[PATCH] ohci-hcd, fix urb unlink races

This patch:

- Fixes a longstanding urb unlink race, by switching to a single queue
  for EDs being unlinked.  The previous two-queue scheme was sensitive to
  IRQ latencies:  one extra millisecond would make it use the wrong queue.
  This updated scheme should handle latencies of up to 32K microseconds
  (Cthulu forfend :) and slightly shrinks object code size.

- Related (mostly) cleanup.  Some functions and one ED field renamed, ED
  layout is a smidgeon more compact (even given more data), driver version
  string doesn't reflect CVS, debug message only comes out in verbose mode.

drivers/usb/host/ohci-hcd.c

@@ -12,6 +12,9 @@
  * 
  * History:
  * 
+ * 2002/06/01 remember frame when HC won't see EDs any more; use that info
+ *	to fix urb unlink races caused by interrupt latency assumptions;
+ *	minor ED field and function naming updates
  * 2002/01/18 package as a patch for 2.5.3; this should match the
  *	2.4.17 kernel modulo some bugs being fixed.
  *
@@ -106,7 +109,7 @@
  *	- lots more testing!!
  */
 
-#define DRIVER_VERSION "$Revision: 1.9 $"
+#define DRIVER_VERSION "2002-Jun-01"
 #define DRIVER_AUTHOR "Roman Weissgaerber <weissg@vienna.at>, David Brownell"
 #define DRIVER_DESC "USB 1.1 'Open' Host Controller (OHCI) Driver"
 
@@ -287,7 +290,7 @@ static int ohci_urb_dequeue (struct usb_hcd *hcd, struct urb *urb)
 		}
 			
 		urb_priv->state = URB_DEL; 
-		ed_unlink (urb->dev, urb_priv->ed);
+		start_urb_unlink (ohci, urb_priv->ed);
 		spin_unlock_irqrestore (&ohci->lock, flags);
 	} else {
 		/*
@@ -508,16 +511,15 @@ static void ohci_irq (struct usb_hcd *hcd)
   
 	/* could track INTR_SO to reduce available PCI/... bandwidth */
 
-	// FIXME:  this assumes SOF (1/ms) interrupts don't get lost...
-	if (ints & OHCI_INTR_SF) { 
-		unsigned int frame = le16_to_cpu (ohci->hcca->frame_no) & 1;
+	/* handle any pending URB/ED unlinks, leaving INTR_SF enabled
+	 * when there's still unlinking to be done (next frame).
+	 */
+	spin_lock (&ohci->lock);
+	if (ohci->ed_rm_list)
+		finish_unlinks (ohci, le16_to_cpu (ohci->hcca->frame_no));
+	if ((ints & OHCI_INTR_SF) != 0 && !ohci->ed_rm_list)
 		writel (OHCI_INTR_SF, &regs->intrdisable);	
-		if (ohci->ed_rm_list [!frame] != NULL) {
-			dl_del_list (ohci, !frame);
-		}
-		if (ohci->ed_rm_list [frame] != NULL)
-			writel (OHCI_INTR_SF, &regs->intrenable);	
-	}
+	spin_unlock (&ohci->lock);
 
 	writel (ints, &regs->intrstatus);
 	writel (OHCI_INTR_MIE, &regs->intrenable);	
@@ -719,8 +721,7 @@ static int hc_restart (struct ohci_hcd *ohci)
 	for (i = 0; i < NUM_INTS; i++) ohci->hcca->int_table [i] = 0;
 	
 	/* no EDs to remove */
-	ohci->ed_rm_list [0] = NULL;
-	ohci->ed_rm_list [1] = NULL;
+	ohci->ed_rm_list = NULL;
 
 	/* empty control and bulk lists */	 
 	ohci->ed_isotail     = NULL;
@@ -802,7 +803,7 @@ static int ohci_resume (struct usb_hcd *hcd)
 		ohci->disabled = 0;
 		ohci->sleeping = 0;
 		ohci->hc_control = OHCI_CONTROL_INIT | OHCI_USB_OPER;
-		if (!ohci->ed_rm_list [0] && !ohci->ed_rm_list [1]) {
+		if (!ohci->ed_rm_list) {
 			if (ohci->ed_controltail)
 				ohci->hc_control |= OHCI_CTRL_CLE;
 			if (ohci->ed_bulktail)

drivers/usb/host/ohci.h

@@ -27,22 +27,29 @@ struct ed {
 	__u32			hwNextED;	/* next ED in list */
 
 	/* rest are purely for the driver's use */
-	struct ed		*ed_prev;  
-	__u8			int_period;
-	__u8			int_branch;
-	__u8			int_load; 
-	__u8			int_interval;
-	__u8			state;			// ED_{NEW,UNLINK,OPER}
+	dma_addr_t		dma;		/* addr of ED */
+	struct ed		*ed_prev;	/* for non-interrupt EDs */
+
+	u8			type; 		/* PIPE_{BULK,...} */
+	u8			interval;	/* interrupt, isochronous */
+	union {
+		struct intr_info {		/* interrupt */
+			u8	int_period;
+			u8	int_branch;
+			u8	int_load; 
+		};
+		u16		last_iso;	/* isochronous */
+	};
+
+	u8			state;		/* ED_{NEW,UNLINK,OPER} */
 #define ED_NEW 		0x00		/* unused, no dummy td */
 #define ED_UNLINK 	0x01		/* dummy td, maybe linked to hc */
 #define ED_OPER		0x02		/* dummy td, _is_ linked to hc */
 #define ED_URB_DEL  	0x08		/* for unlinking; masked in */
 
-	__u8			type; 
-	__u16			last_iso;
+	/* HC may see EDs on rm_list until next frame (frame_no == tick) */
+	u16			tick;
 	struct ed		*ed_rm_list;
-
-	dma_addr_t		dma;			/* addr of ED */
 } __attribute__ ((aligned(16)));
 
 #define ED_MASK	((u32)~0x0f)		/* strip hw status in low addr bits */
@@ -335,7 +342,7 @@ struct ohci_hcd {
 	struct ohci_hcca	*hcca;
 	dma_addr_t		hcca_dma;
 
-	struct ed		*ed_rm_list [2];	/* to be removed */
+	struct ed		*ed_rm_list;		/* to be removed */
 
 	struct ed		*ed_bulktail;		/* last in bulk list */
 	struct ed		*ed_controltail;	/* last in ctrl list */