Re: [PATCH v2 3/5] drm/i915: Introduce DRM_I915_GEM_MMAP_OFFSET

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Bloomfield, Jon (2019-10-07 17:55:16)
> > -----Original Message-----
> > From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Abdiel
> > Janulgue
> > Sent: Monday, October 7, 2019 2:19 AM
> > To: intel-gfx@lists.freedesktop.org
> > Cc: Auld, Matthew <matthew.auld@intel.com>
> > Subject: [Intel-gfx] [PATCH v2 3/5] drm/i915: Introduce
> > DRM_I915_GEM_MMAP_OFFSET
> > 
> > This is really just an alias of mmap_gtt. Add a new CPU mmap
> > implementation that allows multiple fault handlers that depends on
> > the object's backing pages.
> > 
> > Note that we multiplex mmap_gtt and mmap_offset through the same ioctl,
> > and use the zero extending behaviour of drm to differentiate between
> > them, when we inspect the flags.
> > 
> > Signed-off-by: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
> > Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/gem/i915_gem_mman.c      | 36 +++++++++++++++++--
> >  .../gpu/drm/i915/gem/i915_gem_object_types.h  |  3 ++
> >  drivers/gpu/drm/i915/i915_drv.c               |  2 +-
> >  include/uapi/drm/i915_drm.h                   | 28 +++++++++++++++
> >  4 files changed, 66 insertions(+), 3 deletions(-)
> 
> How does the label 'offset' fit into this API if it's really about multiple fault handlers?
> Could do with a much better description here I think. Who would use this, and why, would help a lot.

The ioctl returns the offset into the device fd userpace uses with
mmap(2). Hence DRM_IOCTL_I915_GEM_MMAP_OFFSET.
-Chris
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