linux-kernel - Re: [PATCH 1/2] typec: tcpm: Do not disconnect link for self powered devices

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Date:   Thu, 13 Sep 2018 16:24:08 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Badhri Jagan Sridharan <badhri@...gle.com>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [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@...gle.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