linux-kernel - Re: [RFC PATCHv2] usb: USB Type-C Connector Class

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Date:	Mon, 6 Jun 2016 16:28:08 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Oliver Neukum <oneukum@...e.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Rajaram R <rajaram.officemail@...il.com>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class

On Fri, Jun 03, 2016 at 11:39:27AM -0700, Guenter Roeck wrote:
> On Fri, Jun 03, 2016 at 06:17:46PM +0300, Heikki Krogerus wrote:
> [ ... ]
> > > > > 
> > > > > In my test case, this gives me
> > > > >      /sys/class/type-c/usbc0/
> > > > > 	usbc0.svid:18d1
> > > > > 	usbc0.svid:18d1/mode0
> > > > > 	usbc0.svid:18d1/mode0/vdo
> > > > > 	usbc0.svid:18d1/mode0/description
> > > > > 	usbc0.svid:18d1/mode0/active
> > > > > 	...
> > > > > 	usbc0.svid:ff01
> > > > > 	usbc0.svid:ff01/mode0/vdo
> > > > > 	usbc0.svid:ff01/mode0/description
> > > > > 	usbc0.svid:ff01/mode0/active
> > > 
> > > Side note: I didn't provide a description/name for the modes, because that
> > > would result in something like usbc0.DisplayPort/ instead of usbc0.svid:ff01/,
> > > and I prefer a consistent ABI. Since this _is_ part of the ABI, would it make
> > > sense to standardize on names for modes in sysfs ? For example, how should
> > > a "Display Port" mode directory be named ? It doesn't sound good if I
> > > use "usbc0.svid:ff01", someone else uses "usbc0.DisplayPort", and yet
> > > someone else uses "usbc0.displayport".
> > 
> > Yeah, let's make them standard.
> > 
> Any name preferences ?

I would prefer lower case letters. I don't know the SIDs there are at
them moment, other then Display Port. Do you know them?

I don't think we can ever guarantee that in every case we will be able
to provide a human readable name for the alternate modes if they are
vendor defined. We will then potentially still have the names in two
different forms: "usbc0.displayport" and "usbc0.svid:xxxx". Is that
something acceptable to everybody?

I guess if it's not, then to only way to go forward would be to always
just use the svid in the name.

> > > Also, do we at some point need to standardize the ABI for the standard
> > > alternate modes such as DisplayPort (if there are any - again I am not
> > > there yet) ?
> > 
> > I don't have an answer to that.
> > 
> Ok, I'll look into it as I proceed with my implementation.
> 
> > > 
> > > Sounds good to me. Many other subsystems do the same, ie create the subsystem
> > > device(s) during registration with the subsystem, so this is in line with other
> > > kernel code.
> > > 
> > > Should I send you a follow-up patch on top of yours ?
> > 
> > Sure. I'm a little bit stuck with an other tasks, so let's keep this
> > thing rolling.
> > 
> See below.

Thanks. I pushed it to my work branch for this class:

https://github.com/krohei/linux/commits/typec_class

There are still a few open questions, but I'm in any case going to
start polishing the driver. I think the other attributes are more or
less decided, excluding the alternate modes.


Cheers,

-- 
heikki