[PATCH v2 8/8] drm/panfrost: Remove unnecessary flushing from tlb_inv_context

[Rob Herring]

On Fri, Aug 23, 2019 at 7:56 AM Robin Murphy <robin.murphy at arm.com> wrote:
>
> On 23/08/2019 03:12, Rob Herring wrote:
> > tlb_inv_context() hook is only called when freeing the page tables. There's
> > no point in flushing only to free the page tables immediately following.
>
> FWIW, in general the point of flushing is *because* we're about to free
> the pagetables - if there's any possibility that the hardware could
> continue to issue translation table walks (speculative or otherwise)
> after those pages have been reused by someone else, TLB badness may ensue.
>
> For panfrost in particular I suspect we can probably get away without
> it, at least for the moment, but it might be worth moving the flush to
> mmu_disable() for complete peace of mind (which kind of preempts the
> sort of thing that per-process AS switching will want anyway).

There's bigger problem that mmu_disable() is still only called for AS0
and only for driver unload. I guess we should fix that and then figure
out where a flush is needed if at all. I would think changing the TTBR
would be enough to quiesce the h/w and TLBs. That seems to be the case
in my testing of switching address spaces.

Rob