linux-kernel - Re: [PATCHv3 1/2] usb: USB Type-C connector class

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Message-ID: <57727B89.7040802@roeck-us.net>
Date:	Tue, 28 Jun 2016 06:28:41 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:	Rajaram R <rajaram.officemail@...il.com>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Oliver Neukum <oneukum@...e.com>
Subject: Re: [PATCHv3 1/2] usb: USB Type-C connector class

On 06/28/2016 06:12 AM, Heikki Krogerus wrote:
> On Mon, Jun 27, 2016 at 06:39:46AM -0700, Guenter Roeck wrote:
>> On 06/27/2016 05:13 AM, Heikki Krogerus wrote:
>>> Hi,
>>>
>>> On Mon, Jun 27, 2016 at 03:51:08PM +0530, Rajaram R wrote:
>>>> May be I am missing user or usage of the driver.. I see this driver is
>>>> providing limited information of the Type-C connectors or the port
>>>> partner
>>>
>>> Yes, this interface can't provide directly information received from
>>> PD commands like Discover Identity. We will have to present the
>>> partners even when USB PD is not supported and in a consistent
>>> fashion. Some details will be available in any case indirectly. Like
>>> if there are modes, there will be devices presenting them, and the
>>> product type in case of partners will be the partner type.
>>>
>>> But there are a couple of attributes I have been thinking about adding
>>> for the partners:
>>>
>>>           supported_data_roles
>>>           supports_usb_power_delivery
>>>
>>> The supported data roles would respond bits 30 and 31 of the ID Header
>>> VDO. But when the partner does not support USB PD, we will have to
>>> report "unknown" in it.
>>>
>>
>> Or make the attribute invisible in that case.
>
> Well, why not. I did not like the idea of hiding an attribute
> previously. I preferred to have an attribute always available, unless
> there was a single and clear way to determine the cases where any of
> the attributes for example with our partners would be visible or not..
> But who cares.
>

It would be visible if supports_usb_power_delivery is true. Doesn't that
match your requirements ?

>>> Oliver, Guenter! How do you guys feel about those? Is there any use
>>> for them?
>>>
>> Definitely good for debugging and informational. On the top of my head,
>> I don't immediately see what a user would do with it, though, but then
>> it would not hurt either to have the information.
>>
>> I keep wondering if it would make sense to directly expose the ID header
>> VDO, similar to the alternate mode VDOs, in the partner node.
>
> Yes, it makes sense. I'll add an attribute for that.
>
> But since you proposed hiding the attributes, I'll add an attribute
> "supports_usb_power_deliver" in any case, and make the vdo attribute
> visible only if it returs 1. I'll also make the "accessory" attribute
> visible only in case the partner type is accessory.
>
Ok with me.

Thanks,
Guenter