[PATCH v4 1/7] drm/panthor: Add support for atomic page table updates

[Steven Price]

On 21/08/2025 12:51, Boris Brezillon wrote:
> On Wed, 16 Jul 2025 16:43:24 +0100
> Steven Price <steven.price at arm.com> wrote:
[...]
>> Although in general I'm a bit wary of relying on the whole lock region
>> feature - previous GPUs have an errata. But maybe I'm being over
>> cautious there.
> 
> We're heavily relying on it already to allow updates of the VM while
> the GPU is executing stuff. If that's problematic on v10+, I'd rather
> know early :D.

I think I'm just scarred by my experiences over a decade ago... ;)

I'm not aware of any issues with the modern[1] GPUs. The issue used to
be that the lock region could get accidentally unlocked by a cache flush
from another source - specifically the cache flush on job start flag.

It's also not a major issue if you keep the page tables consistent, the
lock region in theory allows a region to be in an inconsistent state -
but generally there's no need for that. AFAIK we mostly keep the tables
consistent anyway.

Thanks,
Steve

[1] Which in this context means well over a decade - it's somewhat scary
how long I've been doing this!

> Regards,
> 
> Boris