[PATCH v3 1/3] usb: typec: tcpm: Honour pSnkStdby requirement during negotiation

[Badhri Jagan Sridharan <badhri@google.com>]

From PD Spec:
The Sink Shall transition to Sink Standby before a positive or
negative voltage transition of VBUS. During Sink Standby
the Sink Shall reduce its power draw to pSnkStdby. This allows
the Source to manage the voltage transition as well as
supply sufficient operating current to the Sink to maintain PD
operation during the transition. The Sink Shall
complete this transition to Sink Standby within tSnkStdby
after evaluating the Accept Message from the Source. The
transition when returning to Sink operation from Sink Standby
Shall be completed within tSnkNewPower. The
pSnkStdby requirement Shall only apply if the Sink power draw
is higher than this level.

The above requirement needs to be met to prevent hard resets
from port partner.

Without the patch: (5V/3A during SNK_DISCOVERY all the way through
explicit contract)
[   95.711984] CC1: 0 -> 0, CC2: 0 -> 5 [state TOGGLING, polarity 0, connected]
[   95.712007] state change TOGGLING -> SNK_ATTACH_WAIT [rev3 NONE_AMS]
[   95.712017] pending state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED @ 170 ms [rev3 NONE_AMS]
[   95.837190] VBUS on
[   95.882075] state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED [delayed 170 ms]
[   95.882082] state change SNK_DEBOUNCED -> SNK_ATTACHED [rev3 NONE_AMS]
[   95.882086] polarity 1
[   95.883151] set_auto_vbus_discharge_threshold mode:0 pps_active:n vbus:5000 ret:0
[   95.883441] enable vbus discharge ret:0
[   95.883445] Requesting mux state 1, usb-role 2, orientation 2
[   95.883776] state change SNK_ATTACHED -> SNK_STARTUP [rev3 NONE_AMS]
[   95.883879] pending state change SNK_STARTUP -> SNK_DISCOVERY @ 500 ms [rev3 NONE_AMS]
[   96.038960] VBUS on
[   96.383939] state change SNK_STARTUP -> SNK_DISCOVERY [delayed 500 ms]
[   96.383946] Setting voltage/current limit 5000 mV 3000 mA
[   96.383961] vbus=0 charge:=1
[   96.386044] state change SNK_DISCOVERY -> SNK_WAIT_CAPABILITIES [rev3 NONE_AMS]
[   96.386309] pending state change SNK_WAIT_CAPABILITIES -> HARD_RESET_SEND @ 450 ms [rev3 NONE_AMS]
[   96.394404] PD RX, header: 0x2161 [1]
[   96.394408]  PDO 0: type 0, 5000 mV, 3000 mA [E]
[   96.394410]  PDO 1: type 0, 9000 mV, 2000 mA []
[   96.394412] state change SNK_WAIT_CAPABILITIES -> SNK_NEGOTIATE_CAPABILITIES [rev2 POWER_NEGOTIATION]
[   96.394416] Setting usb_comm capable false
[   96.395083] cc=0 cc1=0 cc2=5 vbus=0 vconn=sink polarity=1
[   96.395089] Requesting PDO 1: 9000 mV, 2000 mA
[   96.395093] PD TX, header: 0x1042
[   96.397404] PD TX complete, status: 0
[   96.397424] pending state change SNK_NEGOTIATE_CAPABILITIES -> HARD_RESET_SEND @ 60 ms [rev2 POWER_NEGOTIATION]
[   96.400826] PD RX, header: 0x363 [1]
[   96.400829] state change SNK_NEGOTIATE_CAPABILITIES -> SNK_TRANSITION_SINK [rev2 POWER_NEGOTIATION]
[   96.400832] pending state change SNK_TRANSITION_SINK -> HARD_RESET_SEND @ 500 ms [rev2 POWER_NEGOTIATION]
[   96.577315] PD RX, header: 0x566 [1]
[   96.577321] Setting voltage/current limit 9000 mV 2000 mA
[   96.578363] set_auto_vbus_discharge_threshold mode:3 pps_active:n vbus:9000 ret:0
[   96.578370] state change SNK_TRANSITION_SINK -> SNK_READY [rev2 POWER_NEGOTIATION]

With the patch:
[  168.398573] CC1: 0 -> 0, CC2: 0 -> 5 [state TOGGLING, polarity 0, connected]
[  168.398605] state change TOGGLING -> SNK_ATTACH_WAIT [rev3 NONE_AMS]
[  168.398619] pending state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED @ 170 ms [rev3 NONE_AMS]
[  168.522348] VBUS on
[  168.568676] state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED [delayed 170 ms]
[  168.568684] state change SNK_DEBOUNCED -> SNK_ATTACHED [rev3 NONE_AMS]
[  168.568688] polarity 1
[  168.569867] set_auto_vbus_discharge_threshold mode:0 pps_active:n vbus:5000 ret:0
[  168.570158] enable vbus discharge ret:0
[  168.570161] Requesting mux state 1, usb-role 2, orientation 2
[  168.570504] state change SNK_ATTACHED -> SNK_STARTUP [rev3 NONE_AMS]
[  168.570634] pending state change SNK_STARTUP -> SNK_DISCOVERY @ 500 ms [rev3 NONE_AMS]
[  169.070689] state change SNK_STARTUP -> SNK_DISCOVERY [delayed 500 ms]
[  169.070695] Setting voltage/current limit 5000 mV 3000 mA
[  169.070702] vbus=0 charge:=1
[  169.072719] state change SNK_DISCOVERY -> SNK_WAIT_CAPABILITIES [rev3 NONE_AMS]
[  169.073145] pending state change SNK_WAIT_CAPABILITIES -> HARD_RESET_SEND @ 450 ms [rev3 NONE_AMS]
[  169.077162] PD RX, header: 0x2161 [1]
[  169.077172]  PDO 0: type 0, 5000 mV, 3000 mA [E]
[  169.077178]  PDO 1: type 0, 9000 mV, 2000 mA []
[  169.077183] state change SNK_WAIT_CAPABILITIES -> SNK_NEGOTIATE_CAPABILITIES [rev2 POWER_NEGOTIATION]
[  169.077191] Setting usb_comm capable false
[  169.077753] cc=0 cc1=0 cc2=5 vbus=0 vconn=sink polarity=1
[  169.077759] Requesting PDO 1: 9000 mV, 2000 mA
[  169.077762] PD TX, header: 0x1042
[  169.079990] PD TX complete, status: 0
[  169.080013] pending state change SNK_NEGOTIATE_CAPABILITIES -> HARD_RESET_SEND @ 60 ms [rev2 POWER_NEGOTIATION]
[  169.083183] VBUS on
[  169.084195] PD RX, header: 0x363 [1]
[  169.084200] state change SNK_NEGOTIATE_CAPABILITIES -> SNK_TRANSITION_SINK [rev2 POWER_NEGOTIATION]
[  169.084206] Setting standby current 5000 mV @ 500 mA
[  169.084209] Setting voltage/current limit 5000 mV 500 mA
[  169.084220] pending state change SNK_TRANSITION_SINK -> HARD_RESET_SEND @ 500 ms [rev2 POWER_NEGOTIATION]
[  169.260222] PD RX, header: 0x566 [1]
[  169.260227] Setting voltage/current limit 9000 mV 2000 mA
[  169.261315] set_auto_vbus_discharge_threshold mode:3 pps_active:n vbus:9000 ret:0
[  169.261321] state change SNK_TRANSITION_SINK -> SNK_READY [rev2 POWER_NEGOTIATION]
[  169.261570] AMS POWER_NEGOTIATION finished

Fixes: f0690a25a140b ("staging: typec: USB Type-C Port Manager (tcpm)")
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
---
Changes since V2:
* Refactored code based on Heikki's suggestion
* Added reviewed-by tag from Guenter
---
 drivers/usb/typec/tcpm/tcpm.c | 17 +++++++++++++++++
 include/linux/usb/pd.h        |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 1c32bdf62852..aedc8bb9532a 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -4131,6 +4131,23 @@ static void run_state_machine(struct tcpm_port *port)
 		}
 		break;
 	case SNK_TRANSITION_SINK:
+		/* From the USB PD spec:
+		 * "The Sink Shall transition to Sink Standby before a positive or
+		 * negative voltage transition of VBUS. During Sink Standby
+		 * the Sink Shall reduce its power draw to pSnkStdby."
+		 *
+		 * This is not applicable to PPS though as the port can continue
+		 * to draw negotiated power without switching to standby.
+		 */
+		if (port->supply_voltage != port->req_supply_voltage && !port->pps_data.active &&
+		    port->current_limit * port->supply_voltage / 1000 > PD_P_SNK_STDBY_MW) {
+			u32 stdby_ma = PD_P_SNK_STDBY_MW * 1000 / port->supply_voltage;
+
+			tcpm_log(port, "Setting standby current %u mV @ %u mA",
+				 port->supply_voltage, stdby_ma);
+			tcpm_set_current_limit(port, stdby_ma, port->supply_voltage);
+		}
+		fallthrough;
 	case SNK_TRANSITION_SINK_VBUS:
 		tcpm_set_state(port, hard_reset_state(port),
 			       PD_T_PS_TRANSITION);
diff --git a/include/linux/usb/pd.h b/include/linux/usb/pd.h
index 70d681918d01..bf00259493e0 100644
--- a/include/linux/usb/pd.h
+++ b/include/linux/usb/pd.h
@@ -493,4 +493,6 @@ static inline unsigned int rdo_max_power(u32 rdo)
 #define PD_N_CAPS_COUNT		(PD_T_NO_RESPONSE / PD_T_SEND_SOURCE_CAP)
 #define PD_N_HARD_RESET_COUNT	2
 
+#define PD_P_SNK_STDBY_MW	2500	/* 2500 mW */
+
 #endif /* __LINUX_USB_PD_H */
-- 
2.31.1.295.g9ea45b61b8-goog