linux-kernel - Re: [PATCHv3 1/2] usb: USB Type-C connector class

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Message-ID: <20160629103034.GB6915@kuha.fi.intel.com>
Date:	Wed, 29 Jun 2016 13:30:34 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Rajaram R <rajaram.officemail@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Oliver Neukum <oneukum@...e.com>,
	Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCHv3 1/2] usb: USB Type-C connector class

On Wed, Jun 29, 2016 at 02:21:10PM +0530, Rajaram R wrote:
> On Mon, Jun 27, 2016 at 5:43 PM, Heikki Krogerus
> <heikki.krogerus@...ux.intel.com> wrote:
> > Hi,
> >
> > On Mon, Jun 27, 2016 at 03:51:08PM +0530, Rajaram R wrote:
> >> May be I am missing user or usage of the driver.. I see this driver is
> >> providing limited information of the Type-C connectors or the port
> >> partner
> >
> > Yes, this interface can't provide directly information received from
> > PD commands like Discover Identity. We will have to present the
> > partners even when USB PD is not supported and in a consistent
> > fashion. Some details will be available in any case indirectly. Like
> > if there are modes, there will be devices presenting them, and the
> > product type in case of partners will be the partner type.
> 
> Agree. What is the end use of this driver? IMO end use case will
> decide what attributes to be shared.  Since we are terming this as a
> universal representation for user space we may need to expose details
> such as Discovery details say Vendor ID, Product ID, Super Speed
> support etc which are not related to alt mode.  In the legacy drivers
> complete descriptors of the device is available for user space to
> build applications.

The details about the USB connection are out side the scope the this
class, and in most cases the port driver will not even have them at
their disposal. We can determine that the connector is in USB mode,
and that's about it.

But those details will in any case be exposed by the USB subsystem, so
why should we duplicate them? The user space has been so far relying
on getting the details from the normal interfaces the USB subsystem
provides and that should not change.


Thanks,

-- 
heikki