Re: [PATCH v2 5/6] usb: typec: tcpm: Allow slow charging loops to comply to pSnkStby

[Heikki Krogerus]

On Wed, Apr 07, 2021 at 01:07:22PM -0700, Badhri Jagan Sridharan wrote:
> When a PD charger advertising Rp-3.0 is connected to a sink port, the
> sink port current limit would 3A, during SNK_DISCOVERY, till power
> negotiation starts. Once the negotiation starts the power limit needs
> to drop down to pSnkStby(500mA @ 5V) and to negotiated current limit
> once the explicit contract is in place. Not all charging loops can ramp
> up to 3A and drop down to 500mA within tSnkStdby which is 15ms. The port
> partner might hard reset if tSnkStdby is not met.
> 
> To solve this problem, this patch introduces slow-charger-loop which
> when set makes the port request PD_P_SNK_STDBY_MW upon entering
> SNK_DISCOVERY(instead of 3A or the 1.5A during SNK_DISCOVERY) and the
> actual currrent limit after RX of PD_CTRL_PSRDY for PD link or during
> SNK_READY for non-pd link.
> 
> Signed-off-by: Badhri Jagan Sridharan <badhri@xxxxxxxxxx>
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 770b2edd9a04..b5bed6866a2b 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -459,6 +459,12 @@ struct tcpm_port {
>  	/* Auto vbus discharge status */
>  	bool auto_vbus_discharge_enabled;
>  
> +	/*
> +	 * When set, port requests PD_P_SNK_STDBY_MW upon entering SNK_DISCOVERY and
> +	 * the actual currrent limit after RX of PD_CTRL_PSRDY for PD link,
> +	 * SNK_READY for non-pd link.
> +	 */
> +	bool slow_charger_loop;
>  #ifdef CONFIG_DEBUG_FS
>  	struct dentry *dentry;
>  	struct mutex logbuffer_lock;	/* log buffer access lock */
> @@ -4047,9 +4053,12 @@ static void run_state_machine(struct tcpm_port *port)
>  		break;
>  	case SNK_DISCOVERY:
>  		if (port->vbus_present) {
> -			tcpm_set_current_limit(port,
> -					       tcpm_get_current_limit(port),
> -					       5000);
> +			u32 current_lim = (!port->slow_charger_loop ||
> +					   (tcpm_get_current_limit(port) <=
> +					    PD_P_SNK_STDBY_MW / 5)) ?
> +				tcpm_get_current_limit(port) :
> +				PD_P_SNK_STDBY_MW / 5;

Here the use of the ternary operator is not appropriate. Please try to
clean that up somehow. Maybe something like this would be better?

                        u32 current_lim = tcpm_get_current_limit(port);

			if (port->slow_charger_loop || (current_lim < PD_P_SNK_STDBY_MW / 5))
				current_lim = PD_P_SNK_STDBY_MW / 5;

> +			tcpm_set_current_limit(port, current_lim, 5000);
>  			tcpm_set_charge(port, true);
>  			tcpm_set_state(port, SNK_WAIT_CAPABILITIES, 0);
>  			break;
> @@ -4161,6 +4170,8 @@ static void run_state_machine(struct tcpm_port *port)
>  			port->pwr_opmode = TYPEC_PWR_MODE_PD;
>  		}
>  
> +		if (!port->pd_capable && port->slow_charger_loop)
> +			tcpm_set_current_limit(port, tcpm_get_current_limit(port), 5000);
>  		tcpm_swap_complete(port, 0);
>  		tcpm_typec_connect(port);
>  		mod_enable_frs_delayed_work(port, 0);
> @@ -5763,6 +5774,7 @@ static int tcpm_fw_get_caps(struct tcpm_port *port,
>  	port->typec_caps.type = ret;
>  	port->port_type = port->typec_caps.type;
>  
> +	port->slow_charger_loop = fwnode_property_read_bool(fwnode, "slow-charger-loop");
>  	if (port->port_type == TYPEC_PORT_SNK)
>  		goto sink;
>  
> -- 
> 2.31.1.295.g9ea45b61b8-goog

thanks,

-- 
heikki