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 17:27:42 +0800
From:	Lu Baolu <baolu.lu@...ux.intel.com>
To:	Jun Li <jun.li@....com>, Roger Quadros <rogerq@...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

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.

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

Best regards,
Lu Baolu