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SubjectRe: [PATCH 1/2] typec: tcpm: Do not disconnect link for self powered devices
+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);
>
> /*
> * 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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