On Fri, Mar 15, 2019 at 05:43:05PM +0100, Hans de Goede wrote: > Hi, > > On 3/15/19 3:57 PM, Guenter Roeck wrote: > >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 <hdegoede@xxxxxxxxxx> > >>--- > >>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. > > How would a bad remote trigger this? > > We only ever call set_state with SRC_SEND_CAP_LOWER_PD_REVISION in the new > src_send_cap_timeout_state which has: > > if (port->negotiated_rev > PD_REV20) > return SRC_SEND_CAP_LOWER_PD_REVISION; > > So we really should never hit the WARN_ON, of we do hit the WARN_ON > something is seriously wrong. > If that situation can't happen, the check should not be there in the first place. Otherwise you could litter the implementation with WARN_ON all over the place, and make it all but unreadable. I am not in favor of code like that. Guenter > Regards, > > Hans > > > > > > >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 > >>
