Re: [PATCH] usb: typec: tcpm: Prevent Hard_Reset if Vbus was never low

[Amit Sunil Dhamne <amitsd@google.com>]

Hi Yanik,

On 10/22/24 10:28 AM, Yanik Fuchs wrote:
> Good Evening
>
> Here is a Patch to resolve an issue with TCPM if Vbus was never low.
> Please consider that this is one of my first kernel pull requests, I may have missunderstood the process.
>
> Freundliche Grüsse
> Best regards
>
>
> Yanik Fuchs
>
> ---
>
>  From 604b97b6394b5643394bc63d4ac691c098c99c40 Mon Sep 17 00:00:00 2001
> From: yfu <yanikfuchs@me.com>
> Date: Tue, 22 Oct 2024 18:23:18 +0200
> Subject: [PATCH] usb: typec: tcpm: Prevent Hard_Reset if Vbus was never low
>
> Before this patch, tcpm went into SOFT_RESET state, if Vbus was never low
> resulting in Hard_Reset, if power supply does not support USB_PD Soft_Reset.
>
> In order to prevent this, I remove the Vbus check completely, so that
> we go as well into the SNK_WAIT_CAPABILITIES_TIMEOUT state. There, we send
> PD_CTRL_GET_SOURCE_CAP which many power supply do support.
> (122968f8dda8 usb: typec: tcpm: avoid resets for missing source capability messages)

Please refer to 
https://lore.kernel.org/all/20241024022233.3276995-1-amitsd@google.com/ as
122968f8dda8 is causing USB Type-C PD compliance failures.

>
> Additionally, I added SOFT_RESET (instead of Hard_Reset) as Fallback solution
> if we still not have gotten any capabilities. Hard_Reset is now only done,
> if PD_CTRL_GET_SOURCE_CAP and SOFT_RESET fail to get capabilities.
> ---
>   drivers/usb/typec/tcpm/tcpm.c | 10 ++--------
>   1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index fc619478200f..c7a59c9f78ee 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -5038,14 +5038,8 @@ static void run_state_machine(struct tcpm_port *port)
>   		 * were already in a stable contract before this boot.
>   		 * Do this only once.
>   		 */
> -		if (port->vbus_never_low) {
> -			port->vbus_never_low = false;
> -			tcpm_set_state(port, SNK_SOFT_RESET,
> +		tcpm_set_state(port, SNK_WAIT_CAPABILITIES_TIMEOUT,
>   				       PD_T_SINK_WAIT_CAP);
> -		} else {
> -			tcpm_set_state(port, SNK_WAIT_CAPABILITIES_TIMEOUT,
> -				       PD_T_SINK_WAIT_CAP);
> -		}

Instead of deleting code, please restrict this behavior to non self 
powered battery case as this most likely break compliance and

may break actual use-cases for other users as a result. If you want you 
can move stuff around after

https://lore.kernel.org/all/20241024022233.3276995-1-amitsd@google.com/

gets accepted in the following way:

```

if (!port->self_powered) {

         tcpm_set_state(port, SNK_WAIT_CAPABILITIES_TIMEOUT, 
PD_T_SINK_WAIT_CAP);

         break;

}


if (port->vbus_never_low) {

         tcpm_set_state(port, SNK_SOFT_RESET, PD_T_SINK_WAIT_CAP);

} else {

         tcpm_set_state(port, hard_reset_state(..), PD_T_SINK_WAIT_CAP);

}

```

This way you don't have to execute the SNK_SOFT_RESET flow for non self 
powered use-case.

Thanks,

Amit

>   		break;
>   	case SNK_WAIT_CAPABILITIES_TIMEOUT:
>   		/*
> @@ -5064,7 +5058,7 @@ static void run_state_machine(struct tcpm_port *port)
>   		 * according to the specification.
>   		 */
>   		if (tcpm_pd_send_control(port, PD_CTRL_GET_SOURCE_CAP, TCPC_TX_SOP))
> -			tcpm_set_state_cond(port, hard_reset_state(port), 0);
> +			tcpm_set_state_cond(port, SNK_SOFT_RESET, 0);
>   		else
>   			tcpm_set_state(port, hard_reset_state(port), PD_T_SINK_WAIT_CAP);
>   		break;