staging: vchiq_arm: Add TODO for some explanations

There is still an open TODO about some high-level descriptions
mostly related to the VideoCore interface (ABI, IOCTL) and the
thread architecture. This should be more helpful than a separate
document describing VCHIQ.

Signed-off-by: Stefan Wahren <[email protected]>

Author: lategoodbye

drivers/staging/vc04_services/Documentation/vchiq-cdev

@@ -0,0 +1,45 @@
+What:		/dev/vchiq
+Date:		October 2016
+KernelVersion:	4.9
+Contact:	[email protected]
+Description:
+		The ioctl interface for the VCHIQ character device.
+		Following actions are supported:
+
+		/* TODO: Please explain each IOCTL in short */
+
+		* VCHIQ_IOC_CONNECT:
+
+		* VCHIQ_IOC_SHUTDOWN:
+
+		* VCHIQ_IOC_CREATE_SERVICE:
+
+		* VCHIQ_IOC_REMOVE_SERVICE:
+
+		* VCHIQ_IOC_QUEUE_MESSAGE:
+
+		* VCHIQ_IOC_QUEUE_BULK_TRANSMIT:
+
+		* VCHIQ_IOC_QUEUE_BULK_RECEIVE:
+
+		* VCHIQ_IOC_AWAIT_COMPLETION:
+
+		* VCHIQ_IOC_DEQUEUE_MESSAGE:
+
+		* VCHIQ_IOC_GET_CLIENT_ID:
+
+		* VCHIQ_IOC_GET_CONFIG:
+
+		* VCHIQ_IOC_CLOSE_SERVICE:
+
+		* VCHIQ_IOC_USE_SERVICE:
+
+		* VCHIQ_IOC_RELEASE_SERVICE:
+
+		* VCHIQ_IOC_SET_SERVICE_OPTION:
+
+		* VCHIQ_IOC_DUMP_PHYS_MEM:
+
+		* VCHIQ_IOC_LIB_VERSION:
+
+		* VCHIQ_IOC_CLOSE_DELIVERED:

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c

@@ -83,6 +83,9 @@ static const struct vchiq_platform_info bcm2711_info = {
 
 struct vchiq_arm_state {
 	/* Keepalive-related data */
+	/* TODO: Please elaborate the purpose of this thread
+	 * What needs to be kept alive?
+	 */
 	struct task_struct *ka_thread;
 	struct completion ka_evt;
 	atomic_t ka_use_count;

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h

@@ -174,6 +174,7 @@ struct vchiq_slot_info {
 	short release_count;
 };
 
+/* TODO: Please explain the meaning of "service" in the context of VCHIQ */
 struct vchiq_service {
 	struct vchiq_service_base base;
 	unsigned int handle;
@@ -289,6 +290,10 @@ struct vchiq_shared_state {
 	int debug[DEBUG_MAX];
 };
 
+/*
+ * TODO: Mark all structs which are shared with the VideoCore and must not
+ * be modified (ABI)
+ */
 struct vchiq_slot_zero {
 	int magic;
 	short version;
@@ -325,12 +330,17 @@ struct vchiq_state {
 	struct vchiq_instance **instance;
 
 	/* Processes incoming messages */
+	/* TODO: This is the only thread which handles incoming messages
+	 *       or just asynchronous messages ?
+	 */
 	struct task_struct *slot_handler_thread;
 
 	/* Processes recycled slots */
+	/* TODO: Please elaborate more ... (purpose) */
 	struct task_struct *recycle_thread;
 
 	/* Processes synchronous messages */
+	/* TODO: Please elaborate more ... (direction, purpose) */
 	struct task_struct *sync_thread;
 
 	/* Local implementation of the trigger remote event */