Re: [PATCHv6 1/3] usb: USB Type-C connector class

From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Vincent Palatin <vpalatin@chromium.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Oliver Neukum <oneukum@suse.com>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	Bin Gao <bin.gao@linux.intel.com>,
	linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [PATCHv6 1/3] usb: USB Type-C connector class
Date: Mon, 29 Aug 2016 16:43:03 +0300	[thread overview]
Message-ID: <20160829134303.GB16924@kuha.fi.intel.com> (raw)
In-Reply-To: <5f073751-a725-09a2-79be-49709bcd2cf9@roeck-us.net>

On Mon, Aug 29, 2016 at 06:04:52AM -0700, Guenter Roeck wrote:
> Heikki,
> 
> On 08/26/2016 07:07 AM, Heikki Krogerus wrote:
> > 
> > > > > > +What:          /sys/class/typec/<port>-partner/type
> > > > > > +Date:          June 2016
> > > > > > +Contact:       Heikki Krogerus <heikki.krogerus@linux.intel.com>
> > > > > > +Description:
> > > > > > +               Shows the type of the partner. Can be one of the following:
> > > > > > +               - USB - When the partner is normal USB host/peripheral.
> > > > > > +               - Charger - When the partner has been identified as dedicated
> > > > > > +                           charger.
> > > > > > +               - Alternate Mode - When the partner supports Alternate Modes.
> > > > > > +               - Accessory - When the partner is one of the accessories with
> > > > > > +                             specific Accessory Mode defined in USB Type-C
> > > > > > +                             specification.
> > > > > 
> > > > > 
> > > > > where a dock would be classified ?
> > > > 
> > > > A dock is just USB PD capable device with a bunch of alternate modes
> > > > that is attached to the port. There is no specific identifier for a
> > > > "dock".
> > > 
> > > My remark was a bit too stern,
> > > I meant a dock might be 'USB' 'Charger' 'Alternate Mode' , all at the
> > > same time or alternately depending what you plug in.
> > > I don't really see those types as mutually exclusive.
> > 
> > So USB type means the partner does not have alternate modes (I'll
> > clear that in the documentation), Charger is a dedicated charger and
> > therefore can not be anything else (no USB, no alternate modes).
> > 
> 
> This is probably the most difficult attribute to support.
> 
> Many PD capable chargers support alternate modes (for firmware upgrades).
> As I mentioned earlier, it is difficult to match reported Type-C partner
> types (or really anything reported in the SVDM Identity command)
> to the above types.
> 
> Does it really make sense to deviate that much from the Type-C specification ?
> I can understand why you hesitate to use DFP / UFP, as those terms are
> really hard to understand for the non-initiated. However, here it is really
> difficult to even determine which value to set. The best I can come up with is
> 
> - Not PD capable. Report USB (obviously includes non-PD capable chargers)
> - PD capable, supports alternate modes. Report as Alternate Mode (including
>   PD chargers supporting alternate modes)
> - PD capable, does not support alternate modes. Report as Accessory if
>   connected as accessory, as charger if we the port is connected as sink,
>   USB otherwise
> 
> Overall this is quite vague and, especially for chargers, most of the time
> misses the point.
> 
> I would really prefer if we could stay closer to the specification in this
> case, and not try to merge multiple orthogonal attributes into one.

OK. So what would you propose?

Thanks,

-- 
heikki