Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers

From	Heikki Krogerus <heikki.krogerus@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
Date	2017-05-19 12:40 +0200
Message-ID	<tINu9-QO-7@gated-at.bofh.it> (permalink)
References	(1 earlier) <tI1IS-8F-5@gated-at.bofh.it> <tI3AZ-1j2-3@gated-at.bofh.it> <tIpLc-8ip-13@gated-at.bofh.it> <tIwWm-5mj-9@gated-at.bofh.it> <tIAQh-r6-5@gated-at.bofh.it>
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On Thu, May 18, 2017 at 02:08:53PM -0700, Badhri Jagan Sridharan wrote:
> On Thu, May 18, 2017 at 9:51 AM, Guenter Roeck <linux@roeck-us.net> wrote:
> > On Thu, May 18, 2017 at 11:13:51AM +0200, Oliver Neukum wrote:
> >> Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck:
> >> > On 05/17/2017 12:34 AM, Oliver Neukum wrote:
> >> > >
> >> > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan
> >> > > Sridharan:
> >> > >
> >> > > Hi,
> >> > >
> >> > > >
> >> > > > "Two independent set of mechanisms are defined to allow a USB Type-C
> >> > > > DRP to functionally swap power and data roles. When USB PD is
> >> > > > supported, power and data role swapping is performed as a subsequent
> >> > > > step following the initial connection process. For non-PD implementations,
> >> > > > power/data role swapping can optionally be dealt with as part of the initial
> >> > > > connection process."
> >> > >
> >> > > Well, as I read it, without PD once a connection is established, you
> >> > > are stuck with your role. So it seems to me that blocking a later
> >> > > attempt to change it makes sense.
> >> > >
> >> >
> >> > That seems to be a harsh and not very user friendly reading of the specification.
> >> >
> >> > I would argue that the user doesn't care if the partner supports PD or not
> >> > when selecting a role, and I would prefer to provide an implementation which is
> >> > as user friendly as possible.
> >>
> >> Data role, no question, you are right.
> >> Power role is a different question. A switch of power role with PD should
> >> not lead to a disconnect. Any other method might. So equating them does
> >> not look like a good idea.
> >>
> >
> > Not really sure I can follow. If a partner does not support PD, there is no
> > real distinction between data role and power role, or am I missing something ?
> >
> > Are you saying that, if a partner does not support PD, user space should
> > request a data role swap instead, and that this would be acceptable for you ?
> >
> > I don't really understand the difference - a data role swap doesn't cause
> > a disconnect either if the partner supports PD, and it would still result
> > in a disconnect/reconnect sequence if the partner does not support PD -
> > but if it works for you, fine with me.
> >
> > Badhri, would that work for us ?
> 
> Yes Geunter that should work as well. Requesting non-pd role swap either through
> current_power_role or current_data_role is virtually the same.

So if I understood this correctly, we'll skip this change, right?


Thanks,

-- 
heikki

Thread

[PATCH] usb: typec: Defer checking of valid power role swap to low level drivers Badhri Jagan Sridharan <badhri@google.com> - 2017-05-17 09:40 +0200
  Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Oliver Neukum <oneukum@suse.com> - 2017-05-17 09:40 +0200
    Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Guenter Roeck <linux@roeck-us.net> - 2017-05-17 11:40 +0200
      Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Heikki Krogerus <heikki.krogerus@linux.intel.com> - 2017-05-17 14:40 +0200
        Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Guenter Roeck <linux@roeck-us.net> - 2017-05-17 15:10 +0200
          Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Heikki Krogerus <heikki.krogerus@linux.intel.com> - 2017-05-17 16:00 +0200
            Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Badhri Jagan Sridharan <badhri@google.com> - 2017-05-17 20:10 +0200
      Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Oliver Neukum <oneukum@suse.com> - 2017-05-18 11:20 +0200
        Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Guenter Roeck <linux@roeck-us.net> - 2017-05-18 19:00 +0200
          Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Badhri Jagan Sridharan <badhri@google.com> - 2017-05-18 23:10 +0200
            Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Badhri Jagan Sridharan <badhri@google.com> - 2017-05-18 23:20 +0200
            Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Heikki Krogerus <heikki.krogerus@linux.intel.com> - 2017-05-19 12:40 +0200
              Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Guenter Roeck <linux@roeck-us.net> - 2017-05-19 15:30 +0200
            Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Oliver Neukum <oneukum@suse.com> - 2017-05-19 12:50 +0200
  Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-05-17 10:10 +0200
    Re: [PATCH] usb: typec: Defer checking of valid power role swap to  low level drivers Guenter Roeck <linux@roeck-us.net> - 2017-05-17 11:50 +0200

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