Re: [PATCH v2] usb: typec: tcpm: Wait for vbus discharge to VSAFE0V before toggling
From: Badhri Jagan Sridharan
Date: Thu Feb 25 2021 - 00:47:47 EST
On Fri, Feb 19, 2021 at 7:56 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
>
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@xxxxxxxxxx>
>
> ---
>
> 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);
>
Yes this should be OK as well. I was thinking it would be more
clearer during debug if there
was a separate state altogether, but, looks like we should be fine.
Implementing/Validating it now. Will send a follow up version today.
>
In this context, any idea why port_type==TYPEC_PORT_DRP results in
>
SNK_UNATTACHED state ? That seems a bit odd.
This comes from the patch here:
https://lore.kernel.org/r/1582128343-22438-1-git-send-email-jun.li@xxxxxxx
Looks reasonable to me as tcpm_*_detach functions call tcpm_detach so
teardown should
happen anyways.
static void tcpm_snk_detach(struct tcpm_port *port)
{
tcpm_detach(port);
}
static void tcpm_src_detach(struct tcpm_port *port)
{
tcpm_detach(port);
}
Thanks,
Badhri
>
>
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;
>
> }
>
>
>