if radeon/nouveau don't want to do that, meh. Imo the design as-is is > fairly sound, and as simple as it can get given the requirements. I > haven't heard an argument convincing me otherwise, so I guess we > won't have prime support on linux that actually works, ever. > -Daniel