linux-kernel - Re: [PATCH v3] usb: typec: tcpm: Relax disconnect threshold during power negotiation

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Date:   Wed, 16 Jun 2021 16:42:31 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Kyle Tso <kyletso@...gle.com>
Cc:     linux@...ck-us.net, gregkh@...uxfoundation.org, badhri@...gle.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] usb: typec: tcpm: Relax disconnect threshold during
 power negotiation

On Wed, Jun 16, 2021 at 05:01:02PM +0800, Kyle Tso wrote:
> If the voltage is being decreased in power negotiation, the Source will
> set the power supply to operate at the new voltage level before sending
> PS_RDY. Relax the threshold before sending Request Message so that it
> will not race with Source which begins to adjust the voltage right after
> it sends Accept Message (PPS) or tSrcTransition (25~35ms) after it sends
> Accept Message (non-PPS).
> 
> The real threshold will be set after Sink receives PS_RDY Message.
> 
> Fixes: f321a02caebd ("usb: typec: tcpm: Implement enabling Auto Discharge disconnect support")
> Cc: Badhri Jagan Sridharan <badhri@...gle.com>
> Signed-off-by: Kyle Tso <kyletso@...gle.com>

Acked-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

> ---
> Changes in v3:
> - move the timing of setting threshold for Fixed RDO as I did for PPS in
>   v2, i.e. move it to tcpm_pd_send_request.
> - add Cc: tag for Badhri
> - update the commit message for the above changes
> 
> Changes in v2:
> - move the timing of setting threshold up to "before sending Request"
>   for PPS power negotiation so that it won't race with the Source.
> - PPS: if it fails to send the Request, fallback to previous threshold
> - PPS: if the Source doesn't respond Accept, fallback to previous
>   threshold
> - update the commit message for above changes
> 
>  drivers/usb/typec/tcpm/tcpm.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 197556038ba4..b1d310ab84c4 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -2604,6 +2604,11 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
>  			} else {
>  				next_state = SNK_WAIT_CAPABILITIES;
>  			}
> +
> +			/* Threshold was relaxed before sending Request. Restore it back. */
> +			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
> +							       port->pps_data.active,
> +							       port->supply_voltage);
>  			tcpm_set_state(port, next_state, 0);
>  			break;
>  		case SNK_NEGOTIATE_PPS_CAPABILITIES:
> @@ -2617,6 +2622,11 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
>  			    port->send_discover)
>  				port->vdm_sm_running = true;
>  
> +			/* Threshold was relaxed before sending Request. Restore it back. */
> +			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
> +							       port->pps_data.active,
> +							       port->supply_voltage);
> +
>  			tcpm_set_state(port, SNK_READY, 0);
>  			break;
>  		case DR_SWAP_SEND:
> @@ -3336,6 +3346,12 @@ static int tcpm_pd_send_request(struct tcpm_port *port)
>  	if (ret < 0)
>  		return ret;
>  
> +	/*
> +	 * Relax the threshold as voltage will be adjusted after Accept Message plus tSrcTransition.
> +	 * It is safer to modify the threshold here.
> +	 */
> +	tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
> +
>  	memset(&msg, 0, sizeof(msg));
>  	msg.header = PD_HEADER_LE(PD_DATA_REQUEST,
>  				  port->pwr_role,
> @@ -3433,6 +3449,9 @@ static int tcpm_pd_send_pps_request(struct tcpm_port *port)
>  	if (ret < 0)
>  		return ret;
>  
> +	/* Relax the threshold as voltage will be adjusted right after Accept Message. */
> +	tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
> +
>  	memset(&msg, 0, sizeof(msg));
>  	msg.header = PD_HEADER_LE(PD_DATA_REQUEST,
>  				  port->pwr_role,
> @@ -4196,6 +4215,10 @@ static void run_state_machine(struct tcpm_port *port)
>  		port->hard_reset_count = 0;
>  		ret = tcpm_pd_send_request(port);
>  		if (ret < 0) {
> +			/* Restore back to the original state */
> +			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
> +							       port->pps_data.active,
> +							       port->supply_voltage);
>  			/* Let the Source send capabilities again. */
>  			tcpm_set_state(port, SNK_WAIT_CAPABILITIES, 0);
>  		} else {
> @@ -4206,6 +4229,10 @@ static void run_state_machine(struct tcpm_port *port)
>  	case SNK_NEGOTIATE_PPS_CAPABILITIES:
>  		ret = tcpm_pd_send_pps_request(port);
>  		if (ret < 0) {
> +			/* Restore back to the original state */
> +			tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
> +							       port->pps_data.active,
> +							       port->supply_voltage);
>  			port->pps_status = ret;
>  			/*
>  			 * If this was called due to updates to sink
> -- 
> 2.32.0.272.g935e593368-goog

-- 
heikki