On Thu, May 23, 2024 at 07:17:52PM +0200, Sebastian Reichel wrote:
> When the Linux Type-C controller drivers probe, they requests a soft
> reset, which should result in the source restarting to send Source
> Capability messages again independently of the previous state.
> Unfortunately some USB PD sources do not follow the specification and
> do not send them after a soft reset when they already negotiated a
> specific contract before. The current way (and what is described in the
> specificiation) to resolve this problem is triggering a hard reset.
>
> But a hard reset is fatal on batteryless platforms powered via USB-C PD,
> since that removes VBUS for some time. Since this is triggered at boot
> time, the system will be stuck in a boot loop. Examples for platforms
> affected by this are the Radxa Rock 5B or the Libre Computer Renegade
> Elite ROC-RK3399-PC.
>
> Instead of directly trying a hard reset when no Source Capability
> message is send by the USB-PD source automatically, this changes the
> state machine to try explicitly asking for the capabilities by sending
> a Get Source Capability control message.
>
> For me this solves issues with 2 different USB-PD sources - a RAVPower
> powerbank and a Lemorele USB-C dock. Every other PD source I own
> follows the specification and automatically sends the Source Capability
> message after a soft reset, which works with or without this change.
>
> I decided against making this extra step limited to devices not having
> the self_powered flag set, since I don't see any huge drawbacks in this
> approach and it keeps the logic simpler. The worst case scenario would
> be a power source, which is really stuck. In that case the hard reset
> is delayed by another 310ms.
>
> Signed-off-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
Acked-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> ---
> drivers/usb/typec/tcpm/tcpm.c | 27 +++++++++++++++++++++++++--
> 1 file changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 375bc84d14a2..bac6866617c8 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -57,6 +57,7 @@
> S(SNK_DISCOVERY_DEBOUNCE), \
> S(SNK_DISCOVERY_DEBOUNCE_DONE), \
> S(SNK_WAIT_CAPABILITIES), \
> + S(SNK_WAIT_CAPABILITIES_TIMEOUT), \
> S(SNK_NEGOTIATE_CAPABILITIES), \
> S(SNK_NEGOTIATE_PPS_CAPABILITIES), \
> S(SNK_TRANSITION_SINK), \
> @@ -3108,7 +3109,8 @@ static void tcpm_pd_data_request(struct tcpm_port *port,
> PD_MSG_CTRL_REJECT :
> PD_MSG_CTRL_NOT_SUPP,
> NONE_AMS);
> - } else if (port->state == SNK_WAIT_CAPABILITIES) {
> + } else if (port->state == SNK_WAIT_CAPABILITIES ||
> + port->state == SNK_WAIT_CAPABILITIES_TIMEOUT) {
> /*
> * This message may be received even if VBUS is not
> * present. This is quite unexpected; see USB PD
> @@ -5039,10 +5041,31 @@ static void run_state_machine(struct tcpm_port *port)
> tcpm_set_state(port, SNK_SOFT_RESET,
> PD_T_SINK_WAIT_CAP);
> } else {
> - tcpm_set_state(port, hard_reset_state(port),
> + tcpm_set_state(port, SNK_WAIT_CAPABILITIES_TIMEOUT,
> PD_T_SINK_WAIT_CAP);
> }
> break;
> + case SNK_WAIT_CAPABILITIES_TIMEOUT:
> + /*
> + * There are some USB PD sources in the field, which do not
> + * properly implement the specification and fail to start
> + * sending Source Capability messages after a soft reset. The
> + * specification suggests to do a hard reset when no Source
> + * capability message is received within PD_T_SINK_WAIT_CAP,
> + * but that might effectively kil the machine's power source.
> + *
> + * This slightly diverges from the specification and tries to
> + * recover from this by explicitly asking for the capabilities
> + * using the Get_Source_Cap control message before falling back
> + * to a hard reset. The control message should also be supported
> + * and handled by all USB PD source and dual role devices
> + * according to the specification.
> + */
> + if (tcpm_pd_send_control(port, PD_CTRL_GET_SOURCE_CAP, TCPC_TX_SOP))
> + tcpm_set_state_cond(port, hard_reset_state(port), 0);
> + else
> + tcpm_set_state(port, hard_reset_state(port), PD_T_SINK_WAIT_CAP);
> + break;
> case SNK_NEGOTIATE_CAPABILITIES:
> port->pd_capable = true;
> tcpm_set_partner_usb_comm_capable(port,
> --
> 2.43.0
--
heikki
