Commit 15f3ef07 authored by Lukas Wunner's avatar Lukas Wunner Committed by Greg Kroah-Hartman
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xhci: Clear EHB bit only at end of interrupt handler 



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 dc0ffbea ("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: dc0ffbea ("usb: host: xhci: update event ring dequeue pointer on purpose")
Signed-off-by: default avatarLukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org # v5.5+
Cc: Peter Chen <peter.chen@kernel.org>
Signed-off-by: default avatarMathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20230915143108.1532163-4-mathias.nyman@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d7cdfc31

drivers/usb/host/xhci-ring.c

+7 −5
Original line number Diff line number Diff line
@@ -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;
@@ -3017,11 +3018,12 @@ static void xhci_update_erst_dequeue(struct xhci_hcd *xhci, 
			return;



		/* Update HC event ring dequeue pointer */

		temp_64 &= ERST_PTR_MASK;

		temp_64 &= ERST_DESI_MASK;

		temp_64 |= ((u64) deq & (u64) ~ERST_PTR_MASK);

	}



	/* Clear the event handler busy flag (RW1C) */

	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: