linux-kernel - RE: [RFC PATCH 0/4] Implement USB device/host switch for Vybrid

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Date:	Wed, 30 Mar 2016 08:07:13 +0000
From:	Peter Chen <peter.chen@....com>
To:	"maitysanchayan@...il.com" <maitysanchayan@...il.com>
CC:	Stefan Agner <stefan@...er.ch>, Peter Chen <hzpeterchen@...il.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ivan.ivanov@...aro.org" <ivan.ivanov@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"marcel@...wiler.com" <marcel@...wiler.com>
Subject: RE: [RFC PATCH 0/4] Implement USB device/host switch for Vybrid

 
> 
> On 16-03-29 00:24:46, Peter Chen wrote:
> >
> > >
> > > On 2016-03-25 00:40, Peter Chen wrote:
> > > > On Tue, Mar 15, 2016 at 02:08:26PM +0530, Sanchayan Maity wrote:
> > > >> Hello Peter,
> > > >>
> > > >> The existing usage of extcon in Chipidea driver relies on OTG
> > > >> registers. In case of SoC with dual role device but not a true
> > > >> OTG controller, this does not work. Such SoC's should specify the
> > > >> existing CI_HDRC_DUAL_ROLE_NOT_OTG flag and do the role switch
> > > >> without checking any of the OTG registers in my opinion.
> > > >> This is the case for Vybrid which uses a Chipidea IP but does not
> > > >> have a true 5 pin OTG implemented.
> > > >
> > > > Sorry to reply you late due to my new born baby.
> > > >
> > > > Are you sure Vybrid is NOT OTG core? Afaik, it is uses the same IP
> > > > base with other Freescale SoCs, just the IP core is 2.40a.
> > > > When working at device mode, can you read vbus status through OTGSC?
> > > > And if there is an ID pin (input pin) for Vybrid? I mean SoC, not
> > > > the board.
> > >
> > > I think the IP is actually OTG capable, the registers are there, but
> > > the signals seem not to be available on the SoC package. That is also what
> the RM says...
> > >
> > > Quotes from the RM:
> > >
> > > "OTG controller should be treated as Dual role controller that
> > > allows the controller to act as either a Host or a device with no
> > > support for HNP/SRP."
> > >
> > > And later, in Chapter 11.1:
> > >
> > > "The USB is not a true OTG. It can be configured by software to
> > > function either as peripheral or as host. The ID pin, which is
> > > unique for OTG operation, is not present in this implementation.
> > > There are no five pin interface. The user will get four pin host/ device
> interface."
> > >
> >
> > Get it, thanks. I am doing a patch for covering this case and vbus always-on
> case.
> 
> If I may ask at this point, how would your implementation be covering this case
> for Vybrid?
> 

Yes, if the vbus and id status are from the extcon, it will not read register OTGSC.

Peter