From 15f3ef070933817fac2bcbdb9c85bff9e54e9f80 Mon Sep 17 00:00:00 2001
From: Lukas Wunner <lukas@wunner.de>
Date: Fri, 15 Sep 2023 17:31:07 +0300
Subject: [PATCH] xhci: Clear EHB bit only at end of interrupt handler
Git-commit: 15f3ef070933817fac2bcbdb9c85bff9e54e9f80
References: git-fixes
Patch-mainline: v6.6-rc6

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@kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20230915143108.1532163-4-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>

---
 drivers/usb/host/xhci-ring.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2772,7 +2772,8 @@ static int xhci_handle_event(struct 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;
@@ -2793,12 +2794,13 @@ static void xhci_update_erst_dequeue(str
 			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) */
-	temp_64 |= ERST_EHB;
+	if (clear_ehb)
+		temp_64 |= ERST_EHB;
 	xhci_write_64(xhci, temp_64, &xhci->ir_set->erst_dequeue);
 }
 
@@ -2872,11 +2874,11 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd
 	while (xhci_handle_event(xhci) > 0) {
 		if (event_loop++ < TRBS_PER_SEGMENT / 2)
 			continue;
-		xhci_update_erst_dequeue(xhci, event_ring_deq);
+		xhci_update_erst_dequeue(xhci, event_ring_deq, false);
 		event_loop = 0;
 	}
 
-	xhci_update_erst_dequeue(xhci, event_ring_deq);
+	xhci_update_erst_dequeue(xhci, event_ring_deq, true);
 	event_ring_deq = xhci->event_ring->dequeue;
 	ret = IRQ_HANDLED;