Re: [PATCH v10 13/15] usb: typec: tcpm: Implement enabling Auto Discharge disconnect support

[Heikki Krogerus]

On Wed, Oct 07, 2020 at 11:15:54PM -0700, Badhri Jagan Sridharan wrote:
> TCPCI spec allows TCPC hardware to autonomously discharge the vbus
> capacitance upon disconnect. The expectation is that the TCPM enables
> AutoDischargeDisconnect while entering SNK/SRC_ATTACHED states. Hardware
> then automously discharges vbus when the vbus falls below a certain
> threshold i.e. VBUS_SINK_DISCONNECT_THRESHOLD.
> 
> Apart from enabling the vbus discharge circuit, AutoDischargeDisconnect
> is also used a flag to move TCPCI based TCPC implementations into
> Attached.Snk/Attached.Src state as mentioned in
> Figure 4-15. TCPC State Diagram before a Connection of the
> USB Type-C Port Controller Interface Specification.
> In such TCPC implementations, setting AutoDischargeDisconnect would
> prevent TCPC into entering "Connection_Invalid" state as well.
> 
> Signed-off-by: Badhri Jagan Sridharan <badhri@xxxxxxxxxx>

Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>

> ---
> Changes since v1:
> - Changing patch version to v6 to fix version number confusion.
> 
> Changes since v6:
> - Fixed incorrect data_role error that I introduced by mistake in
>   the previous version.
> 
> Changes since v7:
> - Rebase on usb-next
> 
> Changes since v8:
> - Removing the call to tcpm_set_auto_vbus_discharge_threshold
>   in the source path.
> 
> - Changes since v9:
> - None
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 60 ++++++++++++++++++++++++++++++++---
>  include/linux/usb/tcpm.h      | 15 +++++++++
>  2 files changed, 71 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index d5a3e2b3bea2..51a14d282109 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -1701,6 +1701,24 @@ static void tcpm_handle_alert(struct tcpm_port *port, const __le32 *payload,
>  	}
>  }
>  
> +static int tcpm_set_auto_vbus_discharge_threshold(struct tcpm_port *port,
> +						  enum typec_pwr_opmode mode, bool pps_active,
> +						  u32 requested_vbus_voltage)
> +{
> +	int ret;
> +
> +	if (!port->tcpc->set_auto_vbus_discharge_threshold)
> +		return 0;
> +
> +	ret = port->tcpc->set_auto_vbus_discharge_threshold(port->tcpc, mode, pps_active,
> +							    requested_vbus_voltage);
> +	tcpm_log_force(port,
> +		       "set_auto_vbus_discharge_threshold mode:%d pps_active:%c vbus:%u ret:%d",
> +		       mode, pps_active ? 'y' : 'n', requested_vbus_voltage, ret);
> +
> +	return ret;
> +}
> +
>  static void tcpm_pd_data_request(struct tcpm_port *port,
>  				 const struct pd_message *msg)
>  {
> @@ -1871,6 +1889,10 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
>  						       port->current_limit,
>  						       port->supply_voltage);
>  				port->explicit_contract = true;
> +				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);
>  			} else {
>  				/*
> @@ -2785,8 +2807,12 @@ static int tcpm_src_attach(struct tcpm_port *port)
>  	if (ret < 0)
>  		return ret;
>  
> -	ret = tcpm_set_roles(port, true, TYPEC_SOURCE,
> -			     tcpm_data_role_for_source(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);
> +	}
> +
> +	ret = tcpm_set_roles(port, true, TYPEC_SOURCE, tcpm_data_role_for_source(port));
>  	if (ret < 0)
>  		return ret;
>  
> @@ -2853,6 +2879,12 @@ static void tcpm_unregister_altmodes(struct tcpm_port *port)
>  
>  static void tcpm_reset_port(struct tcpm_port *port)
>  {
> +	int ret;
> +
> +	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);
> +	}
>  	tcpm_unregister_altmodes(port);
>  	tcpm_typec_disconnect(port);
>  	port->attached = false;
> @@ -2917,8 +2949,13 @@ static int tcpm_snk_attach(struct tcpm_port *port)
>  	if (ret < 0)
>  		return ret;
>  
> -	ret = tcpm_set_roles(port, true, TYPEC_SINK,
> -			     tcpm_data_role_for_sink(port));
> +	if (port->tcpc->enable_auto_vbus_discharge) {
> +		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);
> +	}
> +
> +	ret = tcpm_set_roles(port, true, TYPEC_SINK, tcpm_data_role_for_sink(port));
>  	if (ret < 0)
>  		return ret;
>  
> @@ -3502,6 +3539,8 @@ static void run_state_machine(struct tcpm_port *port)
>  		tcpm_set_state(port, SRC_UNATTACHED, PD_T_PS_SOURCE_ON);
>  		break;
>  	case SNK_HARD_RESET_SINK_OFF:
> +		/* Do not discharge/disconnect during hard reseet */
> +		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
>  		memset(&port->pps_data, 0, sizeof(port->pps_data));
>  		tcpm_set_vconn(port, false);
>  		if (port->pd_capable)
> @@ -3544,6 +3583,7 @@ static void run_state_machine(struct tcpm_port *port)
>  			tcpm_set_charge(port, true);
>  		}
>  		tcpm_set_attached_state(port, true);
> +		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, VSAFE5V);
>  		tcpm_set_state(port, SNK_STARTUP, 0);
>  		break;
>  
> @@ -3645,6 +3685,10 @@ static void run_state_machine(struct tcpm_port *port)
>  			tcpm_set_state(port, PR_SWAP_SNK_SRC_SINK_OFF, 0);
>  		break;
>  	case PR_SWAP_SRC_SNK_TRANSITION_OFF:
> +		/*
> +		 * Prevent vbus discharge circuit from turning on during PR_SWAP
> +		 * as this is not a disconnect.
> +		 */
>  		tcpm_set_vbus(port, false);
>  		port->explicit_contract = false;
>  		/* allow time for Vbus discharge, must be < tSrcSwapStdby */
> @@ -3673,9 +3717,17 @@ static void run_state_machine(struct tcpm_port *port)
>  		tcpm_set_state_cond(port, SNK_UNATTACHED, PD_T_PS_SOURCE_ON);
>  		break;
>  	case PR_SWAP_SRC_SNK_SINK_ON:
> +		/* Set the vbus disconnect threshold for implicit contract */
> +		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, VSAFE5V);
>  		tcpm_set_state(port, SNK_STARTUP, 0);
>  		break;
>  	case PR_SWAP_SNK_SRC_SINK_OFF:
> +		/*
> +		 * Prevent vbus discharge circuit from turning on during PR_SWAP
> +		 * as this is not a disconnect.
> +		 */
> +		tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB,
> +						       port->pps_data.active, 0);
>  		tcpm_set_charge(port, false);
>  		tcpm_set_state(port, hard_reset_state(port),
>  			       PD_T_PS_SOURCE_OFF);
> diff --git a/include/linux/usb/tcpm.h b/include/linux/usb/tcpm.h
> index 7303f518ba49..e68aaa12886f 100644
> --- a/include/linux/usb/tcpm.h
> +++ b/include/linux/usb/tcpm.h
> @@ -86,6 +86,18 @@ enum tcpm_transmit_type {
>   * @frs_sourcing_vbus:
>   *		Optional; Called to notify that vbus is now being sourced.
>   *		Low level drivers can perform chip specific operations, if any.
> + * @enable_auto_vbus_discharge:
> + *		Optional; TCPCI spec based TCPC implementations can optionally
> + *		support hardware to autonomously dischrge vbus upon disconnecting
> + *		as sink or source. TCPM signals TCPC to enable the mechanism upon
> + *		entering connected state and signals disabling upon disconnect.
> + * @set_auto_vbus_discharge_threshold:
> + *		Mandatory when enable_auto_vbus_discharge is implemented. TCPM
> + *		calls this function to allow lower levels drivers to program the
> + *		vbus threshold voltage below which the vbus discharge circuit
> + *		will be turned on. requested_vbus_voltage is set to 0 when vbus
> + *		is going to disappear knowingly i.e. during PR_SWAP and
> + *		HARD_RESET etc.
>   */
>  struct tcpc_dev {
>  	struct fwnode_handle *fwnode;
> @@ -113,6 +125,9 @@ struct tcpc_dev {
>  	int (*set_bist_data)(struct tcpc_dev *dev, bool on);
>  	int (*enable_frs)(struct tcpc_dev *dev, bool enable);
>  	void (*frs_sourcing_vbus)(struct tcpc_dev *dev);
> +	int (*enable_auto_vbus_discharge)(struct tcpc_dev *dev, bool enable);
> +	int (*set_auto_vbus_discharge_threshold)(struct tcpc_dev *dev, enum typec_pwr_opmode mode,
> +						 bool pps_active, u32 requested_vbus_voltage);
>  };
>  
>  struct tcpm_port;
> -- 
> 2.28.0.806.g8561365e88-goog

-- 
heikki