linux-kernel - [PATCH v1 1/1] usb: typec: tcpm: print error on hard reset

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Date: Thu, 23 May 2024 19:12:29 +0200
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org
Cc: Guenter Roeck <linux@...ck-us.net>,
	linux-kernel@...r.kernel.org,
	Sebastian Reichel <sebastian.reichel@...labora.com>,
	kernel@...labora.com
Subject: [PATCH v1 1/1] usb: typec: tcpm: print error on hard reset

A USB-C 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.

So let's start with just printing an error message when a hard reset is
triggered on systems we expect to be affected. This at least makes
debugging issues on affected systems easier without impacting unaffected
systems too much.

Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 8a1af08f71b6..375bc84d14a2 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -5185,6 +5185,8 @@ static void run_state_machine(struct tcpm_port *port)
 	case HARD_RESET_SEND:
 		if (port->ams != NONE_AMS)
 			tcpm_ams_finish(port);
+		if (!port->self_powered && port->port_type == TYPEC_PORT_SNK)
+			dev_err(port->dev, "Initiating hard-reset, which might result in machine power-loss.\n");
 		/*
 		 * State machine will be directed to HARD_RESET_START,
 		 * thus set upcoming_state to INVALID_STATE.
-- 
2.43.0