Quoting Zbigniew Kempczyński (2021-03-11 11:44:32)
On Wed, Mar 10, 2021 at 03:50:07PM -0600, Jason Ekstrand wrote:
The Vulkan driver in Mesa for Intel hardware never uses relocations if it's running on a version of i915 that supports at least softpin which all versions of i915 supporting Gen12 do. On the OpenGL side, Gen12+ is only supported by iris which never uses relocations. The older i965 driver in Mesa does use relocations but it only supports Intel hardware through Gen11 and has been deprecated for all hardware Gen9+. The compute driver also never uses relocations. This only leaves the media driver which is supposed to be switching to softpin going forward. Making softpin a requirement for all future hardware seems reasonable.
Rejecting relocations starting with Gen12 has the benefit that we don't have to bother supporting it on platforms with local memory. Given how much CPU touching of memory is required for relocations, not having to do so on platforms where not all memory is directly CPU-accessible carries significant advantages.
v2 (Jason Ekstrand):
- Allow TGL-LP platforms as they've already shipped
v3 (Jason Ekstrand):
- WARN_ON platforms with LMEM support in case the check is wrong
I was asked to review of this patch. It works along with expected IGT check https://patchwork.freedesktop.org/patch/423361/?series=82954&rev=25
Before I'll give you r-b - isn't i915_gem_execbuffer2_ioctl() better place to do for loop just after copy_from_user() and check relocation_count? We have an access to exec2_list there, we know the gen so we're able to say relocations are not supported immediate, without entering i915_gem_do_execbuffer().
There's a NORELOC flag you can enforce as mandatory. That's trivial for userspace to set, really makes sure they are aware of the change afoot, and i915_gem_ceck_execbuffer() will perform the validation upfront with the other flag checks. -Chris