linux-kernel - Re: [PATCH v10 2/7] usb: mux: add generic code for dual role port mux

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Date:	Tue, 7 Jun 2016 15:49:11 +0300
From:	Roger Quadros <rogerq@...com>
To:	Lu Baolu <baolu.lu@...ux.intel.com>, Jun Li <jun.li@....com>,
	Peter Chen <hzpeterchen@...il.com>
CC:	"felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lee Jones <lee.jones@...aro.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 2/7] usb: mux: add generic code for dual role port mux

On 07/06/16 12:27, Lu Baolu wrote:
> Hi,
> 
> On 06/07/2016 02:34 PM, Jun Li wrote:
>>>> On 06/07/2016 11:03 AM, Jun Li wrote:
>>>>>> Hi Roger
>>>>>>
>>>>>>>>
>>>>>>>> For Mux devices implementing dual-role, the mux device driver _must_
>>>>>>>> use OTG/dual-role core API so that a common ABI is presented to user
>>>>>>>> space for OTG/dual-role.
>>>>>> That's the only point we have concern, do dual role switch through
>>>>>> OTG/dual-role core, not do it by itself.
>>>>
>>>> That really depends on how do you define "dual role". Can you please
>>>> provide an unambiguous definition of "dual role" used in OTG/dual-role
>>>> framework?
>> Host and peripheral.
>>
> 
> This is definitely ambiguous.
> 
> By reading OTG/dual-role code, my understanding is that "dual-role" is a
> "reduced OTG" which is for DRD devices lacking of some OTG negotiation
> protocols.

DRD means dual role with zero OTG features, which is similar to just host and
peripheral mode.

> 
> We really can't say "it's the scope of OTG/dual-role" whenever it comes to
> "host and peripheral".

What other combination you foresee?

cheers,
-roger