linux-kernel - Re: [PATHCv10 1/2] usb: USB Type-C connector class

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Date:   Wed, 16 Nov 2016 10:39:27 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Badhri Jagan Sridharan <badhri@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Bin Gao <bin.gao@...ux.intel.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Guenter Roeck <linux@...ck-us.net>,
        LKML <linux-kernel@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>
Subject: Re: [PATHCv10 1/2] usb: USB Type-C connector class

On Wed, 2016-11-16 at 11:30 +0200, Heikki Krogerus wrote:
> On Tue, Nov 15, 2016 at 04:19:10PM -0800, Badhri Jagan Sridharan wrote:

> > Is that too costly to have ?
> 
> Greg, could you give your opinion. In this case we do have attribute
> files that the user space can poll. Data role is the USB data role, so
> host or device, and it can change for example if the partner executes
> a swap. The same can happen with the power role.

IMHO the uevent is cheaper. User space cannot just poll without further
infrastructure. A task needs to run to poll. A uevent can be handled
through established infrastructure.
Sure from a kernel level it is the heavier gun, but I think this is
the wrong angle of looking at this issue.

	Regards
		Oliver