Hi, On Fri, 21 May 2021 at 10:10, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > Currently this has no practial relevance I think because there's not > many who can pull off a setup with panfrost and another gpu in the > same system. But the rules are that if you're setting an exclusive > fence, indicating a gpu write access in the implicit fencing system, > then you need to wait for all fences, not just the previous exclusive > fence. > > panfrost against itself has no problem, because it always sets the > exclusive fence (but that's probably something that will need to be > fixed for vulkan and/or multi-engine gpus, or you'll suffer badly). > Also no problem with that against display. Yeah, the 'second-generation Valhall' GPUs coming later this year / early next year are starting to get pretty weird. Firmware-mediated job scheduling out of multiple queues, userspace having direct access to the queues and can do inter-queue synchronisation (at least I think so), etc. For bonus points, synchronisation is based on $addr = $val to signal and $addr == $val to wait, with a separate fence primitive as well. Obviously Arm should be part of this conversation here, but I guess we'll have to wait for a while yet to see how everything's shaken out with this new gen, and hope that whatever's been designed upstream in the meantime is actually vaguely compatible ... Cheers, Daniel
