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

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Message-ID: <20160330063246.GA16028@Sanchayan-Arch.toradex.int>
Date:	Wed, 30 Mar 2016 12:02:46 +0530
From:	maitysanchayan@...il.com
To:	Peter Chen <peter.chen@....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

Hello Peter,

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?

- Sanchayan.