Re: [PATCH] USB Core hub.c: prevent re-enumeration on HNP

>-----Original Message-----
>From: Alan Stern [mailto:[email protected]]
>Sent: Tuesday, May 22, 2007 7:45 PM
>To: Pandita, Vikram
>Cc: David Brownell; USB development list
>Subject: RE: [linux-usb-devel] [PATCH] USB Core hub.c
>
>On Tue, 22 May 2007, Pandita, Vikram wrote:
>
>> >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;
>>         }
>
>I understand.
>
>The problem is that hub_port_init() also returns -ENODEV under some
>circumstances where we don't want to break out of the loop.  So either
>you should change the code shown above to return something else (for
>example -EBADE) or else you should change hub_port_init().

New proposed patch based on your inputs:

Patch is to prevent the OTG host of doing 3 times enumeration of device when the Host suspends for HNP. The error code used in this case is ENOTSUPP.

Signed-off-by: Vikram Pandita <[email protected]>
---
diff -purN -X ./dontdiff a/drivers/usb/core/hub.c c/drivers/usb/core/hub.c
--- a/drivers/usb/core/hub.c    2007-05-13 14:24:43.000000000 +0530
+++ c/drivers/usb/core/hub.c    2007-05-23 11:58:40.000000000 +0530
@@ -1361,7 +1361,7 @@ int usb_new_device(struct usb_device *ud
                        if (err < 0)
                                dev_dbg(&udev->dev, "HNP fail, %d\n", err);
                }
-               err = -ENODEV;
+               err = -ENOTSUPP;
                goto fail;
        }
 #endif
@@ -2571,7 +2571,7 @@ loop:
                ep0_reinit(udev);
                release_address(udev);
                usb_put_dev(udev);
-               if (status == -ENOTCONN)
+               if ((status == -ENOTCONN) || (status == -ENOTSUPP))
                        break;
        }
---

>
>Alan Stern



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