usb/hub: allow hubs up to 31 children

Current Wireless USB host hardware (Intel i1480 for example) allows up
to 22 devices to connect, thus bringing up the max number of children
in the WUSB Host Controller to 22 'fake' ports. Upcoming hardware
might raise that limit.

Makes almost no difference to go to 31, as the bit arrays are
byte-aligned (plus an extra bit in general), so 22 bits fit in 4 bytes
as 31 do.

As well, the only other array that depends on USB_MAXCHILDREN is
'struct usb_hub->indicator'. By declaring it 'u8' instead of 'enum
hub_led_mode', we reduce the size of each entry from 4 bytes (in i386)
to 1, which will add as we when are doubling USB_MAXCHILDREN
(with 16 the size of that array is 64 bytes, with 31 would be 128; by
using u8 that goes down to 31 bytes).

Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/usb.h b/include/linux/usb.h
index 5482bfb3303d..e5cb1690975a 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -313,8 +313,13 @@ struct usb_bus {
 /* This is arbitrary.
  * From USB 2.0 spec Table 11-13, offset 7, a hub can
  * have up to 255 ports. The most yet reported is 10.
+ *
+ * Current Wireless USB host hardware (Intel i1480 for example) allows
+ * up to 22 devices to connect. Upcoming hardware might raise that
+ * limit. Because the arrays need to add a bit for hub status data, we
+ * do 31, so plus one evens out to four bytes.
  */
-#define USB_MAXCHILDREN		(16)
+#define USB_MAXCHILDREN		(31)
 
 struct usb_tt;