On Fri, May 16, 2025 at 2:01 AM Danilo Krummrich <d...@kernel.org> wrote: > > On Thu, May 15, 2025 at 02:57:46PM -0700, Rob Clark wrote: > > On Thu, May 15, 2025 at 10:55 AM Danilo Krummrich <d...@kernel.org> wrote: > > > Anyways, I don't agree with that. Even if you can tweak your driver to > > > not run > > > into trouble with this, we can't introduce a mode that violates GOUVM's > > > internal > > > lifetimes and subsequently fix it up with WARN_ON() or BUG_ON(). > > > > > > I still don't see a real technical reason why msm can't be reworked to > > > follow > > > those lifetime rules. > > > > The basic issue is that (a) it would be really awkward to have two > > side-by-side VM/VMA management/tracking systems. But in legacy mode, > > we have the opposite direction of reference holding. (But at the same > > time, don't need/use most of the features of gpuvm.) > > Ok, let's try to move this forward; I see three options (in order of > descending > preference): > > 1) Rework the legacy code to properly work with GPUVM. > 2) Don't use GPUVM for the legacy mode. > . > . > . > 3) Get an ACK from Dave / Sima to implement those workarounds for MSM in > GPUVM. > > If you go for 3), the code introduced by those two patches should be guarded > with a flag that makes it very clear that this is a workaround specifically > for MSM legacy mode and does not give any guarantees in terms of correctness > regarding lifetimes etc., e.g. DRM_GPUVM_MSM_LEGACY_QUIRK.
I'm not even sure how #2 would work, other than just copy/pasta all of drm_gpuvm into msm, which doesn't really seem great. As for #1, even if I could get it to work, it would still be a lot more mmu map/unmap (like on every pageflip, vs the current state that the vma is kept around until the object is freed). For the non-VM_BIND world, there are advantages to the BO holding the ref to the VMA, rather than the other way around. Even at just a modest single layer 1080p the map takes ~.2ms and unmap ~.3ms (plus the unmap costs a tlbinv). So from that standpoint, #3 is the superior option. BR, -R
