op 22-07-14 16:39, Christian König schreef: > Am 22.07.2014 16:27, schrieb Maarten Lankhorst: >> op 22-07-14 16:24, Christian König schreef: >>>> No, you really shouldn't be doing much in the check anyway, it's meant to be a lightweight check. If you're not ready yet because of a lockup simply return not signaled yet. >>> It's not only the lockup case from radeon I have in mind here. For userspace queues it might be necessary to call copy_from_user to figure out if a fence is signaled or not. >>> >>> Returning false all the time is probably not a good idea either. >> Having userspace implement a fence sounds like an awful idea, why would you want to do that? > > Marketing moves in mysterious ways. Don't ask me, but that the direction it currently moves with userspace queues and IOMMU etc... > >> A fence could be exported to userspace, but that would only mean it can wait for it to be signaled with an interface like poll.. > > Yeah agree totally, but the point for the fence interface is that I can't predict what's necessary to check if a fence is signaled or not on future hardware. > > For the currently available radeon hardware I can say that reading a value from a kernel page is pretty much all you need. But for older hardware that was reading from a register which might become very tricky if the hardware is power off or currently inside a reset cycle. > > Because off this I would avoid any such interface if it's not absolutely required by some use case, and currently I don't see this requirement because the functionality you want to archive could be implemented without this. Oh? I've already done that in radeon_fence, there is no way enable_signaling will fiddle with hardware registers during a reset cycle. I've also made sure that __radeon_fence_is_signaled grabs exclusive_lock in read mode before touching any hw state. Older hardware also doesn't implement optimus, so I think power off is not much of a worry for them, if you could point me at the checking done for that I could make sure that this is the case. ~Maarten _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
