Fix an issue with 11g beacon frames which looks to be a limitation

on the largest multi-write size.

From the submitter:

==
I looked further into the magic 88-byte threshold after which the bug
occurs.  It turns out that figure included the 24-byte tx_desc, and up
to 64 bytes of beacon frame (header+data).

rum_write_multi doesn't seem happy with writing >64 bytes at a time to
the MAC register.  If I break it up into separate calls (e.g. bytes
0-63, then bytes 64-65, written at the appropriate offset) I see the
proper beacon frames being transmitted now.
==

Submitted by:	Steven Chamberlain <steven@pyro.eu.org>
MFC after:	3 days

1 files changed, 13 insertions, 8 deletions

diff --git a/sys/dev/usb/wlan/if_rum.c b/sys/dev/usb/wlan/if_rum.c
index 5a69792..87d92aa 100644
--- a/sys/dev/usb/wlan/if_rum.c
+++ b/sys/dev/usb/wlan/if_rum.c
@@ -1407,20 +1407,25 @@ rum_write_multi(struct rum_softc *sc, uint16_t reg, void *buf, size_t len)
 {
 	struct usb_device_request req;
 	usb_error_t error;
+	int offset;
 
 	req.bmRequestType = UT_WRITE_VENDOR_DEVICE;
 	req.bRequest = RT2573_WRITE_MULTI_MAC;
 	USETW(req.wValue, 0);
-	USETW(req.wIndex, reg);
-	USETW(req.wLength, len);
 
-	error = rum_do_request(sc, &req, buf);
-	if (error != 0) {
-		device_printf(sc->sc_dev,
-		    "could not multi write MAC register: %s\n",
-		    usbd_errstr(error));
+	/* write at most 64 bytes at a time */
+	for (offset = 0; offset < len; offset += 64) {
+		USETW(req.wIndex, reg + offset);
+		USETW(req.wLength, MIN(len - offset, 64));
+
+		error = rum_do_request(sc, &req, buf + offset);
+		if (error != 0) {
+			device_printf(sc->sc_dev,
+			    "could not multi write MAC register: %s\n",
+			    usbd_errstr(error));
+			return (error);
+		}
 	}
-	return (error);
 }
 
 static void