linux-kernel - RE: [PATCH v11 08/14] usb: otg: add OTG/dual-role core

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Date:	Thu, 23 Jun 2016 07:42:05 +0000
From:	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:	Roger Quadros <rogerq@...com>, Felipe Balbi <balbi@...nel.org>,
	Peter Chen <hzpeterchen@...il.com>
CC:	"peter.chen@...escale.com" <peter.chen@...escale.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
	"sergei.shtylyov@...entembedded.com" 
	<sergei.shtylyov@...entembedded.com>,
	"jun.li@...escale.com" <jun.li@...escale.com>,
	"grygorii.strashko@...com" <grygorii.strashko@...com>,
	"robh@...nel.org" <robh@...nel.org>,
	"nsekhar@...com" <nsekhar@...com>, "b-liu@...com" <b-liu@...com>,
	"joe@...ches.com" <joe@...ches.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH v11 08/14] usb: otg: add OTG/dual-role core

Hi Roger-san,

< snip >
> >>>> commit 11c011a5e777c83819078a18672543f04482b3ec
> >>>> Author: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> >>>> Date:   Thu May 19 11:12:56 2016 +0100
> >>>>
> >>>>     usb: echi-hcd: Add ehci_setup check before echi_shutdown
> >>>>
> >>>>
> >>>>
> >>>> In some cases, the USB code (gadget/hcd->start/stop) needs to be called
> >>>> during the role swap. For example, if you have mux driver, you may
> >>>> need to call usb_remove_hcd when ID from 0 to 1. Without Roger's framework,
> >>>> how can we do that?
> >>>
> >>> You don't really need to remove the gadget. Just mask its interrupts and
> >>> ignore any calls to any gadget_driver ops, right? Likewise for
> >>> XHCI. Just clear RUN/STOP and no events will ever reach XHCI. But, from
> >>> the point of view of dwc3, it's simpler to unregister the platform
> >>> device we create for xhci-plat.c. I need no changes in XHCI to do that
> >>> and driver model will make sure to call xhci-plat's ->remove() which
> >>> will handle everything for me correctly.
> >>>
> >>
> >> I admit it can do in a IP driver, eg both host and peripheral for the
> >> single IP, eg chipidea, dwc3, etc. But how can we clear RUN/STOP bit
> >> or what else for HCD at mux driver?
> >
> > dwc3's OTG block has control of that, however, what I'll do is
> > platform_device_del() xhci-plat's device. Not one line changes inside
> > XHCI.
> >
> 
> Let's talk about how non dwc3 based platforms can get it done.
> 
> Yoshihiro-san, could you please share your platform requirements from dual-role
> perspective?

My platform requirements about dual-role are:
- Initial settings of all host, gadget and OTG IP registers are needed before enters [AB]-device recognition procedure.
- In the recognition procedures, a software needs:
 - to check ID pin related register in OTG
 - to set OTG IP registers to change the role
  - and then host or gadget can start.
- In the disconnect detection procedures, a software needs similar checkings/settings with the recognition.

Best regards,
Yoshihiro Shimoda

> cheers,
> -roger