[RFC] drm/i915/uapi/huc: two levels of HuC authentication

[Daniele Ceraolo Spurio]

Starting on DG2, the owner of HuC authentication is the GSC FW. On MTL,
with the GSC moving into the media GT and being loaded by i915, this can
result in a significant delay in HuC readiness on init/resume. To reduce
the impact, the HuC load & authentication has been split in 2 parts:

1) The HuC is loaded via DMA and authenticated by the GuC, like on older
platforms. However, this is now considered a partial authentication and
only allows clear-media workloads.

2) After the GSC FW is loaded, the HuC is re-authenticated with a PXP
command. This is a full authentication and allows all workloads.

This way, only the protected content operations are impacted by the
GSC-introduced delay, which is not an issue because GSC is required
for those anyway.

To report the different steps to userspace, a new value is introduced
for the HuC status ioctl.

RFC: I'm asking for comments ahead of the implementation to make sure
there are no concerns with the proposed interface change. I've kept
value '1' as the "full authentication" mode because that is what it
represents on older platforms. The media driver currently checks for
value != 0, which will keep working for clear-media and allow it to
start submitting without waiting for the GSC auth, while the protected
content side of things will have to adapt to explicitly check for
value == 1 (which will work on existing platforms as well).

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Cc: John Harrison <John.C.Harrison at Intel.com>
Cc: Alan Previn <alan.previn.teres.alexis at intel.com>
Cc: Ankit Jain <ankit1.jain at intel.com>
Cc: Tony Ye <tony.ye at intel.com>
Cc: Carl Zhang <carl.zhang at intel.com>
---
 include/uapi/drm/i915_drm.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 8df261c5ab9b..8a69014f3fd9 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -659,7 +659,8 @@ typedef struct drm_i915_irq_wait {
  * If the IOCTL is successful, the returned parameter will be set to one of the
  * following values:
  *  * 0 if HuC firmware load is not complete,
- *  * 1 if HuC firmware is authenticated and running.
+ *  * 1 if HuC firmware is loaded and fully authenticated,
+ *  * 2 if HuC firmware is loaded and authenticated for clear media only
  */
 #define I915_PARAM_HUC_STATUS		 42
 
-- 
2.37.3