On Fri, Mar 15, 2019 at 03:42:19PM +0100, Hans de Goede wrote:
> PD 2.0 sinks are supposed to accept src-capabilities with a 3.0 header and
> simply ignore any src PDOs which the sink does not understand such as PPS
> but some 2.0 sinks instead ignore the entire PD_DATA_SOURCE_CAP message,
> causing contract negotiation to fail.
>
> This commit fixes such sinks not working by re-trying the contract
> negotiation with PD-2.0 source-caps messages if we don't have a contract
> after PD_N_HARD_RESET_COUNT hard-reset attempts.
>
> The problem fixed by this commit was noticed with a Type-C to VGA dongle.
>
> Signed-off-by: Hans de Goede <hdego...@redhat.com>
> ---
> The Type-C to VGA dongle on which this encountered looks like this one:
> https://www.aliexpress.com/item/Male-USB-3-1-Type-C-USB-C-to-Female-VGA-Adapter-Cable-10Gbps-for-New/32898274476.html
> ---
> drivers/usb/typec/tcpm/tcpm.c | 34 +++++++++++++++++++++++++++++++++-
> 1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index f1c39a3c7534..3f8df845d1a5 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -37,6 +37,7 @@
> S(SRC_ATTACHED), \
> S(SRC_STARTUP), \
> S(SRC_SEND_CAPABILITIES), \
> + S(SRC_SEND_CAP_LOWER_PD_REVISION), \
> S(SRC_NEGOTIATE_CAPABILITIES), \
> S(SRC_TRANSITION_SUPPLY), \
> S(SRC_READY), \
> @@ -2792,6 +2793,29 @@ static inline enum tcpm_state hard_reset_state(struct
> tcpm_port *port)
> return SNK_UNATTACHED;
> }
>
> +/*
> + * PD 2.0 sinks are supposed to accept src-capabilities with a 3.0 header and
> + * simply ignore any src PDOs which the sink does not understand such as PPS
> + * but some 2.0 sinks instead ignore the entire PD_DATA_SOURCE_CAP message,
> + * causing contract negotiation to fail.
> + *
> + * This function is used by the SRC_SEND_CAPABILITIES state in
> + * run_state_machine() to work around this.
> + *
> + * After PD_N_HARD_RESET_COUNT hard-reset attempts this function selects
> + * SRC_SEND_CAP_LOWER_PD_REVISION as state to set after the next timeout,
> + * this state will fallback to a lower PD revision and then try sending the
> + * src-capabilities again.
> + */
> +static inline enum tcpm_state src_send_cap_timeout_state(struct tcpm_port
> *port)
> +{
> + if (port->hard_reset_count < PD_N_HARD_RESET_COUNT)
> + return HARD_RESET_SEND;
> + if (port->negotiated_rev > PD_REV20)
> + return SRC_SEND_CAP_LOWER_PD_REVISION;
> + return hard_reset_state(port);
> +}
> +
> static inline enum tcpm_state unattached_state(struct tcpm_port *port)
> {
> if (port->port_type == TYPEC_PORT_DRP) {
> @@ -2966,10 +2990,18 @@ static void run_state_machine(struct tcpm_port *port)
> /* port->hard_reset_count = 0; */
> port->caps_count = 0;
> port->pd_capable = true;
> - tcpm_set_state_cond(port, hard_reset_state(port),
> + tcpm_set_state_cond(port,
> + src_send_cap_timeout_state(port),
> PD_T_SEND_SOURCE_CAP);
> }
> break;
> + case SRC_SEND_CAP_LOWER_PD_REVISION:
> + if (WARN_ON(port->negotiated_rev <= PD_REV20))
> + break;
I really dislike the WARN_ON here. A bad remote can potentially trigger
this, which on systems with crash on warning enabled can result in a
reboot. Just revert to the original behavior here, and maybe add
a tcpm log message.
Guenter
> + port->negotiated_rev--;
> + port->hard_reset_count = 0;
> + tcpm_set_state(port, SRC_SEND_CAPABILITIES, 0);
> + break;
> case SRC_NEGOTIATE_CAPABILITIES:
> ret = tcpm_pd_check_request(port);
> if (ret < 0) {
> --
> 2.20.1
>
