Hi,
On Fri, 21 May 2021 at 10:10, Daniel Vetter daniel.vetter@ffwll.ch 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