On Mon, 28 Oct 2013, Prasad Koya wrote:
> Hi
>
> I tried resetting usb device when it gets ETIMEDOUT during get
> descriptor. On second retry, I don't see timeout. Please see this
> patch:
>
> Index: linux-3.4/drivers/usb/core/hub.c
> ===================================================================
> --- linux-3.4.orig/drivers/usb/core/hub.c
> +++ linux-3.4/drivers/usb/core/hub.c
> @@ -3213,6 +3213,14 @@ hub_port_init (struct usb_hub *hub, stru
> r = -EPROTO;
> break;
> }
> +
> + if (r == -ETIMEDOUT) {
> + r = usb_reset_device(hdev);
> + if (r) {
> + dev_dbg(&udev->dev, "failed to reset usb %d\n", r);
> + }
> + }
> +
> if (r == 0)
> break;
> }
The patch has been whitespace-damaged. Besides, what is the point of
calling usb_reset_device()? You might as well just break out of the
loop, because just after the end of the loop there is a call to
hub_port_reset().
In addition, you run the risk of infinite recursion since
usb_reset_device() calls usb_reset_and_verify_device(), which calls
hub_port_init().
Finally, the patch is wrong because it never does carry out the
Get-Device-Descriptor(64) request. That means it won't work with a
full-speed device if the ep0 maxpacket size is smaller than 64.
What you could do instead is this:
Index: usb-3.12/drivers/usb/core/hub.c
===================================================================
--- usb-3.12.orig/drivers/usb/core/hub.c
+++ usb-3.12/drivers/usb/core/hub.c
@@ -4106,11 +4106,12 @@ hub_port_init (struct usb_hub *hub, stru
r = -EPROTO;
break;
}
- if (r == 0)
+ if (r == 0) {
+ udev->descriptor.bMaxPacketSize0 =
+ buf->bMaxPacketSize0;
break;
+ }
}
- udev->descriptor.bMaxPacketSize0 =
- buf->bMaxPacketSize0;
kfree(buf);
retval = hub_port_reset(hub, port1, udev, delay, false);
@@ -4126,8 +4127,15 @@ hub_port_init (struct usb_hub *hub, stru
if (r != -ENODEV)
dev_err(&udev->dev, "device descriptor
read/64, error %d\n",
r);
- retval = -EMSGSIZE;
- continue;
+
+ /*
+ * For every speed except full speed, the
+ * ep0 maxpacket size is already known.
+ */
+ if (udev->speed == USB_SPEED_FULL) {
+ retval = -EMSGSIZE;
+ continue;
+ }
}
#undef GET_DESCRIPTOR_BUFSIZE
}
Alan Stern
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