Re: [PATCH 3/6] staging: usb: tcpm: usb: typec: tcpm: Prevent TCPM from looping in SRC_TRYWAIT

[Guenter Roeck]

On Sat, Aug 26, 2017 at 10:24:31PM -0700, Badhri Jagan Sridharan wrote:
> According to the spec the following is the condition
> for exiting TryWait.SRC:
> 
> "The port shall transition to Attached.SRC when V BUS is at vSafe0V
> and the SRC.Rd state is detected on exactly one of the CC pins for at
> least tCCDebounce. The port shall transition to Unattached.SNK after
> tDRPTry if neither of the CC1 or CC2 pins are in the SRC.Rd state"
> 
> TCPM at present keeps re-entering the SRC_TRYWAIT and keeps restarting
> tDRPTry if the CC presents Rp and disconnects within tCCDebounce.
> 
> For example:
> [  447.164308] pending state change SRC_TRYWAIT -> SRC_ATTACHED @ 200 ms
> [  447.164386] CC1: 2 -> 0, CC2: 0 -> 0 [state SRC_TRYWAIT, polarity 0, disconnected]
> [  447.164406] state change SRC_TRYWAIT -> SRC_TRYWAIT
> [  447.164573] cc:=3
> [  447.191408] pending state change SRC_TRYWAIT -> SRC_TRYWAIT_UNATTACHED @ 100 ms
> [  447.191478] CC1: 0 -> 0, CC2: 0 -> 0 [state SRC_TRYWAIT, polarity 0, disconnected]
> [  447.207261] CC1: 0 -> 2, CC2: 0 -> 0 [state SRC_TRYWAIT, polarity 0, connected]
> [  447.207306] state change SRC_TRYWAIT -> SRC_TRYWAIT
> [  447.207485] cc:=3
> [  447.237283] pending state change SRC_TRYWAIT -> SRC_ATTACHED @ 200 ms
> [  447.237357] CC1: 2 -> 0, CC2: 0 -> 0 [state SRC_TRYWAIT, polarity 0, disconnected]
> [  447.237379] state change SRC_TRYWAIT -> SRC_TRYWAIT
> [  447.237532] cc:=3
> [  447.263219] pending state change SRC_TRYWAIT -> SRC_TRYWAIT_UNATTACHED @ 100 ms
> [  447.263289] CC1: 0 -> 0, CC2: 0 -> 0 [state SRC_TRYWAIT, polarity 0, disconnected]
> [  447.280926] CC1: 0 -> 2, CC2: 0 -> 0 [state SRC_TRYWAIT, polarity 0, connected]
> [  447.280970] state change SRC_TRYWAIT -> SRC_TRYWAIT
> [  447.281158] cc:=3
> [  447.307767] pending state change SRC_TRYWAIT -> SRC_ATTACHED @ 200 ms
> [  447.307838] CC1: 2 -> 0, CC2: 0 -> 0 [state SRC_TRYWAIT, polarity 0, disconnected]
> [  447.307858] state change SRC_TRYWAIT -> SRC_TRYWAIT
> 
> In TCPM, tDRPTry is set tp 100ms (min 75ms and max 150ms)
> and tCCdebounce is set to 200ms (min 100ms and max 200ms).
> To overcome the issue, record the time at which the port
> enters TryWait.SRC(SRC_TRYWAIT) and re-enter SRC_TRYWAIT
> only when CC keeps debouncing within tDRPTry.
> 
> Signed-off-by: Badhri Jagan Sridharan <Badhri@xxxxxxxxxx>

Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>

> ---
>  drivers/staging/typec/tcpm.c | 45 ++++++++++++++++++++++++++++----------------
>  1 file changed, 29 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/staging/typec/tcpm.c b/drivers/staging/typec/tcpm.c
> index 1219e3bc13ef..d45ffa8f2cfd 100644
> --- a/drivers/staging/typec/tcpm.c
> +++ b/drivers/staging/typec/tcpm.c
> @@ -17,6 +17,7 @@
>  #include <linux/completion.h>
>  #include <linux/debugfs.h>
>  #include <linux/device.h>
> +#include <linux/jiffies.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
> @@ -105,6 +106,7 @@
>  	S(SNK_TRY),				\
>  	S(SNK_TRY_WAIT),			\
>  	S(SRC_TRYWAIT),				\
> +	S(SRC_TRYWAIT_DEBOUNCE),		\
>  	S(SRC_TRYWAIT_UNATTACHED),		\
>  						\
>  	S(SRC_TRY),				\
> @@ -284,6 +286,9 @@ struct tcpm_port {
>  	struct typec_altmode *partner_altmode[SVID_DISCOVERY_MAX];
>  	struct typec_altmode *port_altmode[SVID_DISCOVERY_MAX];
>  
> +	/* Deadline in jiffies to exit src_try_wait state */
> +	unsigned long max_wait;
> +
>  #ifdef CONFIG_DEBUG_FS
>  	struct dentry *dentry;
>  	struct mutex logbuffer_lock;	/* log buffer access lock */
> @@ -2204,6 +2209,7 @@ static void run_state_machine(struct tcpm_port *port)
>  		if (!tcpm_port_is_sink(port)) {
>  			tcpm_set_state(port, SRC_TRYWAIT,
>  				       PD_T_PD_DEBOUNCE);
> +			port->max_wait = 0;
>  			break;
>  		}
>  		/* No vbus, cc state is sink or open */
> @@ -2211,11 +2217,22 @@ static void run_state_machine(struct tcpm_port *port)
>  		break;
>  	case SRC_TRYWAIT:
>  		tcpm_set_cc(port, tcpm_rp_cc(port));
> -		if (!port->vbus_present && tcpm_port_is_source(port))
> -			tcpm_set_state(port, SRC_ATTACHED, PD_T_CC_DEBOUNCE);
> -		else
> +		if (port->max_wait == 0) {
> +			port->max_wait = jiffies +
> +					 msecs_to_jiffies(PD_T_DRP_TRY);
>  			tcpm_set_state(port, SRC_TRYWAIT_UNATTACHED,
>  				       PD_T_DRP_TRY);
> +		} else {
> +			if (time_is_after_jiffies(port->max_wait))
> +				tcpm_set_state(port, SRC_TRYWAIT_UNATTACHED,
> +					       jiffies_to_msecs(port->max_wait -
> +								jiffies));
> +			else
> +				tcpm_set_state(port, SNK_UNATTACHED, 0);
> +		}
> +		break;
> +	case SRC_TRYWAIT_DEBOUNCE:
> +		tcpm_set_state(port, SRC_ATTACHED, PD_T_CC_DEBOUNCE);
>  		break;
>  	case SRC_TRYWAIT_UNATTACHED:
>  		tcpm_set_state(port, SNK_UNATTACHED, 0);
> @@ -2898,11 +2915,10 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
>  	case SRC_TRYWAIT:
>  		/* Hand over to state machine if needed */
>  		if (!port->vbus_present && tcpm_port_is_source(port))
> -			new_state = SRC_ATTACHED;
> -		else
> -			new_state = SRC_TRYWAIT_UNATTACHED;
> -
> -		if (new_state != port->delayed_state)
> +			tcpm_set_state(port, SRC_TRYWAIT_DEBOUNCE, 0);
> +		break;
> +	case SRC_TRYWAIT_DEBOUNCE:
> +		if (port->vbus_present || !tcpm_port_is_source(port))
>  			tcpm_set_state(port, SRC_TRYWAIT, 0);
>  		break;
>  	case SNK_TRY_WAIT:
> @@ -2990,9 +3006,10 @@ static void _tcpm_pd_vbus_on(struct tcpm_port *port)
>  		/* Do nothing, waiting for timeout */
>  		break;
>  	case SRC_TRYWAIT:
> -		/* Hand over to state machine if needed */
> -		if (port->delayed_state != SRC_TRYWAIT_UNATTACHED)
> -			tcpm_set_state(port, SRC_TRYWAIT, 0);
> +		/* Do nothing, Waiting for Rd to be detected */
> +		break;
> +	case SRC_TRYWAIT_DEBOUNCE:
> +		tcpm_set_state(port, SRC_TRYWAIT, 0);
>  		break;
>  	case SNK_TRY_WAIT:
>  		if (tcpm_port_is_sink(port)) {
> @@ -3039,11 +3056,7 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
>  	case SRC_TRYWAIT:
>  		/* Hand over to state machine if needed */
>  		if (tcpm_port_is_source(port))
> -			new_state = SRC_ATTACHED;
> -		else
> -			new_state = SRC_TRYWAIT_UNATTACHED;
> -		if (new_state != port->delayed_state)
> -			tcpm_set_state(port, SRC_TRYWAIT, 0);
> +			tcpm_set_state(port, SRC_TRYWAIT_DEBOUNCE, 0);
>  		break;
>  	case SNK_TRY_WAIT:
>  		if (!tcpm_port_is_sink(port))
> -- 
> 2.14.1.342.g6490525c54-goog
>