Re: [PATCH v7 10/14] usb: otg: add hcd companion support

[Peter Chen]

On Thu, May 12, 2016 at 03:13:48PM +0300, Roger Quadros wrote:
> Hi,
> 
> On 12/05/16 13:31, Yoshihiro Shimoda wrote:
> > Hi,
> > 
> >> From: Roger Quadros
> >> Sent: Thursday, May 12, 2016 6:32 PM
> >>
> >> Hi,
> >>
> >> On 12/05/16 11:34, Roger Quadros wrote:
> >>> On 12/05/16 07:00, Yoshihiro Shimoda wrote:
> >>>> Hi,
> >>>>
> >>>>> From: Alan Stern
> >>>>> Sent: Wednesday, May 11, 2016 11:47 PM
> >>>>>
> >>>>> On Wed, 11 May 2016, Roger Quadros wrote:
> >>>>>
> >>>>>>> What I mean is if you have 2 EHCI controllers with 2 companion
> >>>>>>> controllers, don't you need to know which companion goes with which EHCI
> >>>>>>> controller? Just like you do for the otg-controller property.
> >>>>>>>
> >>>>>>
> >>>>>> That is a very good point. I'm not very sure and it seems that current code won't work
> >>>>>> with multiple EHCI + companion instances.
> >>>>
> >>>> I may misunderstand this topic, but if I use the following environment, it works correctly.
> >>>>
> >>>> < My environment >
> >>>> - an otg controller: Sets hcd-needs-companion.
> >>>> - ehci0 and ohci0 and a function: They connect to the otg controller using "otg-controller" property.
> >>>> - ehci1 and ohci1: No "otg-controller" property.
> >>>> - ehci2 and ohci2: No "otg-controller" property.
> >>>>
> >>>> In this environment, all hosts works correctly.
> >>>> Also I think if we have 2 otg controlelrs, it should be work because otg_dev instance differs.
> >>>
> >>> The topic is about more than one otg controllers and how to tie the right ehci and ohci
> >>> to the correct otg_dev instance especially in cases where we can't depend on probe order.
> >>>
> >>>> Or, does this topic assume an otg controller handles 2 EHCI controllers?
> >>>> I'm not sure such environment actually exists.
> >>>
> >>> No it is not about that.
> > 
> > Thank you for the reply. I understood it.
> > 
> >>>>>> Alan, does USB core even know which EHCI and OHCI are linked to the same port
> >>>>>> or the handoff is software transparent?
> >>>>>
> >>>>> The core knows.  It doesn't use the information for a whole lot of
> >>>>> things, but it does use it in a couple of places.  Search for
> >>>>> "companion" in core/hcd-pci.c and you'll see.
> >>>>
> >>>> Thank you for the information. I didn't know this code.
> >>>> If my understanding is correct, the core/hcd-pci.c code will not be used by non-PCI devices.
> >>>
> >>> That is correct.
> >>>
> >>>> In other words, nobody sets "hcd->self.hs_companion" if we use such a device.
> >>>> So, I will try to add such a code if needed.
> >>>
> >>> I think OTG core would have to rely on USB core in providing the right companion device,
> >>> just like we rely on it for the primary vs shared HCD case.
> >>>
> >>
> >> OK, it is not so simple.
> >>
> >> EHCI and companion port handoff is really meant to be software transparent.
> >>
> >> non-PCI devices really don't have knowledge of which OHCI instance is companion to the EHCI.
> >> With device tree we could provide this mapping but for non-device tree case we can't do
> >> anything.
> >>
> >> So my suggestion would be to keep dual role implementation limited to one instance for
> >> EHCI + companion case for non-DT.
> >> For PCI case I don't see how dual role can be implemented. I don't think we have any
> >> dual-role PCI cards.
> > 
> > R-Car Gen2 SoCs (r8a779[0134] / arm32) has USB 2.0 host controllers via PCI bus and
> > one high speed function controller via AXI bus.
> > One of channel can be used as host or function.
> > 
> >> For DT case we could have a DT binding to tie the EHCI and companion and use that
> >> in the OTG framework.
> 
> After looking at the code it seems we don't need this special binding as we are already
> linking the EHCI controller and companion controller to the single otg controller instance
> using the otg-controller property.
> 

Then, how you know this EHCI + companion controller special case during otg adds
hcd, it needs special handling, right?

Peter

> So all is good as of now.
> 
> For non DT case, it is the responsibility of platform support code to ensure that
> it calls usb_otg_add_hcd() with the correct otg controller instance for both EHCI and
> companion controller and things should work fine there as well.
> 
> --
> cheers,
> -roger
> 
> > 
> > R-Car Gen3 SoC (r8a7795 / arm64) will be this type.
> > (Both USB 2.0 host/function controllers connect to AXI bus.)
> > 
> >> Any objections?
> > 
> > I don't have any objections because I'm just focus on R-Car Gen3 SoC for now.
> > If someone needs for PCI case, I think it is possible to add such a code somehow later.
> > 
> > Best regards,
> > Yoshihiro Shimoda
> > 
> >> cheers,
> >> -roger
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-- 

Best Regards,
Peter Chen