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Message-ID: <20170827172127.GM22819@roeck-us.net>
Date: Sun, 27 Aug 2017 10:21:27 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Badhri Jagan Sridharan <badhri@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] staging: usb: tcpm: usb: typec: tcpm: Prevent TCPM
from looping in SRC_TRYWAIT
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@...gle.com>
Reviewed-by: Guenter Roeck <linux@...ck-us.net>
> ---
> 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
>
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