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    SubjectRE: [PATCH v7 10/14] usb: otg: add hcd companion support
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    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.
    Or, does this topic assume an otg controller handles 2 EHCI controllers?
    I'm not sure such environment actually exists.

    > > 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.
    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.

    Best regards,
    Yoshihiro Shimoda

    > Alan Stern

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