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Date:   Mon, 1 Mar 2021 17:19:33 +0200
From:   Heikki Krogerus <heikki.krogerus@linux.intel.com>
To:     Badhri Jagan Sridharan <badhri@google.com>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        Kyle Tso <kyletso@google.com>, stable@vger.kernel.org
Subject: Re: [PATCH v3] usb: typec: tcpm: Wait for vbus discharge to VSAFE0V
 before toggling
Message-ID: <YD0GBW5KkkbG3vg/@kuha.fi.intel.com>
References: <20210225101104.1680697-1-badhri@google.com>
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In-Reply-To: <20210225101104.1680697-1-badhri@google.com>
Precedence: bulk

On Thu, Feb 25, 2021 at 02:11:04AM -0800, 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 makes 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.
> 
> Sink detach:
> [  541.703058] CC1: 3 -> 0, CC2: 0 -> 0 [state SNK_READY, polarity 0, disconnected]
> [  541.703331] Setting voltage/current limit 5000 mV 0 mA
> [  541.727235] VBUS on
> [  541.749650] VBUS off
> [  541.749653] pending state change SNK_READY -> SNK_UNATTACHED @ 650 ms [rev3 NONE_AMS]
> [  541.749944] VBUS VSAFE0V
> [  541.749945] state change SNK_READY -> SNK_UNATTACHED [rev3 NONE_AMS]
> [  541.750806] Disable vbus discharge ret:0
> [  541.907345] Start toggling
> [  541.922799] CC1: 0 -> 0, CC2: 0 -> 0 [state TOGGLING, polarity 0, disconnected]
> 
> Source detach:
> [ 2555.310414] state change SRC_SEND_CAPABILITIES -> SRC_READY [rev3 POWER_NEGOTIATION]
> [ 2555.310675] AMS POWER_NEGOTIATION finished
> [ 2555.310679] cc:=3
> [ 2593.645886] CC1: 0 -> 0, CC2: 2 -> 0 [state SRC_READY, polarity 1, disconnected]
> [ 2593.645919] pending state change SRC_READY -> SNK_UNATTACHED @ 650 ms [rev3 NONE_AMS]
> [ 2593.648419] VBUS off
> [ 2593.648960] VBUS VSAFE0V
> [ 2593.648965] state change SRC_READY -> SNK_UNATTACHED [rev3 NONE_AMS]
> [ 2593.649962] Disable vbus discharge ret:0
> [ 2593.890322] Start toggling
> [ 2593.925663] CC1: 0 -> 0, CC2: 0 -> 0 [state TOGGLING, polarity 0,
> 
> Fixes: f321a02caebd ("usb: typec: tcpm: Implement enabling Auto
> Discharge disconnect support")
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>

Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>

> ---
> Changes since V1:
> - Add Fixes tag
> 
> Changes since V2:
> - Remove VBUS_DISCHARGE state as preferred by Guenter Roeck
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 75 ++++++++++++++++++++++++++++++-----
>  1 file changed, 65 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index be0b6469dd3d..8469c37a59e1 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -438,6 +438,9 @@ struct tcpm_port {
>  	enum tcpm_ams next_ams;
>  	bool in_ams;
>  
> +	/* Auto vbus discharge status */
> +	bool auto_vbus_discharge_enabled;
> +
>  #ifdef CONFIG_DEBUG_FS
>  	struct dentry *dentry;
>  	struct mutex logbuffer_lock;	/* log buffer access lock */
> @@ -507,6 +510,9 @@ static const char * const pd_rev[] = {
>  	(tcpm_port_is_sink(port) && \
>  	((port)->cc1 == TYPEC_CC_RP_3_0 || (port)->cc2 == TYPEC_CC_RP_3_0))
>  
> +#define tcpm_wait_for_discharge(port) \
> +	(((port)->auto_vbus_discharge_enabled && !(port)->vbus_vsafe0v) ? PD_T_SAFE_0V : 0)
> +
>  static enum tcpm_state tcpm_default_state(struct tcpm_port *port)
>  {
>  	if (port->port_type == TYPEC_PORT_DRP) {
> @@ -3413,6 +3419,8 @@ 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 +3503,8 @@ 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 +3578,8 @@ 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));
> @@ -4670,9 +4682,9 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
>  		if (tcpm_port_is_disconnected(port) ||
>  		    !tcpm_port_is_source(port)) {
>  			if (port->port_type == TYPEC_PORT_SRC)
> -				tcpm_set_state(port, SRC_UNATTACHED, 0);
> +				tcpm_set_state(port, SRC_UNATTACHED, tcpm_wait_for_discharge(port));
>  			else
> -				tcpm_set_state(port, SNK_UNATTACHED, 0);
> +				tcpm_set_state(port, SNK_UNATTACHED, tcpm_wait_for_discharge(port));
>  		}
>  		break;
>  	case SNK_UNATTACHED:
> @@ -4703,7 +4715,23 @@ 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))
> +		/*
> +		 * 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.
> +		 *
> +		 * A port that is monitoring the CC voltage for disconnect (but is not in
> +		 * the process of a USB PD PR_Swap or USB PD FR_Swap) shall transition to
> +		 * Unattached.SNK within tSinkDisconnect after the CC voltage remains below
> +		 * vRd-USB for tPDDebounce."
> +		 *
> +		 * 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.
> +		 */
> +		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))
> @@ -4802,9 +4830,13 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
>  		 * Ignore CC changes here.
>  		 */
>  		break;
> -
>  	default:
> -		if (tcpm_port_is_disconnected(port))
> +		/*
> +		 * While acting as sink and auto vbus discharge is enabled, Allow disconnect
> +		 * to be driven by vbus disconnect.
> +		 */
> +		if (tcpm_port_is_disconnected(port) && !(port->pwr_role == TYPEC_SINK &&
> +							 port->auto_vbus_discharge_enabled))
>  			tcpm_set_state(port, unattached_state(port), 0);
>  		break;
>  	}
> @@ -4968,8 +5000,16 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
>  	case SRC_TRANSITION_SUPPLY:
>  	case SRC_READY:
>  	case SRC_WAIT_NEW_CAPABILITIES:
> -		/* Force to unattached state to re-initiate connection */
> -		tcpm_set_state(port, SRC_UNATTACHED, 0);
> +		/*
> +		 * Force to unattached state to re-initiate connection.
> +		 * DRP port should move to Unattached.SNK instead of Unattached.SRC if
> +		 * sink removed. Although sink removal here is due to source's vbus collapse,
> +		 * treat it the same way for consistency.
> +		 */
> +		if (port->port_type == TYPEC_PORT_SRC)
> +			tcpm_set_state(port, SRC_UNATTACHED, tcpm_wait_for_discharge(port));
> +		else
> +			tcpm_set_state(port, SNK_UNATTACHED, tcpm_wait_for_discharge(port));
>  		break;
>  
>  	case PORT_RESET:
> @@ -4988,9 +5028,8 @@ 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)
> +			tcpm_set_state(port, SNK_UNATTACHED, tcpm_wait_for_discharge(port));
>  		break;
>  	}
>  }
> @@ -5012,7 +5051,23 @@ 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 SRC_STARTUP:
> +	case SRC_SEND_CAPABILITIES:
> +	case SRC_SEND_CAPABILITIES_TIMEOUT:
> +	case SRC_NEGOTIATE_CAPABILITIES:
> +	case SRC_TRANSITION_SUPPLY:
> +	case SRC_READY:
> +	case SRC_WAIT_NEW_CAPABILITIES:
> +		if (port->auto_vbus_discharge_enabled) {
> +			if (port->port_type == TYPEC_PORT_SRC)
> +				tcpm_set_state(port, SRC_UNATTACHED, 0);
> +			else
> +				tcpm_set_state(port, SNK_UNATTACHED, 0);
> +		}
> +		break;
>  	default:
> +		if (port->pwr_role == TYPEC_SINK && port->auto_vbus_discharge_enabled)
> +			tcpm_set_state(port, SNK_UNATTACHED, 0);
>  		break;
>  	}
>  }
> -- 
> 2.30.0.617.g56c4b15f3c-goog

thanks,

-- 
heikki