FAILED: patch "[PATCH] xhci: Clear EHB bit only at end of interrupt handler" failed to apply to 4.14-stable tree

The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.14.y
git checkout FETCH_HEAD
git cherry-pick -x 15f3ef070933817fac2bcbdb9c85bff9e54e9f80
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023101549-kudos-jitters-a76f@gregkh' --subject-prefix 'PATCH 4.14.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 15f3ef070933817fac2bcbdb9c85bff9e54e9f80 Mon Sep 17 00:00:00 2001
From: Lukas Wunner <[email protected]>
Date: Fri, 15 Sep 2023 17:31:07 +0300
Subject: [PATCH] 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 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().

index 98389b568633..3e5dc0723a8f 100644
@@ -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;

@@ -3017,12 +3018,13 @@ 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) */
-	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: