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    SubjectRe: [PATCH v6 01/12] usb: hcd: Initialize hcd->flags to 0
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    On 19/04/16 04:56, Peter Chen wrote:
    > On Mon, Apr 18, 2016 at 10:11:29AM -0400, Alan Stern wrote:
    >> On Mon, 18 Apr 2016, Peter Chen wrote:
    >>
    >>> On Wed, Apr 06, 2016 at 09:32:22AM +0300, Roger Quadros wrote:
    >>>> On 06/04/16 09:09, Felipe Balbi wrote:
    >>>>>
    >>>>> Hi,
    >>>>>
    >>>>> Roger Quadros <rogerq@ti.com> writes:
    >>>>>> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
    >>>>>> index 2ca2cef..6b1930d 100644
    >>>>>> --- a/drivers/usb/core/hcd.c
    >>>>>> +++ b/drivers/usb/core/hcd.c
    >>>>>> @@ -2706,6 +2706,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
    >>>>>> int retval;
    >>>>>> struct usb_device *rhdev;
    >>>>>>
    >>>>>> + hcd->flags = 0;
    >>>>>
    >>>>> seems like this would make more sense in usb_del_hcd() instead.
    >>>>>
    >>>>
    >>>> OK, I'll move it there.
    >>>>
    >>>
    >>> It depends on Alan's comments, whether only usb_add_hcd/usb_del_hcd
    >>> pair can be called repeat. If Alan acks it, I have no idea for it.
    >>
    >> Most of the host controller drivers were not written with this in mind,
    >> but I think it would be a good thing to allow. It would speed up the
    >> host/device role switches.
    >>
    >> This might mean we need to fix up several drivers to make them work
    >> correctly in an OTG environment. It should be possible to do this. Is
    >> there any particular reason why it would be difficult for Chipidea?
    >>
    >
    > I just want to do clean remove at OTG environment, like rmmod, so I did
    > this when I worked on chipidea OTG design.
    > I am worried if there are some resources dedicated for host device, eg,
    > clocks, gpio. etc.
    >
    > If OTG framework can know well hcd's add and remove, it is ok for chipidea
    > just calling usb_add_hcd/usb_del_hcd currently, but I suggested roger
    > adding platform hcd_ops as optional parameter in case the platform
    > has special requirement for hcd_ops.
    >
    We have 2 users now, omap + dwc3 and sh + EHCI/OHCI and we didn't seem to
    observe any issues with the usb_add/del_hcd approach.

    Let's keep things minimal for now. In the future, if users need something more
    we can always extend the framework.

    cheers,
    -roger

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