linux-kernel - Re: [PATCH v17 2/3] usb: USB Type-C connector class

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Date:   Thu, 2 Mar 2017 19:13:02 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Mats Karrman <mats.dev.list@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Oliver Neukum <oneukum@...e.com>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v17 2/3] usb: USB Type-C connector class

On 03/02/2017 07:22 AM, Mats Karrman wrote:
> Hi Heikki,
>
> Good to see things are happening with Type-C!
>
> On 2017-02-21 15:24, Heikki Krogerus wrote:
>
>> ...
>> +When connected, the partner will be presented also as its own device under
>> +/sys/class/typec/. The parent of the partner device will always be the port it
>> +is attached to. The partner attached to port "port0" will be named
>> +"port0-partner". Full path to the device would be
>> +/sys/class/typec/port0/port0-partner/.
>
> A "/port0" too much?
>
>> +
>> +The cable and the two plugs on it may also be optionally presented as their own
>> +devices under /sys/class/typec/. The cable attached to the port "port0" port
>> +will be named port0-cable and the plug on the SOP Prime end (see USB Power
>> +Delivery Specification ch. 2.4) will be named "port0-plug0" and on the SOP
>> +Double Prime end "port0-plug1". The parent of a cable will always be the port,
>> +and the parent of the cable plugs will always be the cable.
>> +
>> +If the port, partner or cable plug support Alternate Modes, every supported
>> +Alternate Mode SVID will have their own device describing them. The Alternate
>> +Modes will not be attached to the typec class. The parent of an alternate mode
>> +will be the device that supports it, so for example an alternate mode of
>> +port0-partner will bees presented under /sys/class/typec/port0-partner/. Every
>
> bees?
>
>> +mode that is supported will have its own group under the Alternate Mode device
>> +named "mode<index>", for example /sys/class/typec/port0/<alternate mode>/mode1/.
>> +The requests for entering/exiting a mode can be done with "active" attribute
>> +file in that group.
>> +
>> ...
>
> I'm hoping to find time to upgrade the kernel and try these patches in my system.
>
> Looking forward, one thing I have run into is how to connect the typec driver with a
> driver for an alternate mode. E.g. the DisplayPort Alternate Mode specification
> includes the HPD (hot plug) and HPD-INT (hot plug interrupt) signals as bits in the
> Attention message. These signals are needed by the DisplayPort driver to know when to
> start negotiation etc.
> Have you got any thoughts on how to standardize such interfaces?
>

That really depends on the lower level driver. For Chromebooks, where the Type-C
Protocol Manager runs on the EC, we have an extcon driver which reports the pin states
to the graphics drivers and connects to the Type-C class code using the Type-C class
API. I still need to update, re-test, and publish that code. The published code in
https://chromium.googlesource.com/chromiumos/third_party/kernel/, branch chromeos-4.4,
shows how it can be done, though that code currently still uses the Android Type-C
infrastructure.

Guenter