[PATCH v1 3/4] usb: tcpm: print error on hard reset

[Sebastian Reichel]

A USB-PD hard reset involves removing the voltage from VBUS for some
time. So basically it has the same effect as removing the USB-C plug
for a short moment. If the machine is powered from the USB-C port and
does not have a fallback supply (e.g. a battery), this will result in
a full machine reset due to power loss.

Ideally we want to avoid triggering a hard reset on these boards. A
non-working USB-C port is probably better than unplanned reboots. But
boards with a backup supply should do the hard reset to get everything
working again.

In theory it would be enough to check the self_powered property, but
it seems the property might not be configured consistently enough in
system firmwares.

USB-PD hard resets should happen rarely in general, so let's at least
print an error message before the potential board reset happens. This
is also useful, since it immediately gives away which device triggered
the hard reset.

Fixes: 1db4c0ac77e3 ("usb: tcpm: add core framework")
Signed-off-by: Sebastian Reichel <sebastian.reichel at collabora.com>
---
 drivers/usb/tcpm/tcpm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/tcpm/tcpm.c b/drivers/usb/tcpm/tcpm.c
index 786d92fa4c6f..909fe2ef4fcb 100644
--- a/drivers/usb/tcpm/tcpm.c
+++ b/drivers/usb/tcpm/tcpm.c
@@ -1711,6 +1711,8 @@ static void run_state_machine(struct udevice *dev)
 
 	/* Hard_Reset states */
 	case HARD_RESET_SEND:
+		if (!port->self_powered && port->port_type == TYPEC_PORT_SNK)
+			dev_err(dev, "Initiating hard-reset, which might result in machine power-loss.\n");
 		tcpm_pd_transmit(dev, TCPC_TX_HARD_RESET, NULL);
 		tcpm_set_state(dev, HARD_RESET_START, 0);
 		port->wait_dr_swap_message = false;
-- 
2.45.2