[Intel-gfx] [PATCH] drm/i915/gem: Drop relocation support on all new hardware (v6)

[Jason Ekstrand]

I should probably have said that the reviews are on v5 and it's very
different in v6 so they should probably be considered dropped until
re-confirmed.

On Wed, Mar 17, 2021 at 9:39 AM Jason Ekstrand <jason at jlekstrand.net> 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.
>
> There is one piece of hardware enabled by default in i915: RKL which was
> enabled by e22fa6f0a976 which has not yet landed in drm-next so this
> almost but not really a userspace API change for RKL.  If it becomes a
> problem, we can always add !IS_ROCKETLAKE(eb->i915) to the condition.
>
> Rejecting relocations starting with newer Gen12 platforms 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
>
> v4 (Jason Ekstrand):
>  - Call out Rocket Lake in the commit message
>
> v5 (Jason Ekstrand):
>  - Drop the HAS_LMEM check as it's already covered by the version check
>
> v6 (Jason Ekstrand):
>  - Move the check to eb_validate_vma() with all the other exec_object
>    validation checks.
>
> Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
> Reviewed-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 99772f37bff60..c082fb0bef330 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -483,6 +483,13 @@ eb_validate_vma(struct i915_execbuffer *eb,
>                 struct drm_i915_gem_exec_object2 *entry,
>                 struct i915_vma *vma)
>  {
> +       /* Relocations are disallowed for all platforms after TGL-LP.  This
> +        * also covers all platforms with local memory.
> +        */
> +       if (entry->relocation_count &&
> +           INTEL_GEN(eb->i915) >= 12 && !IS_TIGERLAKE(eb->i915))
> +               return -EINVAL;
> +
>         if (unlikely(entry->flags & eb->invalid_flags))
>                 return -EINVAL;
>
> --
> 2.29.2
>