diff mbox series

xhci: Clear EHB bit only at end of interrupt handler

Message ID 0e26fb1421216b198a89b9164ab6c4cd9e1e127a.1692049324.git.lukas@wunner.de
State Superseded
Headers show
Series xhci: Clear EHB bit only at end of interrupt handler | expand

Commit Message

Lukas Wunner Aug. 15, 2023, 7:20 a.m. UTC 
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 dc0ffbea5729 ("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: dc0ffbea5729 ("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>
---
 drivers/usb/host/xhci-ring.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 1dde53f..bc6280b 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2996,7 +2996,8 @@  static int xhci_handle_event(struct xhci_hcd *xhci, struct xhci_interrupter *ir)
  */
 static void xhci_update_erst_dequeue(struct xhci_hcd *xhci,
 				     struct xhci_interrupter *ir,
-				     union xhci_trb *event_ring_deq)
+				     union xhci_trb *event_ring_deq,
+				     bool clear_ehb)
 {
 	u64 temp_64;
 	dma_addr_t deq;
@@ -3022,7 +3023,8 @@  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, &ir->ir_set->erst_dequeue);
 }
 
@@ -3103,7 +3105,7 @@  irqreturn_t xhci_irq(struct usb_hcd *hcd)
 	while (xhci_handle_event(xhci, ir) > 0) {
 		if (event_loop++ < TRBS_PER_SEGMENT / 2)
 			continue;
-		xhci_update_erst_dequeue(xhci, ir, event_ring_deq);
+		xhci_update_erst_dequeue(xhci, ir, event_ring_deq, false);
 		event_ring_deq = ir->event_ring->dequeue;
 
 		/* ring is half-full, force isoc trbs to interrupt more often */
@@ -3113,7 +3115,7 @@  irqreturn_t xhci_irq(struct usb_hcd *hcd)
 		event_loop = 0;
 	}
 
-	xhci_update_erst_dequeue(xhci, ir, event_ring_deq);
+	xhci_update_erst_dequeue(xhci, ir, event_ring_deq, true);
 	ret = IRQ_HANDLED;
 
 out: