Re: [PATCH] USB Core hub.c

>From: Alan Stern [mailto:[email protected]]
>On Mon, 21 May 2007, David Brownell wrote:
>> On Monday 21 May 2007, Vikram Pandita wrote:
>> > ---
>> > diff -purN -X ./dontdiff a/drivers/usb/core/hub.c
>> > b/drivers/usb/core/hub.c
>> > --- a/drivers/usb/core/hub.c    2007-05-13 14:24:43.000000000 +0530
>> > +++ b/drivers/usb/core/hub.c    2007-05-21 13:19:07.000000000 +0530
>> > @@ -2571,7 +2571,7 @@ loop:
>> >                 ep0_reinit(udev);
>> >                 release_address(udev);
>> >                 usb_put_dev(udev);
>> > -               if (status == -ENOTCONN)
>> > +               if ((status == -ENOTCONN) || (status == -ENODEV))
>> >                         break;
>> >         }
>
>This is wrong.  -ENOTCONN means what it says, that nothing is connected
>to the port.  So when it occurs we really do want to break out of the
>loop.
>
>On the other hand, -ENODEV means that there is a device but it doesn't
>match our preconceptions (maybe its speed has somehow changed or some
>other aspect is different).  Since there still is a device connected to
>the port, we don't want to break out of the loop.
>
>Did you notice any particular example where the port was unconnected
>and the code still tried to enumerate three times?

Yes. This is to fix the OTG HNP case. 

In OTG enabled environment when the b-device attached is not supported
by host (is_targeted() returns Zero), the host suspends to give chance
to device to become b-host. If this fix is not in place, then the host
tries to enumerate the attached device SET_CONFIG_TRIES times which is
not required.

Following is the snippet of the code already in place that does the HNP
and returns the error code to stop re-enumerations and the proposed
patch checks for this error code:

        if (!is_targeted(udev)) {

                /* Maybe it can talk to us, though we can't talk to it.
                 * (Includes HNP test device.)
                 */
                if (udev->bus->b_hnp_enable || udev->bus->is_b_host) {
                        err = __usb_port_suspend(udev,
udev->bus->otg_port);
                        if (err < 0)
                                dev_dbg(&udev->dev, "HNP fail, %d\n",
err);
                }
                err = -ENODEV;
                goto fail;
        }
>
Vikram Pandita


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