[Intel-gfx] [RFC 0/7] drm/i915/pxp: Create a backend abstraction layer for pxp-tee-link

[Teres Alexis, Alan Previn]

++Rodrigo, Daniele, Jani.

Hey folks - any concerns with this approach? 

i915->pxp--->[feature functions]
        |-------> [tee-backends-folder]
                        |--->mei-pxp transport functions (legacy)
                        |--->gsccs transport functions (mtl+)

tee backend folder basically abstracts away the transport mechanism to get PXP messages
to and from PXP firmware service. the goal is to keep the upper layer of PXP somewhat
agnostic to the bottom later and let the bottom later handle backend assets and flows
depending on the platform. 

Today the mei-pxp functions called directly by the pxp main functions and in future to
avoid a whole bunch of "if (genx) else (gen-mtl) i want to create a set of function ptrs
the backend will populate at init (and also a backend-private context) so that the
abstraction can be clean and modular:

struct intel_pxp {
	...
 	struct {
		/** @priv: Pointer exclusively for backend layer to store private context.*/
		void *priv;
		/** @init: Func-ptr called to initialize the backend transport resources.*/
 		int (*init)(struct intel_pxp *pxp);
		/** @fini: Func-ptr called to free the backend transport resources.*/
 		void (*fini)(struct intel_pxp *pxp);
		/**
		 * @is_ready: Func-ptr called to query if the backend transport is available
		 * for use. Depending on the backend, some, such as mei, have asyncronous workers
		 * or callbacks that setup the backend tee link to the security firmware.
		 **/
		bool (*is_ready)(struct intel_pxp *pxp);
		/** @init: Func-ptr called to create a pxp session.*/
 		int (*create_session)(struct intel_pxp *pxp, int session_id);
		/** @init: Func-ptr called to send message packets to pxp firmware.*/
 		int (*send_message)(struct intel_pxp *pxp,
 				    void *msg_in, size_t msg_in_len,
 				    void *msg_out, size_t msg_out_max_len,
	} tee_link;
};

...alan

On Wed, 2022-11-23 at 14:34 -0800, Alan Previn wrote:
> PXP is a feature allowing workloads executing on engines to operate with
> encrypted buffers (via specific state instructions). On the other hand, PXP controls
> for operations like arbitration session creation and global teardown of PXP sessions
> require communicating with the security firmware.
> 
> The transport layer to establish, execute and shutdown communication with the security
> firmware is different between TGL/ADL vs MTL. The former uses the mei component driver
> interfaces while the latter depends on the media-tile's GSC-command-streamer. Both cases
> have very different code flow and assets.
> 
> This series aims to create a clean partition between the front end of the PXP subsystem
> and the backend-tee transport layer. The goal here is to present an intuitive layering
> using backend function pointers that will scale for future hardware backends
> while keeping the front end agnostic to the backend details.
> 
> 
> Alan Previn (7):
>   HAX: drm/i915/pxp: Prepare intel_pxp entry points for MTL
>   drm/i915/pxp: Refactor mei-teelink checks at init/fini
>   drm/i915/pxp: Abstract mei-teelink function access via backend ptrs
>   drm/i915/pxp: Separate tee-link front end interfaces from backend
>     implementation
>   drm/i915/pxp: move mei-pxp and mei-gsc resources to be backend-private
>   drm/i915/pxp: Add PXP gsccs tee-link backend stubs
>   drm/i915/pxp: Better hierarchy readibility - move backends to a
>     backend folder
> 
>  drivers/gpu/drm/i915/Makefile                 |   4 +-
>  .../drm/i915/display/skl_universal_plane.c    |   2 +-
>  drivers/gpu/drm/i915/gem/i915_gem_context.c   |   6 +-
>  drivers/gpu/drm/i915/gem/i915_gem_create.c    |   2 +-
>  .../gpu/drm/i915/gem/i915_gem_execbuffer.c    |   2 +-
>  drivers/gpu/drm/i915/i915_drv.h               |   4 -
>  drivers/gpu/drm/i915/pxp/intel_pxp.c          | 103 +++--
>  drivers/gpu/drm/i915/pxp/intel_pxp.h          |  16 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_cmd.c      |   2 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_debugfs.c  |   8 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_huc.c      |  13 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_irq.c      |   4 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_pm.c       |  11 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_session.c  |   2 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_tee.c      | 310 ++------------
>  drivers/gpu/drm/i915/pxp/intel_pxp_tee.h      |  22 +-
>  drivers/gpu/drm/i915/pxp/intel_pxp_types.h    |  52 ++-
>  .../i915/pxp/tee_backends/intel_pxp_gsccs.c   |  48 +++
>  .../i915/pxp/tee_backends/intel_pxp_gsccs.h   |  13 +
>  .../i915/pxp/tee_backends/intel_pxp_tee_mei.c | 398 ++++++++++++++++++
>  .../i915/pxp/tee_backends/intel_pxp_tee_mei.h |  13 +
>  21 files changed, 677 insertions(+), 358 deletions(-)
>  create mode 100644 drivers/gpu/drm/i915/pxp/tee_backends/intel_pxp_gsccs.c
>  create mode 100644 drivers/gpu/drm/i915/pxp/tee_backends/intel_pxp_gsccs.h
>  create mode 100644 drivers/gpu/drm/i915/pxp/tee_backends/intel_pxp_tee_mei.c
>  create mode 100644 drivers/gpu/drm/i915/pxp/tee_backends/intel_pxp_tee_mei.h
> 
> 
> base-commit: c8b2ce6e20662ef30130e65f473b1ff5362765e3
> -- 
> 2.34.1
>