Re: [PATCH] usb: typec: tcpm: always rediscover when swapping DR

[Kyle Tso]

On Wed, Aug 18, 2021 at 5:27 PM Icenowy Zheng <icenowy@xxxxxxx> wrote:
>
>
>
> 于 2021年8月18日 GMT+08:00 下午4:02:24, Kyle Tso <kyletso@xxxxxxxxxx> 写到:
> >On Tue, Aug 17, 2021 at 11:13 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> >>
> >> On 8/17/21 2:36 AM, Heikki Krogerus wrote:
> >> > On Fri, Aug 13, 2021 at 12:31:31PM +0800, Icenowy Zheng wrote:
> >> >> Currently, TCPM code omits discover when swapping to gadget, and assume
> >> >> that no altmodes are available when swapping from gadget. However, we do
> >> >> send discover when we get attached as gadget -- this leads to modes to be
> >> >> discovered twice when attached as gadget and then swap to host.
> >> >>
> >> >> Always re-send discover when swapping DR, regardless of what change is
> >> >> being made; and because of this, the assumption that no altmodes are
> >> >> registered with gadget role is broken, and altmodes de-registeration is
> >> >> always needed now.
> >> >>
> >> >> Signed-off-by: Icenowy Zheng <icenowy@xxxxxxx>
> >> >> ---
> >> >>   drivers/usb/typec/tcpm/tcpm.c | 9 ++++-----
> >> >>   1 file changed, 4 insertions(+), 5 deletions(-)
> >> >>
> >> >> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> >> >> index b9bb63d749ec..ab6d0d51ee1c 100644
> >> >> --- a/drivers/usb/typec/tcpm/tcpm.c
> >> >> +++ b/drivers/usb/typec/tcpm/tcpm.c
> >> >> @@ -4495,15 +4495,14 @@ static void run_state_machine(struct tcpm_port *port)
> >> >>              tcpm_set_state(port, ready_state(port), 0);
> >> >>              break;
> >> >>      case DR_SWAP_CHANGE_DR:
> >> >> -            if (port->data_role == TYPEC_HOST) {
> >> >> -                    tcpm_unregister_altmodes(port);
> >> >> +            tcpm_unregister_altmodes(port);
> >> >> +            if (port->data_role == TYPEC_HOST)
> >> >>                      tcpm_set_roles(port, true, port->pwr_role,
> >> >>                                     TYPEC_DEVICE);
> >> >> -            } else {
> >> >> +            else
> >> >>                      tcpm_set_roles(port, true, port->pwr_role,
> >> >>                                     TYPEC_HOST);
> >> >> -                    port->send_discover = true;
> >> >> -            }
> >> >> +            port->send_discover = true;
> >> >>              tcpm_ams_finish(port);
> >> >>              tcpm_set_state(port, ready_state(port), 0);
> >> >>              break;
> >> >
> >> > Why is it necessary to do discovery with data role swap in general?
> >> >
> >> > thanks,
> >> >
> >>
> >> Additional question: There are two patches pending related to DR_SWAP
> >> and discovery. Are they both needed, or do they both solve the same
> >> problem ?
> >>
> >> Thanks,
> >> Guenter
> >
> >Hi, I just noticed this patch.
> >
> >Part of this patch and part of my patch
> >https://lore.kernel.org/r/20210816075449.2236547-1-kyletso@xxxxxxxxxx
> >are to solve the same problem that Discover_Identity is not sent in a
> >case where the port becomes UFP after DR_SWAP while in PD3.
> >
> >The difference (for the DR_SWAP part) is that my patch does not set
> >the flag "send_discover" if the port becomes UFP after PD2 DR_SWAP.
> >That is because in PD2 Spec, UFP is not allowed to be the SVDM
> >Initiator.
> >
> >This patch indeed solves another problem where
> >tcpm_unregister_altmodes should be called during PD3 DR_SWAP because
> >the port partner may return mode data in the latest Discover_Mode. For
> >the PD2 case, I don't think it needs to be called because PD2 DFP will
> >always return NAK for Discover_Mode. However it is fine because it is
>
> It sounds like my dock is doing something against the specification...
>
> It sends altmodes rather than NAK when my board gets attached as
> UFP and send bogus discovers (because of bugs of current TCPM
> code). These altmodes are then registered in TCPM and never get
> cleaned up within it, which leads to conflict when the dock is
> removed and then re-inserted.
>

Could you provide more details?
1. Is the connection in PD3 ?
2. Could you provide the tcpm logs?

> (BTW is it neceesary for data role and power role to be the same
> when attaching? My board now gets attached as UFP to drain
> power, and then do DR_SWAP to become USB host.)
>

Either Sink/UFP or Source/DFP in the beginning. Then DR_SWAP is okay
when both ports are in ready state. Your dock looks like a Sourcing
Device.

Type-C Spec:
```
4.8.4 Sourcing Device

A Sourcing Device is a special sub-class of a DRP that is capable of
supplying power, but is not capable of acting as a USB host. For
example a hub’s UFP or a monitor’s UFP that operates as a device but
not as a host.

The Sourcing Device shall follow the rules for a DRP (See Section
4.5.1.4 and Figure 4-15). It shall also follow the requirements for
the Source as Power Source (See Section 4.8.1). The Sourcing Device
shall support USB PD and shall support the DR_Swap command in order to
enable the Source to assume the UFP data role.
```

thanks,
Kyle

> >safe to call tcpm_unregister_altmodes even if there is no mode data.
> >
> >In fact, when I was tracing the code I found another bug. PD2 UFP is
> >not allowed to send Discover_Identity and Discover_Mode. I can send
> >another patch to address this problem.
> >
> >thanks,
> >Kyle