drm/i915/pxp: add PXP documentation

Now that all the pieces are in place we can add a description of how the
feature works. Also modify the comments in struct intel_pxp into
kerneldoc.

v2: improve doc (Rodrigo)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210924191452.1539378-17-alan.previn.teres.alexis@intel.com

Documentation/gpu/i915.rst

@@ -474,6 +474,14 @@ Object Tiling IOCTLs
 .. kernel-doc:: drivers/gpu/drm/i915/gem/i915_gem_tiling.c
    :doc: buffer object tiling
 
+Protected Objects
+-----------------
+
+.. kernel-doc:: drivers/gpu/drm/i915/pxp/intel_pxp.c
+   :doc: PXP
+
+.. kernel-doc:: drivers/gpu/drm/i915/pxp/intel_pxp_types.h
+
 Microcontrollers
 ================
 

drivers/gpu/drm/i915/pxp/intel_pxp.c

@@ -11,6 +11,34 @@
 #include "gt/intel_context.h"
 #include "i915_drv.h"
 
+/**
+ * DOC: PXP
+ *
+ * PXP (Protected Xe Path) is a feature available in Gen12 and newer platforms.
+ * It allows execution and flip to display of protected (i.e. encrypted)
+ * objects. The SW support is enabled via the CONFIG_DRM_I915_PXP kconfig.
+ *
+ * Objects can opt-in to PXP encryption at creation time via the
+ * I915_GEM_CREATE_EXT_PROTECTED_CONTENT create_ext flag. For objects to be
+ * correctly protected they must be used in conjunction with a context created
+ * with the I915_CONTEXT_PARAM_PROTECTED_CONTENT flag. See the documentation
+ * of those two uapi flags for details and restrictions.
+ *
+ * Protected objects are tied to a pxp session; currently we only support one
+ * session, which i915 manages and whose index is available in the uapi
+ * (I915_PROTECTED_CONTENT_DEFAULT_SESSION) for use in instructions targeting
+ * protected objects.
+ * The session is invalidated by the HW when certain events occur (e.g.
+ * suspend/resume). When this happens, all the objects that were used with the
+ * session are marked as invalid and all contexts marked as using protected
+ * content are banned. Any further attempt at using them in an execbuf call is
+ * rejected, while flips are converted to black frames.
+ *
+ * Some of the PXP setup operations are performed by the Management Engine,
+ * which is handled by the mei driver; communication between i915 and mei is
+ * performed via the mei_pxp component module.
+ */
+
 struct intel_gt *pxp_to_gt(const struct intel_pxp *pxp)
 {
 	return container_of(pxp, struct intel_gt, pxp);

drivers/gpu/drm/i915/pxp/intel_pxp_types.h

@@ -16,42 +16,65 @@
 struct intel_context;
 struct i915_pxp_component;
 
+/**
+ * struct intel_pxp - pxp state
+ */
 struct intel_pxp {
+	/**
+	 * @pxp_component: i915_pxp_component struct of the bound mei_pxp
+	 * module. Only set and cleared inside component bind/unbind functions,
+	 * which are protected by &tee_mutex.
+	 */
 	struct i915_pxp_component *pxp_component;
+	/**
+	 * @pxp_component_added: track if the pxp component has been added.
+	 * Set and cleared in tee init and fini functions respectively.
+	 */
 	bool pxp_component_added;
 
+	/** @ce: kernel-owned context used for PXP operations */
 	struct intel_context *ce;
 
-	/*
+	/** @arb_mutex: protects arb session start */
+	struct mutex arb_mutex;
+	/**
+	 * @arb_is_valid: tracks arb session status.
 	 * After a teardown, the arb session can still be in play on the HW
 	 * even if the keys are gone, so we can't rely on the HW state of the
 	 * session to know if it's valid and need to track the status in SW.
 	 */
-	struct mutex arb_mutex; /* protects arb session start */
 	bool arb_is_valid;
 
-	/*
-	 * Keep track of which key instance we're on, so we can use it to
-	 * determine if an object was created using the current key or a
+	/**
+	 * @key_instance: tracks which key instance we're on, so we can use it
+	 * to determine if an object was created using the current key or a
 	 * previous one.
 	 */
 	u32 key_instance;
 
-	struct mutex tee_mutex; /* protects the tee channel binding */
+	/** @tee_mutex: protects the tee channel binding and messaging. */
+	struct mutex tee_mutex;
 
-	/*
-	 * If the HW perceives an attack on the integrity of the encryption it
-	 * will invalidate the keys and expect SW to re-initialize the session.
-	 * We keep track of this state to make sure we only re-start the arb
-	 * session when required.
+	/**
+	 * @hw_state_invalidated: if the HW perceives an attack on the integrity
+	 * of the encryption it will invalidate the keys and expect SW to
+	 * re-initialize the session. We keep track of this state to make sure
+	 * we only re-start the arb session when required.
 	 */
 	bool hw_state_invalidated;
 
+	/** @irq_enabled: tracks the status of the kcr irqs */
 	bool irq_enabled;
+	/**
+	 * @termination: tracks the status of a pending termination. Only
+	 * re-initialized under gt->irq_lock and completed in &session_work.
+	 */
 	struct completion termination;
 
+	/** @session_work: worker that manages session events. */
 	struct work_struct session_work;
-	u32 session_events; /* protected with gt->irq_lock */
+	/** @session_events: pending session events, protected with gt->irq_lock. */
+	u32 session_events;
 #define PXP_TERMINATION_REQUEST  BIT(0)
 #define PXP_TERMINATION_COMPLETE BIT(1)
 #define PXP_INVAL_REQUIRED       BIT(2)