linux-kernel - Re: [RFC PATCH 2/3] usb: typec: Add product_type sysfs attribute file for partners and cables

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Message-ID: <20201119111136.GB3774817@kuha.fi.intel.com>
Date:   Thu, 19 Nov 2020 13:11:36 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Benson Leung <bleung@...gle.com>
Cc:     Prashant Malani <pmalani@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH 2/3] usb: typec: Add product_type sysfs attribute
 file for partners and cables

Hi Benson,

On Wed, Nov 18, 2020 at 09:48:21AM -0800, Benson Leung wrote:
> > +What:		/sys/class/typec/<port>-partner/product_type
> > +Date:		December 2020
> > +Contact:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > +Description:	USB Power Delivery Specification defines a set of product types
> > +		for the partner devices. This file will show the product type of
> > +		the partner if it is known. Dual-role capable partners will have
> > +		both UFP and DFP product types defined, but only one that
> > +		matches the current role will be active at the time. If the
> > +		product type of the partner is not visible to the device driver,
> > +		this file will not exist.
> > +
> > +		When the partner product type is detected, or changed with role
> > +		swap, uvevent is also raised that contains PRODUCT_TYPE=<product
> > +		type> (for example PRODUCT_TYPE=hub).
> > +
> > +		Valid values:
> > +
> > +		UFP / device role
> > +		========================  ==========================
> > +		undefined		  -
> > +		hub			  PDUSB Hub
> > +		peripheral		  PDUSB Peripheral
> > +		psd			  Power Bank
> > +		ama			  Alternate Mode Adapter
> > +		vpd			  VCONN Powered USB Device
> 
> I have it on good authority that "vpd" is incorrectly categorized here,
> and for future proofing, we'd better not introduce vpd as a product
> type for UFP...
> 
> A vpd is actually more closely related to a "cable" than it is a "UFP."
> A closer reading of the USB Type-C and USB PD specs will reveal that
> VPDs can only ever appear as SOP' and not as SOP, so having its type
> appear under UFP is a mistake.
> 
> In other words, the USB PD V3.0 R2.0 spec is wrong. A change has been
> working its way through the spec committee to fix this, but it is not yet
> published.
> 
> In order to reduce the amount of churn, I would recommend not
> including vpd as a possible type until a new version of the spec (or the ECN)
> is published.

Thanks for the heads-up. I'll leave the vpd out then.

cheers,

-- 
heikki