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

From	Guenter Roeck <linux@roeck-us.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
Date	2017-05-19 15:30 +0200
Message-ID	<tIQ8F-2Jx-9@gated-at.bofh.it> (permalink)
References	(2 earlier) <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> <tINu9-QO-7@gated-at.bofh.it>
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On 05/19/2017 03:35 AM, Heikki Krogerus wrote:
> 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?
> 
Yes.

Thanks,
Guenter

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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