[Intel-gfx] [RFC PATCH 2/2] drm/i915: Account for platform without mappable aperture when returning size

[Chris Wilson]

Quoting Antonio Argenziano (2019-03-07 22:21:17)
> 
> 
> On 07/03/19 13:59, Chris Wilson wrote:
> > Quoting Antonio Argenziano (2019-03-07 19:11:15)
> >> Some devices will not expose a mappable aperture anymore so we need to
> >> return an appropriate value in that case.
> >>
> >> Signed-off-by: Antonio Argenziano <antonio.argenziano at intel.com>
> >>
> >> Cc: Matthew Auld <matthew.auld at intel.com>
> >> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >> ---
> >>   drivers/gpu/drm/i915/i915_gem.c | 3 ++-
> >>   1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >> index d109f6dbe992..5125a5329100 100644
> >> --- a/drivers/gpu/drm/i915/i915_gem.c
> >> +++ b/drivers/gpu/drm/i915/i915_gem.c
> >> @@ -221,7 +221,8 @@ i915_gem_get_aperture_ioctl(struct drm_device *dev, void *data,
> >>          args->aper_size = ggtt->vm.total;
> >>          args->aper_available_size = args->aper_size - pinned;
> >>   
> >> -       args->mappable_aperture_size = ggtt->mappable_end;
> >> +       args->mappable_aperture_size =
> >> +                       HAS_MAPPABLE_APERTURE(to_i915(dev)) ? ggtt->mappable_end : (__u64)-ENODEV;
> > 
> > Looking above, args->aper_size will also be 0 so that'll be a good clue
> 
> Is it? ggtt should still be there so that shouldn't be zero.

Fair enough. We could lie though. Userspace isn't allowed to directly
access aper after gen7 (full-ppgtt), only via GGTT mmaps. With no more
GGTT mmaps, aper_size is ostensibly meaningless.

However, you never know, so keeping the information we do have and
reporting no mappable HW as ENODEV has a certain charm. Let's see if
anyone else has a better idea.
-Chris