only ask for 128 bytes of the first descriptor.  if this isn't
the complete descriptor, keep asking for more in 128-byte
chunks until we hit 4k or have the whole thing.
also, don't set the leds on a mouse.  :-)

Reference: /n/atom/patch/applied/usbkbsmalldesc
Date: Tue Apr  1 04:22:30 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/usb/kb/kb.c	Tue Apr  1 04:21:40 2014
+++ /sys/src/cmd/usb/kb/kb.c	Tue Apr  1 04:21:41 2014
@@ -184,7 +184,7 @@
 static int ptrrepvals(KDev *kd, Chain *ch, int *px, int *py, int *pb);
 
 static int
-setbootproto(KDev* f, int eid, uchar *, int)
+setbootproto(KDev* f, int eid, uchar **)
 {
 	int nr, r, id;
 
@@ -213,18 +213,56 @@
 	return usbcmd(f->dev, r, Setreport, Reportout | Ledreport, id, led, 1);
 }
 
-static uchar ignoredesc[128];
+int
+fullreportdesc(uchar *p, int n)
+{
+	int i, dsize;
+
+	for(i = 0; i < n; i += dsize+1){
+		dsize = (1 << (p[i] & 3)) >> 1;
+		if(p[i] == HidEnd)
+			return 1;
+	}
+	return 0;
+}
 
 static int
-setfirstconfig(KDev* f, int eid, uchar *desc, int descsz)
+usbcmdcfg(Dev *d, int type, int req, int value, int index, uchar **data)
 {
+	uchar *p;
+	int a, n;
+
+	assert((type & Rd2h) == Rd2h);
+	*data = nil;
+	p = nil;
+
+	for(a = 128; a < 4096; a += 128){
+		p = realloc(p, a);
+		n = usbcmd(d,  type, req, value, index, p, a);
+		if(n <= 0){
+			free(p);
+			return -1;
+		}
+		if(fullreportdesc(p, n)){
+			*data = p;
+			return n;
+		}
+	}
+	free(p);
+	return 0;
+}
+
+static int
+setfirstconfig(KDev* f, int eid, uchar **desc)
+{
+	uchar *ignore, *p;
 	int nr, r, id, i;
 
 	dprint(2, "setting first config %d\n", eid);
-	if(desc == nil){
-		descsz = sizeof ignoredesc;
-		desc = ignoredesc;
-	}
+	if(desc == nil)
+		desc = &ignore;
+	*desc = nil;
+
 	id = f->dev->usb->ep[eid]->iface->id;
 	r = Rh2d | Rstd | Rdev;
 	nr = usbcmd(f->dev,  r, Rsetconf, 1, 0, nil, 0);
@@ -235,18 +273,21 @@
 	if(nr < 0)
 		return -1;
 	r = Rd2h | Rstd | Riface;
-	nr=usbcmd(f->dev,  r, Rgetdesc, Dreport<<8, id, desc, descsz);
+	nr = usbcmdcfg(f->dev,  r, Rgetdesc, Dreport<<8, id, desc);
 	if(nr <= 0)
 		return -1;
 	if(f->debug){
 		fprint(2, "report descriptor:");
+		p = *desc;
 		for(i = 0; i < nr; i++){
 			if(i%8 == 0)
 				fprint(2, "\n\t");
-			fprint(2, "%#2.2ux ", desc[i]);
+			fprint(2, "%.2ux ", p[i]);
 		}
 		fprint(2, "\n");
 	}
+	if(desc == &ignore)
+		free(*desc);
 	f->ptrvals = ptrrepvals;
 	return nr;
 }
@@ -269,9 +310,9 @@
 		if(opendevdata(f->dev, ORDWR) >= 0){
 			if(f->bootp)
 				/* TODO func pointer */
-				setbootproto(f, f->eid, nil, 0);
+				setbootproto(f, f->eid, nil);
 			else
-				setfirstconfig(f, f->eid, nil, 0);
+				setfirstconfig(f, f->eid, nil);
 			break;
 		}
 		/* else usbd still working... */
@@ -679,6 +720,9 @@
 	threadsetname("kbd %s", f->ep->dir);
 	kbdfd = f->ep->dfd;
 
+	f->led = Lnum;
+	setled(f, f->led);
+
 	if(f->ep->maxpkt < 3 || f->ep->maxpkt > sizeof buf)
 		kbfatal(f, "weird maxpkt");
 
@@ -745,7 +789,7 @@
 static void
 kbstart(Dev *d, Ep *ep, Kin *in, void (*f)(void*), KDev *kd)
 {
-	uchar desc[512];
+	uchar *desc, otghack[128];
 	int n, res;
 
 	qlock(&inlck);
@@ -774,23 +818,24 @@
 		 * Set nonzero idle time to return more frequent reports
 		 * of keyboard state, to avoid losing key up/down events.
 		 */
-		n = read(d->cfd, desc, sizeof desc - 1);
+		n = read(d->cfd, otghack, sizeof otghack - 1);
 		if(n > 0){
-			desc[n] = 0;
-			if(strstr((char*)desc, "dwcotg") != nil)
+			otghack[n] = 0;
+			if(strstr((char*)otghack, "dwcotg") != nil)
 				kd->idle = Dwcidle;
 		}
 	}
 	res = -1;
 	if(!kd->bootp){
-		n = setfirstconfig(kd, ep->id, desc, sizeof desc);
+		n = setfirstconfig(kd, ep->id, &desc);
 		if(n > 0)
 			res = parsereportdesc(&kd->templ, desc, n);
+		free(desc);
 	}
 	/* if we could not set the first config, we give up */
 	if(kd->bootp || res < 0){
 		kd->bootp = 1;
-		if(setbootproto(kd, ep->id, nil, 0) < 0){
+		if(setbootproto(kd, ep->id, nil) < 0){
 			fprint(2, "kb: %s: bootproto: %r\n", d->dir);
 			return;
 		}
@@ -802,9 +847,6 @@
 		kd->ep = nil;
 		return;
 	}
-
-	kd->led = Lnum;
-	setled(kd, kd->led);
 
 	incref(d);
 	proccreate(f, kd, Stack);