[Intel-gfx] [PATCH v2 3/3] drm/i915/huc: improve documentation

[Daniele Ceraolo Spurio]

Better explain the usage of the microcontroller and what i915 is
responsible of. While at it, fix the documentation for the auth
function, which doesn't do any pinning anymore.

v2: add a comment on HuC being optional and descrive how HuC accesses
    memory (Martin)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
Cc: Martin Peres <martin.peres at linux.intel.com>
Acked-by: Anna Karas <anna.karas at intel.com>
---
 Documentation/gpu/i915.rst                | 16 +++++++++--
 drivers/gpu/drm/i915/gt/uc/intel_huc.c    | 33 ++++++++++++++++++++---
 drivers/gpu/drm/i915/gt/uc/intel_huc_fw.c | 15 -----------
 3 files changed, 43 insertions(+), 21 deletions(-)

diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst
index 357e9dfa7de1..60bd6e6403da 100644
--- a/Documentation/gpu/i915.rst
+++ b/Documentation/gpu/i915.rst
@@ -471,8 +471,20 @@ GuC-based command submission
 
 HuC
 ---
-.. kernel-doc:: drivers/gpu/drm/i915/gt/uc/intel_huc_fw.c
-   :doc: HuC Firmware
+.. kernel-doc:: drivers/gpu/drm/i915/gt/uc/intel_huc.c
+   :doc: HuC
+.. kernel-doc:: drivers/gpu/drm/i915/gt/uc/intel_huc.c
+   :functions: intel_huc_auth
+
+HuC Memory Management
+~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/gpu/drm/i915/gt/uc/intel_huc.c
+   :doc: HuC Memory Management
+
+HuC Firmware Layout
+~~~~~~~~~~~~~~~~~~~
+The HuC FW layout is the same as the GuC one, see `GuC Firmware Layout`_
 
 DMC
 ---
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_huc.c b/drivers/gpu/drm/i915/gt/uc/intel_huc.c
index 33608a114d4e..c802e5b68c05 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_huc.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_huc.c
@@ -9,6 +9,32 @@
 #include "intel_huc.h"
 #include "i915_drv.h"
 
+/**
+ * DOC: HuC
+ *
+ * The HuC is a dedicated microcontroller for usage in media HEVC (High
+ * Efficiency Video Coding) operations. Userspace can directly use the firmware
+ * capabilities by adding HuC specific commands to batch buffers.
+ * The kernel driver is only responsible for loading the HuC firmware and
+ * triggering its security authentication, which is performed by the GuC. For
+ * The GuC to correctly perform the authentication, the HuC binary must be
+ * loaded before the GuC one. Loading the HuC is optional; however, not using
+ * the HuC might negatively impact power usage and/or performance of media
+ * workloads, depending on the use-cases.
+ * See https://github.com/intel/media-driver for the latest details on HuC
+ * functionality.
+ */
+
+/**
+ * DOC: HuC Memory Management
+ *
+ * Similarly to the GuC, the HuC can't do any memory allocations on its own,
+ * with the difference being that the allocations for HuC usage are handled by
+ * the userspace driver instead of the kernel one. The HuC accesses the memory
+ * via the PPGTT belonging to the context loaded on the VCS executing the
+ * HuC-specific commands.
+ */
+
 void intel_huc_init_early(struct intel_huc *huc)
 {
 	struct drm_i915_private *i915 = huc_to_gt(huc)->i915;
@@ -118,10 +144,9 @@ void intel_huc_fini(struct intel_huc *huc)
  *
  * Called after HuC and GuC firmware loading during intel_uc_init_hw().
  *
- * This function pins HuC firmware image object into GGTT.
- * Then it invokes GuC action to authenticate passing the offset to RSA
- * signature through intel_guc_auth_huc(). It then waits for 50ms for
- * firmware verification ACK and unpins the object.
+ * This function invokes the GuC action to authenticate the HuC firmware,
+ * passing the offset of the RSA signature to intel_guc_auth_huc(). It then
+ * waits for up to 50ms for firmware verification ACK.
  */
 int intel_huc_auth(struct intel_huc *huc)
 {
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_huc_fw.c b/drivers/gpu/drm/i915/gt/uc/intel_huc_fw.c
index 74602487ed67..d654340d4d03 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_huc_fw.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_huc_fw.c
@@ -7,21 +7,6 @@
 #include "intel_huc_fw.h"
 #include "i915_drv.h"
 
-/**
- * DOC: HuC Firmware
- *
- * Motivation:
- * GEN9 introduces a new dedicated firmware for usage in media HEVC (High
- * Efficiency Video Coding) operations. Userspace can use the firmware
- * capabilities by adding HuC specific commands to batch buffers.
- *
- * Implementation:
- * The same firmware loader is used as the GuC. However, the actual
- * loading to HW is deferred until GEM initialization is done.
- *
- * Note that HuC firmware loading must be done before GuC loading.
- */
-
 /**
  * intel_huc_fw_init_early() - initializes HuC firmware struct
  * @huc: intel_huc struct
-- 
2.23.0