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SubjectRe: [PATCH] usb: host: Use helper function to get endpoint
On Wed, Aug 24, 2022 at 11:57:25PM +0600, Khalid Masum wrote:
> On Wed, Aug 24, 2022 at 8:40 PM Alan Stern <stern@rowland.harvard.edu> wrote:
> >
> >
> > Even this is awkward. It's silly to look up the endpoint in a table
> > when you already know that it is endpoint 0. Just do:
> >
> > ep = &udev->ep0;
> >
> > with no need to check for NULL.
>
> After further checking, I realized that usb_device udev is created by
> ehset_single_step_set_feature and depends on usb_hcd and port. So I do
> not get why the endpoint is at udev->ep0. Can you help me with this?

udev is not a usb_device structure; it is a _pointer_ to a usb_device
structure. The pointer is created when ehset_single_step_set_feature()
calls usb_hub_find_child(), but the structure itself gets created long
before that, when the USB device is first detected and initialized.

You can see this happening where hub_port_connect() calls
usb_alloc_dev(). The ep0 field is filled in by hub_port_init() and the
routines it calls.

Alan Stern

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