linux-kernel - Re: [PATCH 2/3] usb: type-c: USB Type-C Connector System Software Interface

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Date:	Wed, 17 Feb 2016 12:29:55 +0200
From:	Felipe Balbi <balbif@...il.com>
To:	Oliver Neukum <oneukum@...e.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:	Felipe Balbi <balbi@...nel.org>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 2/3] usb: type-c: USB Type-C Connector System Software Interface


Hi,

Oliver Neukum <oneukum@...e.com> writes:
> On Wed, 2016-02-17 at 09:58 +0200, Heikki Krogerus wrote:
>> On Tue, Feb 16, 2016 at 02:39:47PM +0100, Oliver Neukum wrote:
>> > On Tue, 2016-02-16 at 11:22 +0200, Heikki Krogerus wrote:
>> > > > That question has not been answered. It would be awkward for the OS
>> > > > to find itself in the slave role, which it is ill equipped for. So
>> > > > the data role should be switched before the new device is announced
>> > > > to user space. How is that handled?
>> > > 
>> > > In the class driver, once we add support for preselecting the role,
>> > > when the connection happens we compare the initial role to the
>> > > preselected one and execute swap if it differs. Only after that we
>> > > notify userspace.
>> > 
>> > Yes, but we need an API. We can't keep adding to it. So if that
>> > is to be supported, it needs to be defined now.
>> 
>> When you say API, do you mean the API the class provides to the
>> drivers? Or did you mean ABI which would be the sysfs in this case?
>
> The API to user space. That is the point. We cannot break user space.
> Once this sysfs API is upstream we are stuck with it.

yeah, in fact I have been wondering if sysfs is the best interface to
userspace. I talked with Heikki a few days back about this; I was
wondering if something like what the NFC folks did with netlink would be
better here.

-- 
balbi

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