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SubjectRe: [PATCH 1/2] typec: tcpm: Do not disconnect link for self powered devices
On Thu, Sep 13, 2018 at 04:24:08PM +0300, Heikki Krogerus wrote:
> +Guenter
>
> On Wed, Sep 12, 2018 at 07:11:12PM -0700, Badhri Jagan Sridharan wrote:
> > During HARD_RESET the data link is disconnected.
> > For self powered device, the spec is advising against doing that.
> >
> > >From USB_PD_R3_0
> > 7.1.5 Response to Hard Resets
> > Device operation during and after a Hard Reset is defined as follows:
> > Self-powered devices Should Not disconnect from USB during a Hard Reset
> > (see Section 9.1.2).
> > Bus powered devices will disconnect from USB during a Hard Reset due to the
> > loss of their power source.
> >
> > Tackle this by letting TCPM know whether the device is self or bus powered.
> >
> > This overcomes unnecessary port disconnections from hard reset.
> > Also, speeds up the enumeration time when connected to Type-A ports.
> >
> > Signed-off-by: Badhri Jagan Sridharan <Badhri@google.com>
> > ---
> > drivers/usb/typec/tcpm.c | 6 +++++-
> > include/linux/usb/tcpm.h | 1 +
> > 2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
> > index 4f1f4215f3d6..a4e0c027a2a9 100644
> > --- a/drivers/usb/typec/tcpm.c
> > +++ b/drivers/usb/typec/tcpm.c
> > @@ -3270,7 +3270,11 @@ static void run_state_machine(struct tcpm_port *port)
> > memset(&port->pps_data, 0, sizeof(port->pps_data));
> > tcpm_set_vconn(port, false);
> > tcpm_set_charge(port, false);
> > - tcpm_set_roles(port, false, TYPEC_SINK, TYPEC_DEVICE);
> > +
> > + if (port->tcpc->config->self_powered)
>
> Add a member for that flag to the struct tcpm_port, and check that
> here instead. I'll explain why below.
>
> > + tcpm_set_roles(port, true, TYPEC_SINK, TYPEC_DEVICE);
> > + else
> > + tcpm_set_roles(port, false, TYPEC_SINK, TYPEC_DEVICE);
> >

Maybe I am missing something, but
tcpm_set_roles(port, port->self_powered,
TYPEC_SINK, TYPEC_DEVICE);
should accomplish the same (assuming the flag is moved to tcpm_port).

Does the code at SRC_HARD_RESET_VBUS_OFF: also have to be changed,
or only SNK_HARD_RESET_SINK_OFF: ? In other words, does this only
apply if the port is a sink, or also if is is source ?

Guenter

> > /*
> > * VBUS may or may not toggle, depending on the adapter.
> > * If it doesn't toggle, transition to SNK_HARD_RESET_SINK_ON
> > diff --git a/include/linux/usb/tcpm.h b/include/linux/usb/tcpm.h
> > index 7e7fbfb84e8e..50c74a77db55 100644
> > --- a/include/linux/usb/tcpm.h
> > +++ b/include/linux/usb/tcpm.h
> > @@ -89,6 +89,7 @@ struct tcpc_config {
> > enum typec_port_data data;
> > enum typec_role default_role;
> > bool try_role_hw; /* try.{src,snk} implemented in hardware */
> > + bool self_powered; /* port belongs to a self powered device */
>
> I'm not sure we should add any more members to that structure, but
> maybe it's not a problem for now. We can't quite yet get rid of that
> structure.
>
> You do need to introduce a new device property already. Then read the
> value for that new member you added to struct tcpm_port in
> tcpm_fw_get_caps() and in tcpm_copy_caps().
>
>
> Thanks,
>
> --
> heikki

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