[PATCH] Re: bug in handling of highspeed usb HID devices

[Christian Krause]

Hi Greg,

On Thu, 13 Oct 2005 15:48:39 -0700, Greg KH wrote:
> On Wed, Oct 12, 2005 at 09:55:32PM +0200, Christian Krause wrote:
>> Here is a small patch which solves the whole problem:

> The patch is at the wrong level, and has spaces instead of tabs.
> And no "signed-off-by" line :(
> Take a look at Documentation/SubmittingPatches for how to create a patch
> that I can apply and forward on.

Please apologize the wrong format of the patch, here is the next
try. I also include the description why the change is necessary again:

During the development of an USB device I found a bug in the handling of
Highspeed HID devices in the kernel.

What happened?

Highspeed HID devices are correctly recognized and enumerated by the
kernel. But even if usbhid kernel module is loaded, no HID reports are
received by the kernel.

The output of the hardware USB analyzer told me that the host doesn't
even poll for interrupt IN transfers (even the "interrupt in" USB
transfer are polled by the host).

After some debugging in hid-core.c I've found the reason.

In case of a highspeed device, the endpoint interval is re-calculated in
driver/usb/input/hid-core.c:

line 1669:
             /* handle potential highspeed HID correctly */
             interval = endpoint->bInterval;
             if (dev->speed == USB_SPEED_HIGH)
                   interval = 1 << (interval - 1);

Basically this calculation is correct (refer to USB 2.0 spec, 9.6.6).
This new calculated value of "interval" is used as input for
usb_fill_int_urb:

line 1685:

            usb_fill_int_urb(hid->urbin, dev, pipe, hid->inbuf, 0,
                   hid_irq_in, hid, interval);

Unfortunately the same calculation as above is done a second time in 
usb_fill_int_urb in the file include/linux/usb.h:

line 933:
        if (dev->speed == USB_SPEED_HIGH)
                urb->interval = 1 << (interval - 1);
        else
                urb->interval = interval;

This means, that if the endpoint descriptor (of a high speed device)
specifies e.g. bInterval = 7, the urb->interval gets the value:

hid-core.c: interval = 1 << (7-1) = 0x40 = 64
urb->interval = 1 << (interval -1) = 1 << (63) = integer overflow

Because of this the value of urb->interval is sometimes negative and is
rejected in core/urb.c:
line 353:
                /* too small? */
                if (urb->interval <= 0)
                        return -EINVAL;

The conclusion is, that the recalculaton of the interval (which is
necessary for highspeed) should not be made twice, because this is
simply wrong. ;-)

Re-calculation in usb_fill_int_urb makes more sense, because it is the
most general approach. So it would make sense to remove it from
hid-core.c.

Because in hid-core.c the interval variable is only used for calling
usb_fill_int_urb, it is no problem to remove the highspeed
re-calculation in this file.

--------------------------------snip------------------------
--- linux-2.6.13.4/drivers/usb/input/hid-core.c.old	2005-10-12 21:29:29.000000000 +0200
+++ linux-2.6.13.4/drivers/usb/input/hid-core.c	2005-10-12 21:31:02.000000000 +0200
@@ -1667,11 +1667,6 @@ static struct hid_device *usb_hid_config
 		if ((endpoint->bmAttributes & 3) != 3)		/* Not an interrupt endpoint */
 			continue;
 
-		/* handle potential highspeed HID correctly */
-		interval = endpoint->bInterval;
-		if (dev->speed == USB_SPEED_HIGH)
-			interval = 1 << (interval - 1);
-
 		/* Change the polling interval of mice. */
 		if (hid->collection->usage == HID_GD_MOUSE && hid_mousepoll_interval > 0)
 			interval = hid_mousepoll_interval;

--------------------------------snip------------------------
Signed-off-by: Christian Krause <chkr@xxxxxxxxxxx>


I hope all things are ok now and I ask kindly for applying. 

> Also, what device needs this patch?  Is it a device that I can buy
> today?

Yes, just buy Avocent's DSR2030. It enumerates as a highspeed HID device.


Best regards,
Christian
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