must allocate from lo memory, and allocb doesn't guarentee this.

Reference: /n/atom/patch/applied/loallocb
Date: Wed Feb 26 02:22:24 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/usbohci.c	Wed Feb 26 02:22:15 2014
+++ /sys/src/nix/k10/usbohci.c	Wed Feb 26 02:22:18 2014
@@ -409,10 +409,66 @@
 		return 0;
 	pa = PADDR(p);
 	if(sizeof(pa) > 4 && pa > 0xffffffff)
-		panic("usb: ohci: highmemptr %#p", p);
+		panic("usb: ohci: highmemptr %#P", pa);
 	return pa;
 }
 
+enum {
+	Hdrspc		= 64,		/* leave room for high-level headers */
+	Bdead		= 0x51494F42,	/* "QIOB" */
+//	Align		= BLOCKALIGN,
+};
+
+/* this is the guts of ../port/qallocb.c */
+static Block*
+binit(uchar *p, int size, uchar** next)
+{
+	int n;
+	Block *b;
+
+	n = Align + ROUNDUP(size+Hdrspc, Align) + sizeof(Block);
+	b = (Block*)(p + n - sizeof(Block));	/* block at end of allocated space */
+	b->base = p;
+	b->next = nil;
+	b->list = nil;
+	b->free = nil;
+	b->flag = 0;
+
+	/* align base and bounds of data */
+	b->lim = (uchar*)(PTR2UINT(b) & ~(Align-1));
+
+	/* align start of writable data, leaving space below for added headers */
+	b->rp = b->lim - ROUNDUP(size, Align);
+	b->wp = b->rp;
+
+	if(b->rp < b->base || b->lim - b->rp < size)
+		panic("binit");
+	if(next != nil)
+		*next = p + n;
+	return b;
+}
+
+/*
+ * allocb may use memory outside the normal malloc arena
+ * this is so gross.
+ */
+static Block*
+loallocb(int size)
+{
+	uchar *p;
+
+	p = malloc(Align + ROUNDUP(size+Hdrspc, Align) + sizeof(Block));
+	assert(PADDR(p) <= 0xffffffff);
+	return binit(p, size, nil);
+}
+
+static void
+lofreeb(Block *b)
+{
+	if(b != nil)
+		free(b->base);
+}
+
 static void
 waitSOF(Ctlr *ub)
 {
@@ -630,7 +686,7 @@
 {
 	if(td == nil)
 		return;
-	freeb(td->bp);
+	lofreeb(td->bp);
 	td->bp = nil;
 	lock(&tdpool);
 	if(td->nexttd == 0x77777777)
@@ -1350,12 +1406,12 @@
 	Block *bp;
 
 	if(count <= PGSZ)
-		bp = allocb(count);
+		bp = loallocb(count);
 	else{
 		if(count > 2*PGSZ)
 			panic("ohci: transfer > two pages");
 		/* maximum of one physical page crossing allowed */
-		bp = allocb(count+PGSZ);
+		bp = loallocb(count+PGSZ);
 		bp->rp = (uchar*)ROUNDUP((uintptr)bp->rp, PGSZ);
 		bp->wp = bp->rp;
 	}
@@ -2002,14 +2058,14 @@
 		td = tdalloc();
 		td->ep = ep;
 		td->io = iso;
-		td->bp = allocb(ep->maxpkt);
+		td->bp = loallocb(ep->maxpkt);
 		td->anext = iso->atds;		/* link as avail */
 		iso->atds = td;
 		td->next = edtds;
 		edtds = td;
 	}
 	newed(ctlr, ep, iso, "iso");		/* allocates a dummy td */
-	iso->ed->tds->bp = allocb(ep->maxpkt);	/* but not its block */
+	iso->ed->tds->bp = loallocb(ep->maxpkt);	/* but not its block */
 	iso->ed->tds->next = edtds;
 	isodtdinit(ep, iso, iso->ed->tds);
 }