Re: [patch 1/7] wusb: teach choose_address() about wireless devices

On Monday 06 August 2007, Alan Stern wrote:
> On Fri, 3 Aug 2007, Inaky Perez-Gonzalez wrote:
> 

> > + *
> > + * We add 2 as an offset for two reasons: (1) dev addr 0 is reserved
> > + * by USB for default address; (2) Linux's USB stack uses always #1 for
> > + * the root hub of the controller. So port 0 has address #2.
> 
> This comment is a little confusing since the code really adds 1, not 2:

> > +	if (udev->wusb) {
> > +		devnum = udev->portnum + 1;
> 
> See?  Besides, the USB specs I've run across define port numbers
> starting at 1, not 0.  Maybe the WUSB spec is different.

/me checks the patch (again) -- my bad in the comment. udev->portnum 
is 1 based (as USB says). ergo for +1 will make the device address be 
2 based. So default address is #0 (choose_address() won't use), root
hub is "port #0", device address #1, any other device is #2 or higher.

device_address - 2 yields the port index (0 based) for the WUSB code.

Fixed patch inlined

wusb: teach choose_address() about wireless devices

Modify choose_address() so it knows about our special scheme of
addressing WUSB devices (1:1 w/ port number).

Signed-off-by: Inaky Perez-Gonzalez <[email protected]>

---
 drivers/usb/core/hub.c |   34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

Index: linux.hg/drivers/usb/core/hub.c
===================================================================
--- linux.hg.orig/drivers/usb/core/hub.c	2007-07-31 12:18:53.000000000 -0700
+++ linux.hg/drivers/usb/core/hub.c	2007-07-31 12:18:58.000000000 -0700
@@ -1077,21 +1077,42 @@
 	spin_unlock_irqrestore(&device_state_lock, flags);
 }
 
+/*
+ * WUSB devices are simple: they have no hubs behind, so the mapping
+ * device <-> virtual port number becomes 1:1. Why? to simplify the
+ * life of the device connection logic in
+ * drivers/usb/wusbcore/devconnect.c. When we do the initial secret
+ * handshake we need to assign a temporary address in the unauthorized
+ * space. For simplicity we use the first virtual port number found to
+ * be free [drivers/usb/wusbcore/devconnect.c:wusbhc_devconnect_ack()]
+ * and that becomes it's address [X < 128] or its unauthorized address
+ * [X | 0x80].
+ *
+ * We add 1 as an offset to the one-based USB-stack port number
+ * (zero-based wusb virtual port index) for two reasons: (a) dev addr
+ * 0 is reserved by USB for default address; (b) Linux's USB stack
+ * uses always #1 for the root hub of the controller. So USB stack's
+ * port #1, which is wusb virtual-port #0 has address #2.
+ */
 static void choose_address(struct usb_device *udev)
 {
 	int		devnum;
 	struct usb_bus	*bus = udev->bus;
 
 	/* If khubd ever becomes multithreaded, this will need a lock */
-
-	/* Try to allocate the next devnum beginning at bus->devnum_next. */
-	devnum = find_next_zero_bit(bus->devmap.devicemap, 128,
-			bus->devnum_next);
-	if (devnum >= 128)
-		devnum = find_next_zero_bit(bus->devmap.devicemap, 128, 1);
-
-	bus->devnum_next = ( devnum >= 127 ? 1 : devnum + 1);
-
+	if (udev->wusb) {
+		devnum = udev->portnum + 1;
+		BUG_ON(test_bit(devnum, bus->devmap.devicemap));
+	} else {
+		/* Try to allocate the next devnum beginning at
+		 * bus->devnum_next. */
+		devnum = find_next_zero_bit(bus->devmap.devicemap, 128,
+					    bus->devnum_next);
+		if (devnum >= 128)
+			devnum = find_next_zero_bit(bus->devmap.devicemap,
+						    128, 1);
+		bus->devnum_next = ( devnum >= 127 ? 1 : devnum + 1);
+	}
 	if (devnum < 128) {
 		set_bit(devnum, bus->devmap.devicemap);
 		udev->devnum = devnum;
@@ -2522,6 +2541,7 @@
 		udev->speed = USB_SPEED_UNKNOWN;
  		udev->bus_mA = hub->mA_per_port;
 		udev->level = hdev->level + 1;
+		udev->wusb = hub_is_wusb(hub);
 
 		/* set the address */
 		choose_address(udev);


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