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

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Message-ID: <20160217075841.GA24649@kuha.fi.intel.com>
Date:	Wed, 17 Feb 2016 09:58:41 +0200
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Oliver Neukum <oneukum@...e.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

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?

For the sysfs I would image we can manage with the current files,
current_data_role and current_power_role. If somebody writes to them
when we are disconnected, we still callback the dr_swap or pr_swap
hooks, and make a rule that when disconnected, it means we are
setting the "preferred" roles.

Would that be OK? Or did I still misunderstood your question?


Thanks,

-- 
heikki