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Date: Fri, 19 Feb 2021 07:56:37 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Badhri Jagan Sridharan <badhri@...gle.com>,
Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Kyle Tso <kyletso@...gle.com>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH v2] usb: typec: tcpm: Wait for vbus discharge to VSAFE0V
before toggling
On 2/19/21 1:04 AM, Badhri Jagan Sridharan wrote:
> When vbus auto discharge is enabled, TCPM can sometimes be faster than
> the TCPC i.e. TCPM can go ahead and move the port to unattached state
> (involves disabling vbus auto discharge) before TCPC could effectively
> discharge vbus to VSAFE0V. This leaves vbus with residual charge and
> increases the decay time which prevents tsafe0v from being met.
> This change introduces a new state VBUS_DISCHARGE where the TCPM waits
> for a maximum of tSafe0V(max) for vbus to discharge to VSAFE0V before
> transitioning to unattached state and re-enable toggling. If vbus
> discharges to vsafe0v sooner, then, transition to unattached state
> happens right away.
>
> Also, while in SNK_READY, when auto discharge is enabled, drive
> disconnect based on vbus turning off instead of Rp disappearing on
> CC pins. Rp disappearing on CC pins is almost instanteous compared
> to vbus decay.
>
> Fixes: f321a02caebd ("usb: typec: tcpm: Implement enabling Auto
> Discharge disconnect support")
> Signed-off-by: Badhri Jagan Sridharan <badhri@...gle.com>
> ---
> Changes since V1:
> - Add Fixes tag
> ---
> drivers/usb/typec/tcpm/tcpm.c | 60 +++++++++++++++++++++++++++++++----
> 1 file changed, 53 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index be0b6469dd3d..0ed71725980f 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -62,6 +62,8 @@
> S(SNK_TRANSITION_SINK_VBUS), \
> S(SNK_READY), \
> \
> + S(VBUS_DISCHARGE), \
> + \
> S(ACC_UNATTACHED), \
> S(DEBUG_ACC_ATTACHED), \
> S(AUDIO_ACC_ATTACHED), \
> @@ -438,6 +440,9 @@ struct tcpm_port {
> enum tcpm_ams next_ams;
> bool in_ams;
>
> + /* Auto vbus discharge state */
> + bool auto_vbus_discharge_enabled;
> +
> #ifdef CONFIG_DEBUG_FS
> struct dentry *dentry;
> struct mutex logbuffer_lock; /* log buffer access lock */
> @@ -3413,6 +3418,8 @@ static int tcpm_src_attach(struct tcpm_port *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);
> + if (!ret)
> + port->auto_vbus_discharge_enabled = true;
> }
>
> ret = tcpm_set_roles(port, true, TYPEC_SOURCE, tcpm_data_role_for_source(port));
> @@ -3495,6 +3502,8 @@ static void tcpm_reset_port(struct tcpm_port *port)
> 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);
> + if (!ret)
> + port->auto_vbus_discharge_enabled = false;
> }
> port->in_ams = false;
> port->ams = NONE_AMS;
> @@ -3568,6 +3577,8 @@ static int tcpm_snk_attach(struct tcpm_port *port)
> 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);
> + if (!ret)
> + port->auto_vbus_discharge_enabled = true;
> }
>
> ret = tcpm_set_roles(port, true, TYPEC_SINK, tcpm_data_role_for_sink(port));
> @@ -3684,6 +3695,12 @@ static void run_state_machine(struct tcpm_port *port)
> switch (port->state) {
> case TOGGLING:
> break;
> + case VBUS_DISCHARGE:
> + if (port->port_type == TYPEC_PORT_SRC)
> + tcpm_set_state(port, SRC_UNATTACHED, PD_T_SAFE_0V);
> + else
> + tcpm_set_state(port, SNK_UNATTACHED, PD_T_SAFE_0V);
> + break;
> /* SRC states */
> case SRC_UNATTACHED:
> if (!port->non_pd_role_swap)
> @@ -4669,7 +4686,9 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
> case SRC_READY:
> if (tcpm_port_is_disconnected(port) ||
> !tcpm_port_is_source(port)) {
> - if (port->port_type == TYPEC_PORT_SRC)
> + if (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v)
> + tcpm_set_state(port, VBUS_DISCHARGE, 0);
> + else if (port->port_type == TYPEC_PORT_SRC)
> tcpm_set_state(port, SRC_UNATTACHED, 0);
> else
> tcpm_set_state(port, SNK_UNATTACHED, 0);
Unless I am missing something, the new state is only used to set the
PD_T_SAFE_0V timeout. Is it really necessary/useful to add a new state
just for that, while keeping the rest of if/else statements ?
Personally I would prefer something like
timeout = (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v) ? PD_T_SAFE_0V : 0;
if (port->port_type == TYPEC_PORT_SRC)
tcpm_set_state(port, SRC_UNATTACHED, timeout);
else
tcpm_set_state(port, SNK_UNATTACHED, timeout);
In this context, any idea why port_type==TYPEC_PORT_DRP results in
SNK_UNATTACHED state ? That seems a bit odd.
Guenter
> @@ -4703,7 +4722,18 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
> tcpm_set_state(port, SNK_DEBOUNCED, 0);
> break;
> case SNK_READY:
> - if (tcpm_port_is_disconnected(port))
> + /*
> + * When set_auto_vbus_discharge_threshold is enabled, CC pins go
> + * away before vbus decays to disconnect threshold. Allow
> + * disconnect to be driven by vbus disconnect when auto vbus
> + * discharge is enabled.
> + *
> + * EXIT condition is based primarily on vbus disconnect and CC is secondary.
> + * "A port that has entered into USB PD communications with the Source and
> + * has seen the CC voltage exceed vRd-USB may monitor the CC pin to detect
> + * cable disconnect in addition to monitoring VBUS.
> + */
> + if (!port->auto_vbus_discharge_enabled && tcpm_port_is_disconnected(port))
> tcpm_set_state(port, unattached_state(port), 0);
> else if (!port->pd_capable &&
> (cc1 != old_cc1 || cc2 != old_cc2))
> @@ -4803,9 +4833,16 @@ static void _tcpm_cc_change(struct tcpm_port *port, enum typec_cc_status cc1,
> */
> break;
>
> + case VBUS_DISCHARGE:
> + /* Do nothing. Waiting for vsafe0v signal */
> + break;
> default:
> - if (tcpm_port_is_disconnected(port))
> - tcpm_set_state(port, unattached_state(port), 0);
> + if (tcpm_port_is_disconnected(port)) {
> + if (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v)
> + tcpm_set_state(port, VBUS_DISCHARGE, 0);
> + else
> + tcpm_set_state(port, unattached_state(port), 0);
> + }
> break;
> }
> }
> @@ -4988,9 +5025,12 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
> break;
>
> default:
> - if (port->pwr_role == TYPEC_SINK &&
> - port->attached)
> - tcpm_set_state(port, SNK_UNATTACHED, 0);
> + if (port->pwr_role == TYPEC_SINK && port->attached) {
> + if (port->auto_vbus_discharge_enabled && !port->vbus_vsafe0v)
> + tcpm_set_state(port, VBUS_DISCHARGE, 0);
> + else
> + tcpm_set_state(port, SNK_UNATTACHED, 0);
> + }
> break;
> }
> }
> @@ -5012,6 +5052,12 @@ static void _tcpm_pd_vbus_vsafe0v(struct tcpm_port *port)
> tcpm_set_state(port, tcpm_try_snk(port) ? SNK_TRY : SRC_ATTACHED,
> PD_T_CC_DEBOUNCE);
> break;
> + case VBUS_DISCHARGE:
> + if (port->port_type == TYPEC_PORT_SRC)
> + tcpm_set_state(port, SRC_UNATTACHED, 0);
> + else
> + tcpm_set_state(port, SNK_UNATTACHED, 0);
> + break;
> default:
> break;
> }
>
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