RE: [PATCH 14/14] Doc/gpu/rfc/i915: i915 DG2 uAPI

["Tang, CQ" <cq.tang@intel.com>]

> -----Original Message-----
> From: C, Ramalingam <ramalingam.c@intel.com>
> Sent: Monday, October 11, 2021 9:12 AM
> To: dri-devel <dri-devel@lists.freedesktop.org>; intel-gfx <intel-
> gfx@lists.freedesktop.org>
> Cc: Daniel Vetter <daniel@ffwll.ch>; Auld, Matthew
> <matthew.auld@intel.com>; Tang, CQ <cq.tang@intel.com>; Hellstrom,
> Thomas <thomas.hellstrom@intel.com>; C, Ramalingam
> <ramalingam.c@intel.com>; Daniel Vetter <daniel.vetter@ffwll.ch>
> Subject: [PATCH 14/14] Doc/gpu/rfc/i915: i915 DG2 uAPI
> 
> Details of the new features getting added as part of DG2 enabling and their
> implicit impact on the uAPI.
> 
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> cc: Matthew Auld <matthew.auld@intel.com>
> ---
>  Documentation/gpu/rfc/i915_dg2.rst | 47
> ++++++++++++++++++++++++++++++
>  Documentation/gpu/rfc/index.rst    |  3 ++
>  2 files changed, 50 insertions(+)
>  create mode 100644 Documentation/gpu/rfc/i915_dg2.rst
> 
> diff --git a/Documentation/gpu/rfc/i915_dg2.rst
> b/Documentation/gpu/rfc/i915_dg2.rst
> new file mode 100644
> index 000000000000..a83ca26cd758
> --- /dev/null
> +++ b/Documentation/gpu/rfc/i915_dg2.rst
> @@ -0,0 +1,47 @@
> +====================
> +I915 DG2 RFC Section
> +====================
> +
> +Upstream plan
> +=============
> +Plan to upstream the DG2 enabling is:
> +
> +* Merge basic HW enabling for DG2(Still without pciid)
> +* Merge the 64k support for lmem
> +* Merge the flat CCS enabling patches
> +* Add the pciid for DG2 and enable the DG2 in CI
> +
> +
> +64K page support for lmem
> +=========================
> +On DG2 hw, local-memory supports minimum GTT page size of 64k only. 4k
> is not supported anymore.
> +
> +DG2 hw dont support the 64k(lmem) and 4k(smem) pages in the same
> ppgtt
> +Page table. Refer the struct drm_i915_gem_create_ext for the implication
> of handling the 64k page size.
> +
> +.. kernel-doc:: include/uapi/drm/i915_drm.h
> +        :functions: drm_i915_gem_create_ext
> +
> +
> +flat CCS support for lmem
> +=========================
> +Gen 12+ devices support 3D surfaces compression and compression
> +formats. This is accomplished by an additional compression control state
> (CCS) stored for each surface.

General introduction, OK.

> +
> +Gen 12 devices(TGL and DG1) stores compression state in a separate region
> of memory.
> +It is managed by userspace and has an associated set of userspace
> +managed page tables used by hardware for address translation.

I don't know the purpose of this paragraph, do we need to mention TGL/DG1? This is "Gen 12", not "Gen 12+" in first paragraph.

> +
> +In Gen 12.5 devices(XEXPSDV and DG2) Flat CCS is introduced to replace
> +the userspace managed AUX pagetable with the flat indexed region of
> +device memory for storing the compression state

Because this is DG2 document, do we need to mention XeHP SDV?


> +
> +GOP Driver steals a chunk of memory for the CCS surface corresponding
> +to the entire range of local memory. The memory required for the CCS of
> +the entire local memory is
> +1/256 of the main local memory. The Gop driver will also program a
> +secure register (XEHPSDV_FLAT_CCS_BASE_ADDR 0x4910) with this address
> value.

I think it is not necessary to say the CCS base register. This is internal detail.

> +
> +So the Total local memory available for driver allocation is Total lmem
> +size - CCS data size

Well, we need to minus the GTT, lmem stolen (DG2 only), and WOPCM.  Maybe just say, total local memory available is smaller because of other reserved regions.

> +
> +Flat CCS data needs to be cleared when a lmem object is allocated. And
> +CCS data can be copied in and out of CCS region through
> XY_CTRL_SURF_COPY_BLT.

OK.

--CQ

> diff --git a/Documentation/gpu/rfc/index.rst
> b/Documentation/gpu/rfc/index.rst index 91e93a705230..afb320ed4028
> 100644
> --- a/Documentation/gpu/rfc/index.rst
> +++ b/Documentation/gpu/rfc/index.rst
> @@ -20,6 +20,9 @@ host such documentation:
> 
>      i915_gem_lmem.rst
> 
> +.. toctree::
> +    i915_dg2.rst
> +
>  .. toctree::
> 
>      i915_scheduler.rst
> --
> 2.20.1