> -Original Message-
> From: dri-devel On Behalf Of
> Thomas Hellström
> Sent: Tuesday, February 22, 2022 2:36 AM
> To: Auld, Matthew ; intel-...@lists.freedesktop.org
> Cc: Daniel Vetter ; dri-de...@lists.freedesktop.org;
> Kenneth Graunke ; Bloomfield, Jon
> ; Justen, Jordan L ;
> mesa-dev@lists.freedesktop.org
> Subject: Re: [PATCH 2/2] drm/doc: add rfc section for small BAR uapi
>
>
> On 2/18/22 12:22, Matthew Auld wrote:
> > Add an entry for the new uapi needed for small BAR on DG2+.
> >
> > Signed-off-by: Matthew Auld
> > Cc: Thomas Hellström
> > Cc: Jon Bloomfield
> > Cc: Daniel Vetter
> > Cc: Jordan Justen
> > Cc: Kenneth Graunke
> > Cc: mesa-dev@lists.freedesktop.org
> > ---
> > Documentation/gpu/rfc/i915_small_bar.h | 153
> +++
> > Documentation/gpu/rfc/i915_small_bar.rst | 40 ++
> > Documentation/gpu/rfc/index.rst | 4 +
> > 3 files changed, 197 insertions(+)
> > create mode 100644 Documentation/gpu/rfc/i915_small_bar.h
> > create mode 100644 Documentation/gpu/rfc/i915_small_bar.rst
> >
> > diff --git a/Documentation/gpu/rfc/i915_small_bar.h
> > b/Documentation/gpu/rfc/i915_small_bar.h
> > new file mode 100644
> > index ..fa65835fd608
> > --- /dev/null
> > +++ b/Documentation/gpu/rfc/i915_small_bar.h
> > @@ -0,0 +1,153 @@
> > +/**
> > + * struct __drm_i915_gem_create_ext - Existing gem_create behaviour,
> > +with added
> > + * extension support using struct i915_user_extension.
> > + *
> > + * Note that in the future we want to have our buffer flags here,
>
> Does this sentence need updating, with the flags member?
>
>
> > at least for
> > + * the stuff that is immutable. Previously we would have two ioctls,
> > +one to
> > + * create the object with gem_create, and another to apply various
> > +parameters,
> > + * however this creates some ambiguity for the params which are
> > +considered
> > + * immutable. Also in general we're phasing out the various SET/GET ioctls.
> > + */
> > +struct __drm_i915_gem_create_ext {
> > + /**
> > +* @size: Requested size for the object.
> > +*
> > +* The (page-aligned) allocated size for the object will be returned.
> > +*
> > +* Note that for some devices we have might have further minimum
> > +* page-size restrictions(larger than 4K), like for device local-memory.
> > +* However in general the final size here should always reflect any
> > +* rounding up, if for example using the
> I915_GEM_CREATE_EXT_MEMORY_REGIONS
> > +* extension to place the object in device local-memory.
> > +*/
> > + __u64 size;
> > + /**
> > +* @handle: Returned handle for the object.
> > +*
> > +* Object handles are nonzero.
> > +*/
> > + __u32 handle;
> > + /**
> > +* @flags: Optional flags.
> > +*
> > +* Supported values:
> > +*
> > +* I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS - Signal to the
> kernel that
> > +* the object will need to be accessed via the CPU.
> > +*
> > +* Only valid when placing objects in I915_MEMORY_CLASS_DEVICE,
> and
> > +* only strictly required on platforms where only some of the device
> > +* memory is directly visible or mappable through the CPU, like on DG2+.
> > +*
> > +* One of the placements MUST also be I915_MEMORY_CLASS_SYSTEM,
> to
> > +* ensure we can always spill the allocation to system memory, if we
> > +* can't place the object in the mappable part of
> > +* I915_MEMORY_CLASS_DEVICE.
> > +*
> > +* Note that buffers that need to be captured with
> EXEC_OBJECT_CAPTURE,
> > +* will need to enable this hint, if the object can also be placed in
> > +* I915_MEMORY_CLASS_DEVICE, starting from DG2+. The execbuf call
> will
> > +* throw an error otherwise. This also means that such objects will need
> > +* I915_MEMORY_CLASS_SYSTEM set as a possible placement.
> > +*
> > +* Without this hint, the kernel will assume that non-mappable
> > +* I915_MEMORY_CLASS_DEVICE is preferred for this object. Note that
> the
> > +* kernel can still migrate the object to the mappable part, as a last
> > +* resort, if userspace ever CPU faults this object, but this might be
> > +* expensive, and so ideally should be avoided.
> > +*/
> > +#define I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS (1 << 0)
> > + __u32 flags;
> > + /**
> > +* @extensions: The chain of extensions to apply to this object.
> > +*
> > +* This will be useful in the future when we need to support several
> > +* different extensions, and we need to apply more than one when
> > +* creating the object. See struct i915_user_extension.
> > +*
> > +* If we don't supply any extensions then we get the same old
> gem_create
> > +* behaviour.
> > +*
> > +* For I915_GEM_CREATE_EXT_MEMORY_REGIONS usage see
> > +* struct drm_i915_gem_create_ext_memory_regions.
> > +*
> > +* For I915_GEM_CREATE_EXT_PROTECT
