xhci: Clear EHB bit only at end of interrupt handler

l1k · l1k · commit 08b168fe59d9 · 2023-08-12T16:50:14.000+02:00
The Event Handler Busy bit shall be cleared by software when the Event Ring is empty. The xHC is thereby informed that it may raise another interrupt once it has enqueued new events (sec 4.17.2). However since commit dc0ffbe ("usb: host: xhci: update event ring dequeue pointer on purpose"), the EHB bit is already cleared after half a segment has been processed. As a result, spurious interrupts may occur: - xhci_irq() processes half a segment, clears EHB, continues processing remaining events. - xHC enqueues new events. Because EHB has been cleared, xHC sets Interrupt Pending bit. Interrupt moderation countdown begins. - Meanwhile xhci_irq() continues processing events. Interrupt moderation countdown reaches zero, so an MSI interrupt is signaled. - xhci_irq() empties the Event Ring, clears EHB again and is done. - Because an MSI interrupt has been signaled, xhci_irq() is run again. It discovers there's nothing to do and returns IRQ_NONE. Avoid by clearing the EHB bit only at the end of xhci_irq(). Fixes: dc0ffbe ("usb: host: xhci: update event ring dequeue pointer on purpose") Signed-off-by: Lukas Wunner <lukas@wunner.de> Cc: stable@vger.kernel.org # v5.5+ Cc: Peter Chen <peter.chen@nxp.com>
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
@@ -3021,7 +3021,8 @@ static int xhci_handle_event(struct xhci_hcd *xhci)
  * - To avoid "Event Ring Full Error" condition
  */
 static void xhci_update_erst_dequeue(struct xhci_hcd *xhci,
-		union xhci_trb *event_ring_deq)
+				     union xhci_trb *event_ring_deq,
+				     bool clear_ehb)
 {
 	u64 temp_64;
 	dma_addr_t deq;
@@ -3047,7 +3048,8 @@ static void xhci_update_erst_dequeue(struct xhci_hcd *xhci,
 	}
 
 	/* Clear the event handler busy flag (RW1C) */
-	temp_64 |= ERST_EHB;
+	if (clear_ehb)
+		temp_64 |= ERST_EHB;
 	xhci_write_64(xhci, temp_64, &xhci->ir_set->erst_dequeue);
 }
 
@@ -3120,7 +3122,7 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd)
 	while (xhci_handle_event(xhci) > 0) {
 		if (event_loop++ < xhci->event_ring->trbs_per_seg / 2)
 			continue;
-		xhci_update_erst_dequeue(xhci, event_ring_deq);
+		xhci_update_erst_dequeue(xhci, event_ring_deq, false);
 		event_ring_deq = xhci->event_ring->dequeue;
 
 		/* ring is half-full, force isoc trbs to interrupt more often */
@@ -3130,7 +3132,7 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd)
 		event_loop = 0;
 	}
 
-	xhci_update_erst_dequeue(xhci, event_ring_deq);
+	xhci_update_erst_dequeue(xhci, event_ring_deq, true);
 	ret = IRQ_HANDLED;
 
 out:
