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Message-ID: <20201201131552.GB232197@roeck-us.net>
Date: Tue, 1 Dec 2020 05:15:52 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Badhri Jagan Sridharan <badhri@...gle.com>
Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/3] usb: typec: tcpm: Introduce vsafe0v for vbus
On Mon, Nov 30, 2020 at 05:32:44PM -0800, Badhri Jagan Sridharan wrote:
> TCPM at present lacks the notion of VSAFE0V. There
> are three vbus threshold levels that are critical to track:
> a. vSafe5V - VBUS “5 volts” as defined by the USB
> PD specification.
> b. vSinkDisconnect - Threshold used for transition from
> Attached.SNK to Unattached.SNK.
> c. vSafe0V - VBUS “0 volts” as defined by the USB
> PD specification.
>
> Tracking vSafe0V is crucial for entry into Try.SNK and
> Attached.SRC and turning vbus back on by the source in
> response to hard reset.
>
> From "4.5.2.2.8.2 Exiting from AttachWait.SRC State" section
> in the Type-C spec:
>
> "The port shall transition to Attached.SRC when VBUS is at
> vSafe0V and the SRC.Rd state is detected on exactly one of
> the CC1 or CC2 pins for at least tCCDebounce."
>
> "A DRP that strongly prefers the Sink role may optionally
> transition to Try.SNK instead of Attached.SRC when VBUS
> is at vSafe0V and the SRC.Rd state is detected on exactly
> one of the CC1 or CC2 pins for at least tCCDebounce."
>
> From "7.1.5 Response to Hard Resets" section in the PD spec:
>
> "After establishing the vSafe0V voltage condition on VBUS,
> the Source Shall wait tSrcRecover before re-applying VCONN
> and restoring VBUS to vSafe5V."
>
> vbus_present in the TCPM code tracks vSafe5V(vbus_present is true)
> and vSinkDisconnect(vbus_present is false).
>
> This change adds is_vbus_vsafe0v callback which when set makes
> TCPM query for vSafe0V voltage level when needed.
>
> Since not all TCPC controllers might have the capability
> to report vSafe0V, TCPM assumes that vSafe0V is same as
> vSinkDisconnect when is_vbus_vsafe0v callback is not set.
> This allows TCPM to continue to support controllers which don't
> have the support for reporting vSafe0V.
>
> Introducing vSafe0V helps fix the failure reported at
> "Step 15. CVS verifies PUT remains in AttachWait.SRC for 500ms"
> of "TD 4.7.2 Try. SNK DRP Connect DRP Test" of
> "Universal Serial Bus Type-C (USB Type-C) Functional Test
> Specification Chapters 4 and 5". Here the compliance tester
> intentionally maintains vbus at greater than vSafe0V and expects
> the Product under test to stay in AttachWait.SRC till vbus drops
> to vSafe0V.
>
> Signed-off-by: Badhri Jagan Sridharan <badhri@...gle.com>
> ---
> drivers/usb/typec/tcpm/tcpm.c | 63 +++++++++++++++++++++++++++++------
> include/linux/usb/tcpm.h | 6 ++++
> 2 files changed, 58 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 3bbc1f10af49..10a065eef73e 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -258,7 +258,19 @@ struct tcpm_port {
> bool attached;
> bool connected;
> enum typec_port_type port_type;
> +
> + /*
> + * Set to true when vbus is greater than VSAFE5V min.
> + * Set to false when vbus falls below vSinkDisconnect max threshold.
> + */
> bool vbus_present;
> +
> + /*
> + * Set to true when vbus is less than VSAFE0V max.
> + * Set to false when vbus is greater than VSAFE0V max.
> + */
> + bool vbus_vsafe0v;
> +
> bool vbus_never_low;
> bool vbus_source;
> bool vbus_charge;
> @@ -3094,7 +3106,7 @@ static void run_state_machine(struct tcpm_port *port)
> else if (tcpm_port_is_audio(port))
> tcpm_set_state(port, AUDIO_ACC_ATTACHED,
> PD_T_CC_DEBOUNCE);
> - else if (tcpm_port_is_source(port))
> + else if (tcpm_port_is_source(port) && port->vbus_vsafe0v)
> tcpm_set_state(port,
> tcpm_try_snk(port) ? SNK_TRY
> : SRC_ATTACHED,
> @@ -4097,6 +4109,12 @@ static void _tcpm_pd_vbus_on(struct tcpm_port *port)
> {
> tcpm_log_force(port, "VBUS on");
> port->vbus_present = true;
> + /*
> + * When vbus_present is true i.e. Voltage at VBUS is greater than VSAFE5V implicitly
> + * states that vbus is not at VSAFE0V, hence clear the vbus_vsafe0v flag here.
> + */
> + port->vbus_vsafe0v = false;
> +
> switch (port->state) {
> case SNK_TRANSITION_SINK_VBUS:
> port->explicit_contract = true;
> @@ -4186,16 +4204,8 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
> case SNK_HARD_RESET_SINK_OFF:
> tcpm_set_state(port, SNK_HARD_RESET_WAIT_VBUS, 0);
> break;
> - case SRC_HARD_RESET_VBUS_OFF:
> - /*
> - * After establishing the vSafe0V voltage condition on VBUS, the Source Shall wait
> - * tSrcRecover before re-applying VCONN and restoring VBUS to vSafe5V.
> - */
> - tcpm_set_state(port, SRC_HARD_RESET_VBUS_ON, PD_T_SRC_RECOVER);
> - break;
> case HARD_RESET_SEND:
> break;
> -
> case SNK_TRY:
> /* Do nothing, waiting for timeout */
> break;
> @@ -4266,6 +4276,28 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
> }
> }
>
> +static void _tcpm_pd_vbus_vsafe0v(struct tcpm_port *port)
> +{
> + tcpm_log_force(port, "VBUS VSAFE0V");
> + port->vbus_vsafe0v = true;
> + switch (port->state) {
> + case SRC_HARD_RESET_VBUS_OFF:
> + /*
> + * After establishing the vSafe0V voltage condition on VBUS, the Source Shall wait
> + * tSrcRecover before re-applying VCONN and restoring VBUS to vSafe5V.
> + */
> + tcpm_set_state(port, SRC_HARD_RESET_VBUS_ON, PD_T_SRC_RECOVER);
> + break;
> + case SRC_ATTACH_WAIT:
> + if (tcpm_port_is_source(port))
> + tcpm_set_state(port, tcpm_try_snk(port) ? SNK_TRY : SRC_ATTACHED,
> + PD_T_CC_DEBOUNCE);
> + break;
> + default:
> + break;
> + }
> +}
> +
> static void _tcpm_pd_hard_reset(struct tcpm_port *port)
> {
> tcpm_log_force(port, "Received hard reset");
> @@ -4301,10 +4333,19 @@ static void tcpm_pd_event_handler(struct kthread_work *work)
> bool vbus;
>
> vbus = port->tcpc->get_vbus(port->tcpc);
> - if (vbus)
> + if (vbus) {
> _tcpm_pd_vbus_on(port);
> - else
> + } else {
> _tcpm_pd_vbus_off(port);
> + /*
> + * When TCPC does not support detecting vsafe0v voltage level,
> + * treat vbus absent as vsafe0v. Else invoke is_vbus_vsafe0v
> + * to see if vbus has discharge to VSAFE0V.
> + */
> + if (!port->tcpc->is_vbus_vsafe0v ||
> + port->tcpc->is_vbus_vsafe0v(port->tcpc) > 0)
> + _tcpm_pd_vbus_vsafe0v(port);
> + }
> }
> if (events & TCPM_CC_EVENT) {
> enum typec_cc_status cc1, cc2;
> diff --git a/include/linux/usb/tcpm.h b/include/linux/usb/tcpm.h
> index e68aaa12886f..615d4532c028 100644
> --- a/include/linux/usb/tcpm.h
> +++ b/include/linux/usb/tcpm.h
> @@ -98,6 +98,11 @@ enum tcpm_transmit_type {
> * will be turned on. requested_vbus_voltage is set to 0 when vbus
> * is going to disappear knowingly i.e. during PR_SWAP and
> * HARD_RESET etc.
> + * @is_vbus_vsafe0v:
> + * Optional; TCPCI spec based TCPC implementations are expected to
> + * detect VSAFE0V voltage level at vbus. When detection of VSAFE0V
> + * is supported by TCPC, set this callback for TCPM to query
> + * whether vbus is at VSAFE0V when needed.
Return values ?
> */
> struct tcpc_dev {
> struct fwnode_handle *fwnode;
> @@ -128,6 +133,7 @@ struct tcpc_dev {
> int (*enable_auto_vbus_discharge)(struct tcpc_dev *dev, bool enable);
> int (*set_auto_vbus_discharge_threshold)(struct tcpc_dev *dev, enum typec_pwr_opmode mode,
> bool pps_active, u32 requested_vbus_voltage);
> + int (*is_vbus_vsafe0v)(struct tcpc_dev *dev);
I don't really see the point of returning an int here. If an error is
returned, it should be checked. However, that is not currently the case;
an error is treated as "false" return. As such, the function may as well
return true/false (and false if an error is observed).
> };
>
> struct tcpm_port;
> --
> 2.29.2.454.gaff20da3a2-goog
>
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