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Subject: Re: [PATCH v1] tcpm: Honour pSnkStdby requirement during negotiation
To:     Badhri Jagan Sridharan <badhri@google.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        --validate@google.com
References: <20200804065111.3889122-1-badhri@google.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Date:   Tue, 4 Aug 2020 09:58:57 -0700
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On 8/3/20 11:51 PM, Badhri Jagan Sridharan wrote:
>>From PD Spec:
> The Sink Shall transition to Sink Standby before a positive or
> negative voltage transition of VBUS. During Sink Standby
> the Sink Shall reduce its power draw to pSnkStdby. This allows
> the Source to manage the voltage transition as well as
> supply sufficient operating current to the Sink to maintain PD
> operation during the transition. The Sink Shall
> complete this transition to Sink Standby within tSnkStdby
> after evaluating the Accept Message from the Source. The
> transition when returning to Sink operation from Sink Standby
> Shall be completed within tSnkNewPower. The
> pSnkStdby requirement Shall only apply if the Sink power draw
> is higher than this level.
> 
> The above requirement needs to be met to prevent hard resets
> from port partner.
> 
> Introducing psnkstdby_after_accept flag to accommodate systems
> where the input current limit loops are not fast enough to meet
> tSnkStby(15 msec).
> 
> When not set, port requests PD_P_SNK_STDBY upon entering SNK_DISCOVERY and
> the actual currrent limit after RX of PD_CTRL_PSRDY for PD link,
> SNK_READY for non-pd link.
> 
> When set, port requests CC advertisement based current limit during
> SNK_DISCOVERY, current gets limited to PD_P_SNK_STDBY during
> SNK_TRANSITION_SINK, PD based current limit gets set after RX of
> PD_CTRL_PSRDY. However, in this case it has to be made sure that the
> tSnkStdby (15 msec) is met.
> 
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> ---
>  drivers/usb/typec/tcpm/tcpm.c | 52 +++++++++++++++++++++++++++--------
>  include/linux/usb/pd.h        |  5 +++-
>  2 files changed, 44 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 3ef37202ee37..e46da41940b9 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -293,9 +293,12 @@ struct tcpm_port {
>  	unsigned int operating_snk_mw;
>  	bool update_sink_caps;
>  
> -	/* Requested current / voltage */
> +	/* Set current / voltage */
>  	u32 current_limit;
>  	u32 supply_voltage;
> +	/* current / voltage requested to partner */
> +	u32 req_current_limit;
> +	u32 req_supply_voltage;

I don't see a clear delineation where, when, and why supply_voltage vs. req_supply_voltage
and current_limit vs. req_current_limit is used. Maybe someone else does and can give a
Reviewed-by: tag, but for my part I'll have to spend some time trying to understand
what each variable and its use now means. Overall this suggests that the code may now be
a bit fragile. If those two sets of variables are now indeed needed, I think it would help
to have a detailed explanation for each use. This would help reducing the probability
of errors if the code has to be touched again in the future.

>  
>  	/* Used to export TA voltage and current */
>  	struct power_supply *psy;
> @@ -323,13 +326,27 @@ struct tcpm_port {
>  	struct pd_mode_data mode_data;
>  	struct typec_altmode *partner_altmode[ALTMODE_DISCOVERY_MAX];
>  	struct typec_altmode *port_altmode[ALTMODE_DISCOVERY_MAX];
> -
>  	/* Deadline in jiffies to exit src_try_wait state */
>  	unsigned long max_wait;
>  
>  	/* port belongs to a self powered device */
>  	bool self_powered;
>  
> +	/*
> +	 * Honour psnkstdby after accept is received.
> +	 * However, in this case it has to be made sure that the tSnkStdby (15
> +	 * msec) is met.
> +	 *
> +	 * When not set, port requests PD_P_SNK_STDBY_5V upon entering SNK_DISCOVERY and
> +	 * the actual currrent limit after RX of PD_CTRL_PSRDY for PD link,
> +	 * SNK_READY for non-pd link.
> +	 *
> +	 * When set, port requests CC advertisement based current limit during
> +	 * SNK_DISCOVERY, current gets limited to PD_P_SNK_STDBY_5V during SNK_TRANSITION_SINK,
> +	 * PD based current limit gets set after RX of PD_CTRL_PSRDY.
> +	 */
> +	bool psnkstdby_after_accept;
> +
>  #ifdef CONFIG_DEBUG_FS
>  	struct dentry *dentry;
>  	struct mutex logbuffer_lock;	/* log buffer access lock */
> @@ -1787,9 +1804,8 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
>  		switch (port->state) {
>  		case SNK_TRANSITION_SINK:
>  			if (port->vbus_present) {
> -				tcpm_set_current_limit(port,
> -						       port->current_limit,
> -						       port->supply_voltage);
> +				tcpm_set_current_limit(port, port->req_current_limit,
> +						       port->req_supply_voltage);
>  				port->explicit_contract = true;
>  				tcpm_set_state(port, SNK_READY, 0);
>  			} else {
> @@ -1861,8 +1877,8 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
>  			break;
>  		case SNK_NEGOTIATE_PPS_CAPABILITIES:
>  			port->pps_data.active = true;
> -			port->supply_voltage = port->pps_data.out_volt;
> -			port->current_limit = port->pps_data.op_curr;
> +			port->req_supply_voltage = port->pps_data.out_volt;
> +			port->req_current_limit = port->pps_data.op_curr;
>  			tcpm_set_state(port, SNK_TRANSITION_SINK, 0);
>  			break;
>  		case SOFT_RESET_SEND:
> @@ -2463,8 +2479,8 @@ static int tcpm_pd_build_request(struct tcpm_port *port, u32 *rdo)
>  			 flags & RDO_CAP_MISMATCH ? " [mismatch]" : "");
>  	}
>  
> -	port->current_limit = ma;
> -	port->supply_voltage = mv;
> +	port->req_current_limit = ma;
> +	port->req_supply_voltage = mv;
>  
>  	return 0;
>  }
> @@ -3235,9 +3251,11 @@ 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);
> +			if (port->psnkstdby_after_accept || tcpm_get_current_limit(port) <=
> +			    PD_P_SNK_STDBY_5V)
> +				tcpm_set_current_limit(port, tcpm_get_current_limit(port), 5000);
> +			else
> +				tcpm_set_current_limit(port, PD_P_SNK_STDBY_5V, 5000);
>  			tcpm_set_charge(port, true);
>  			tcpm_set_state(port, SNK_WAIT_CAPABILITIES, 0);
>  			break;
> @@ -3318,6 +3336,10 @@ static void run_state_machine(struct tcpm_port *port)
>  		}
>  		break;
>  	case SNK_TRANSITION_SINK:
> +		if (port->psnkstdby_after_accept)
> +			tcpm_set_current_limit(port, tcpm_get_current_limit(port) >
> +					       PD_P_SNK_STDBY_5V ? PD_P_SNK_STDBY_5V :
> +					       tcpm_get_current_limit(port), 5000);
>  	case SNK_TRANSITION_SINK_VBUS:
>  		tcpm_set_state(port, hard_reset_state(port),
>  			       PD_T_PS_TRANSITION);
> @@ -3331,6 +3353,10 @@ static void run_state_machine(struct tcpm_port *port)
>  			port->pwr_opmode = TYPEC_PWR_MODE_PD;
>  		}
>  
> +		/* Set current limit for NON-PD link when psnkstdby_after_accept is not set*/
> +		if (!port->pd_capable && !port->psnkstdby_after_accept)
> +			tcpm_set_current_limit(port, tcpm_get_current_limit(port), 5000);
> +
>  		tcpm_swap_complete(port, 0);
>  		tcpm_typec_connect(port);
>  		tcpm_check_send_discover(port);
> @@ -4513,6 +4539,8 @@ static int tcpm_fw_get_caps(struct tcpm_port *port,
>  	port->typec_caps.type = ret;
>  	port->port_type = port->typec_caps.type;
>  
> +	port->psnkstdby_after_accept = fwnode_property_read_bool(fwnode, "psnkstdby-after-accept");
> +

I think this will need to be documented.

Guenter

>  	if (port->port_type == TYPEC_PORT_SNK)
>  		goto sink;
>  
> diff --git a/include/linux/usb/pd.h b/include/linux/usb/pd.h
> index b6c233e79bd4..6bd70f77045e 100644
> --- a/include/linux/usb/pd.h
> +++ b/include/linux/usb/pd.h
> @@ -483,5 +483,8 @@ static inline unsigned int rdo_max_power(u32 rdo)
>  #define PD_N_CAPS_COUNT		(PD_T_NO_RESPONSE / PD_T_SEND_SOURCE_CAP)
>  #define PD_N_HARD_RESET_COUNT	2
>  
> -#define PD_T_BIST_CONT_MODE	50 /* 30 - 60 ms */
> +#define PD_T_BIST_CONT_MODE	50	/* 30 - 60 ms */
> +
> +#define PD_P_SNK_STDBY_5V	500	/* 2500 mw - 500mA @ 5V */
> +
>  #endif /* __LINUX_USB_PD_H */
>