usb: otg-fsm: Add documentation for struct otg_fsm

struct otg_fsm is the interface to the OTG state machine.

Document the input, output and internal state variables.
Definations are taken from Table 7-2 and Table 7-4 of
the USB OTG & EH Specification Rev.2.0

Re-arrange some of the members as per use case for more
clarity.

Signed-off-by: Roger Quadros <[e-mail]>
Acked-by: Peter Chen <[e-mail]>
Signed-off-by: Peter Chen <[e-mail]>

include/linux/usb/otg-fsm.h

···
 	NUM_OTG_FSM_TIMERS,
 };
 
-/* OTG state machine according to the OTG spec */
+/**
+ * struct otg_fsm - OTG state machine according to the OTG spec
+ *
+ * OTG hardware Inputs
+ *
+ *	Common inputs for A and B device
+ * @id:		TRUE for B-device, FALSE for A-device.
+ * @adp_change: TRUE when current ADP measurement (n) value, compared to the
+ *		ADP measurement taken at n-2, differs by more than CADP_THR
+ * @power_up:	TRUE when the OTG device first powers up its USB system and
+ *		ADP measurement taken if ADP capable
+ *
+ *	A-Device state inputs
+ * @a_srp_det:	TRUE if the A-device detects SRP
+ * @a_vbus_vld:	TRUE when VBUS voltage is in regulation
+ * @b_conn:	TRUE if the A-device detects connection from the B-device
+ * @a_bus_resume: TRUE when the B-device detects that the A-device is signaling
+ *		  a resume (K state)
+ *	B-Device state inputs
+ * @a_bus_suspend: TRUE when the B-device detects that the A-device has put the
+ *		bus into suspend
+ * @a_conn:	TRUE if the B-device detects a connection from the A-device
+ * @b_se0_srp:	TRUE when the line has been at SE0 for more than the minimum
+ *		time before generating SRP
+ * @b_ssend_srp: TRUE when the VBUS has been below VOTG_SESS_VLD for more than
+ *		 the minimum time before generating SRP
+ * @b_sess_vld:	TRUE when the B-device detects that the voltage on VBUS is
+ *		above VOTG_SESS_VLD
+ * @test_device: TRUE when the B-device switches to B-Host and detects an OTG
+ *		test device. This must be set by host/hub driver
+ *
+ *	Application inputs (A-Device)
+ * @a_bus_drop:	TRUE when A-device application needs to power down the bus
+ * @a_bus_req:	TRUE when A-device application wants to use the bus.
+ *		FALSE to suspend the bus
+ *
+ *	Application inputs (B-Device)
+ * @b_bus_req:	TRUE during the time that the Application running on the
+ *		B-device wants to use the bus
+ *
+ *	Auxilary inputs (OTG v1.3 only. Obsolete now.)
+ * @a_sess_vld:	TRUE if the A-device detects that VBUS is above VA_SESS_VLD
+ * @b_bus_suspend: TRUE when the A-device detects that the B-device has put
+ *		the bus into suspend
+ * @b_bus_resume: TRUE when the A-device detects that the B-device is signaling
+ *		 resume on the bus
+ *
+ * OTG Output status. Read only for users. Updated by OTG FSM helpers defined
+ * in this file
+ *
+ *	Outputs for Both A and B device
+ * @drv_vbus:	TRUE when A-device is driving VBUS
+ * @loc_conn:	TRUE when the local device has signaled that it is connected
+ *		to the bus
+ * @loc_sof:	TRUE when the local device is generating activity on the bus
+ * @adp_prb:	TRUE when the local device is in the process of doing
+ *		ADP probing
+ *
+ *	Outputs for B-device state
+ * @adp_sns:	TRUE when the B-device is in the process of carrying out
+ *		ADP sensing
+ * @data_pulse: TRUE when the B-device is performing data line pulsing
+ *
+ * Internal Variables
+ *
+ * a_set_b_hnp_en: TRUE when the A-device has successfully set the
+ *		b_hnp_enable bit in the B-device.
+ *		   Unused as OTG fsm uses otg->host->b_hnp_enable instead
+ * b_srp_done:	TRUE when the B-device has completed initiating SRP
+ * b_hnp_enable: TRUE when the B-device has accepted the
+ *		SetFeature(b_hnp_enable) B-device.
+ *		Unused as OTG fsm uses otg->gadget->b_hnp_enable instead
+ * a_clr_err:	Asserted (by application ?) to clear a_vbus_err due to an
+ *		overcurrent condition and causes the A-device to transition
+ *		to a_wait_vfall
+ */
 struct otg_fsm {
 	/* Input */
 	int id;
 	int adp_change;
 	int power_up;
-	int test_device;
-	int a_bus_drop;
-	int a_bus_req;
 	int a_srp_det;
 	int a_vbus_vld;
 	int b_conn;
 	int a_bus_resume;
 	int a_bus_suspend;
 	int a_conn;
-	int b_bus_req;
 	int b_se0_srp;
 	int b_ssend_srp;
 	int b_sess_vld;
+	int test_device;
+	int a_bus_drop;
+	int a_bus_req;
+	int b_bus_req;
+
 	/* Auxilary inputs */
 	int a_sess_vld;
 	int b_bus_resume;
 	int b_bus_suspend;
 
 	/* Output */
-	int data_pulse;
 	int drv_vbus;
 	int loc_conn;
 	int loc_sof;
 	int adp_prb;
 	int adp_sns;
+	int data_pulse;
 
 	/* Internal variables */
 	int a_set_b_hnp_en;
···
 	int b_hnp_enable;
 	int a_clr_err;
 
-	/* Informative variables */
+	/* Informative variables. All unused as of now */
 	int a_bus_drop_inf;
 	int a_bus_req_inf;
 	int a_clr_err_inf;