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 <rogerq@ti.com>
Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>

1 files changed, 83 insertions, 7 deletions

diff --git a/include/linux/usb/otg-fsm.h b/include/linux/usb/otg-fsm.h
index 24198e16f849..8eec0c261be5 100644
--- a/include/linux/usb/otg-fsm.h
+++ b/include/linux/usb/otg-fsm.h
@@ -72,37 +72,113 @@ enum otg_fsm_timer {
         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;
@@ -110,7 +186,7 @@ struct otg_fsm {
         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;