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

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Date: Fri, 31 May 2024 11:47:54 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Sebastian Reichel <sebastian.reichel@...labora.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
	linux-kernel@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH v1 1/1] usb: typec: tcpm: print error on hard reset

On Thu, May 23, 2024 at 07:12:29PM +0200, Sebastian Reichel wrote:
> 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>

Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.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

-- 
heikki