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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH v2] usb: typec: tcpm: Wait for vbus discharge to VSAFE0V
 before toggling
To:     Badhri Jagan Sridharan <badhri@google.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kyle Tso <kyletso@google.com>
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
References: <20210219090409.325492-1-badhri@google.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <c0fbb198-a905-cdd0-3c6e-6af484512a5b@roeck-us.net>
Date:   Fri, 19 Feb 2021 07:56:37 -0800
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On 2/19/21 1:04 AM, Badhri Jagan Sridharan wrote:
> When vbus auto discharge is enabled, TCPM can sometimes be faster than
> the TCPC i.e. TCPM can go ahead and move the port to unattached state
> (involves disabling vbus auto discharge) before TCPC could effectively
> discharge vbus to VSAFE0V. This leaves vbus with residual charge and
> increases the decay time which prevents tsafe0v from being met.
> This change introduces a new state VBUS_DISCHARGE where the TCPM waits
> for a maximum of tSafe0V(max) for vbus to discharge to VSAFE0V before
> transitioning to unattached state and re-enable toggling. If vbus
> discharges to vsafe0v sooner, then, transition to unattached state
> happens right away.
> 
> Also, while in SNK_READY, when auto discharge is enabled, drive
> disconnect based on vbus turning off instead of Rp disappearing on
> CC pins. Rp disappearing on CC pins is almost instanteous compared
> to vbus decay.
> 
> Fixes: f321a02caebd ("usb: typec: tcpm: Implement enabling Auto
> Discharge disconnect support")
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> ---
> Changes since V1:
> - Add Fixes tag
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 60 +++++++++++++++++++++++++++++++----
>  1 file changed, 53 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index be0b6469dd3d..0ed71725980f 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -62,6 +62,8 @@
>  	S(SNK_TRANSITION_SINK_VBUS),		\
>  	S(SNK_READY),				\
>  						\
> +	S(VBUS_DISCHARGE),			\
> +						\
>  	S(ACC_UNATTACHED),			\
>  	S(DEBUG_ACC_ATTACHED),			\
>  	S(AUDIO_ACC_ATTACHED),			\
> @@ -438,6 +440,9 @@ struct tcpm_port {
>  	enum tcpm_ams next_ams;
>  	bool in_ams;
>  
> +	/* Auto vbus discharge state */
> +	bool auto_vbus_discharge_enabled;
> +
>  #ifdef CONFIG_DEBUG_FS
>  	struct dentry *dentry;
>  	struct mutex logbuffer_lock;	/* log buffer access lock */
> @@ -3413,6 +3418,8 @@ static int tcpm_src_attach(struct tcpm_port *port)
>  	if (port->tcpc->enable_auto_vbus_discharge) {
>  		ret = port->tcpc->enable_auto_vbus_discharge(port->tcpc, true);
>  		tcpm_log_force(port, "enable vbus discharge ret:%d", ret);
> +		if (!ret)
> +			port->auto_vbus_discharge_enabled = true;
>  	}
>  
>  	ret = tcpm_set_roles(port, true, TYPEC_SOURCE, tcpm_data_role_for_source(port));
> @@ -3495,6 +3502,8 @@ static void tcpm_reset_port(struct tcpm_port *port)
>  	if (port->tcpc->enable_auto_vbus_discharge) {
>  		ret = port->tcpc->enable_auto_vbus_discharge(port->tcpc, false);
>  		tcpm_log_force(port, "Disable vbus discharge ret:%d", ret);
> +		if (!ret)
> +			port->auto_vbus_discharge_enabled = false;
>  	}
>  	port->in_ams = false;
>  	port->ams = NONE_AMS;
> @@ -3568,6 +3577,8 @@ static int tcpm_snk_attach(struct tcpm_port *port)
>  		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, VSAFE5V);
>  		ret = port->tcpc->enable_auto_vbus_discharge(port->tcpc, true);
>  		tcpm_log_force(port, "enable vbus discharge ret:%d", ret);
> +		if (!ret)
> +			port->auto_vbus_discharge_enabled = true;
>  	}
>  
>  	ret = tcpm_set_roles(port, true, TYPEC_SINK, tcpm_data_role_for_sink(port));
> @@ -3684,6 +3695,12 @@ static void run_state_machine(struct tcpm_port *port)
>  	switch (port->state) {
>  	case TOGGLING:
>  		break;
> +	case VBUS_DISCHARGE:
> +		if (port->port_type == TYPEC_PORT_SRC)
> +			tcpm_set_state(port, SRC_UNATTACHED, PD_T_SAFE_0V);
> +		else
> +			tcpm_set_state(port, SNK_UNATTACHED, PD_T_SAFE_0V);
> +		break;
>  	/* SRC states */
>  	case SRC_UNATTACHED:
>  		if (!port->non_pd_role_swap)
> @@ -4669,7 +4686,9 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
>  	case SRC_READY:
>  		if (tcpm_port_is_disconnected(port) ||
>  		    !tcpm_port_is_source(port)) {
> -			if (port->port_type == TYPEC_PORT_SRC)
> +			if (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v)
> +				tcpm_set_state(port, VBUS_DISCHARGE, 0);
> +			else if (port->port_type == TYPEC_PORT_SRC)
>  				tcpm_set_state(port, SRC_UNATTACHED, 0);
>  			else
>  				tcpm_set_state(port, SNK_UNATTACHED, 0);

Unless I am missing something, the new state is only used to set the
PD_T_SAFE_0V timeout. Is it really necessary/useful to add a new state
just for that, while keeping the rest of if/else statements ?
Personally I would prefer something like
			timeout = (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v) ? PD_T_SAFE_0V : 0;
			if (port->port_type == TYPEC_PORT_SRC)
				tcpm_set_state(port, SRC_UNATTACHED, timeout);
			else
				tcpm_set_state(port, SNK_UNATTACHED, timeout);

In this context, any idea why port_type==TYPEC_PORT_DRP results in
SNK_UNATTACHED state ? That seems a bit odd.

Guenter

> @@ -4703,7 +4722,18 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
>  			tcpm_set_state(port, SNK_DEBOUNCED, 0);
>  		break;
>  	case SNK_READY:
> -		if (tcpm_port_is_disconnected(port))
> +		/*
> +		 * When set_auto_vbus_discharge_threshold is enabled, CC pins go
> +		 * away before vbus decays to disconnect threshold. Allow
> +		 * disconnect to be driven by vbus disconnect when auto vbus
> +		 * discharge is enabled.
> +		 *
> +		 * EXIT condition is based primarily on vbus disconnect and CC is secondary.
> +		 * "A port that has entered into USB PD communications with the Source and
> +		 * has seen the CC voltage exceed vRd-USB may monitor the CC pin to detect
> +		 * cable disconnect in addition to monitoring VBUS.
> +		 */
> +		if (!port->auto_vbus_discharge_enabled && tcpm_port_is_disconnected(port))
>  			tcpm_set_state(port, unattached_state(port), 0);
>  		else if (!port->pd_capable &&
>  			 (cc1 != old_cc1 || cc2 != old_cc2))
> @@ -4803,9 +4833,16 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
>  		 */
>  		break;
>  
> +	case VBUS_DISCHARGE:
> +		/* Do nothing. Waiting for vsafe0v signal */
> +		break;
>  	default:
> -		if (tcpm_port_is_disconnected(port))
> -			tcpm_set_state(port, unattached_state(port), 0);
> +		if (tcpm_port_is_disconnected(port)) {
> +			if (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v)
> +				tcpm_set_state(port, VBUS_DISCHARGE, 0);
> +			else
> +				tcpm_set_state(port, unattached_state(port), 0);
> +		}
>  		break;
>  	}
>  }
> @@ -4988,9 +5025,12 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
>  		break;
>  
>  	default:
> -		if (port->pwr_role == TYPEC_SINK &&
> -		    port->attached)
> -			tcpm_set_state(port, SNK_UNATTACHED, 0);
> +		if (port->pwr_role == TYPEC_SINK && port->attached) {
> +			if (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v)
> +				tcpm_set_state(port, VBUS_DISCHARGE, 0);
> +			else
> +				tcpm_set_state(port, SNK_UNATTACHED, 0);
> +		}
>  		break;
>  	}
>  }
> @@ -5012,6 +5052,12 @@ static void _tcpm_pd_vbus_vsafe0v(struct tcpm_port *port)
>  			tcpm_set_state(port, tcpm_try_snk(port) ? SNK_TRY : SRC_ATTACHED,
>  				       PD_T_CC_DEBOUNCE);
>  		break;
> +	case VBUS_DISCHARGE:
> +		if (port->port_type == TYPEC_PORT_SRC)
> +			tcpm_set_state(port, SRC_UNATTACHED, 0);
> +		else
> +			tcpm_set_state(port, SNK_UNATTACHED, 0);
> +		break;
>  	default:
>  		break;
>  	}
>