usb: xhci: rework Event Ring Segment Table Size mask

JIRA: https://issues.redhat.com/browse/RHEL-116016

commit 7c6df26
Author: Niklas Neronin <niklas.neronin@linux.intel.com>
Date: Thu, 15 May 2025 16:56:15 +0300

  Event Ring Segment Table Size Register contain two fields:
   - Bits 15:0:	Event Ring Segment Table Size
   - Bits 31:16:	RsvdZ (Reserved and Zero)

  The current mask 'ERST_SIZE_MASK' refers to the RsvdZ bits (31:16).
  Change the mask to refer to bits 15:0, which are the Event Ring Segment
  Table Size bits.

  Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
  Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
  Link: https://lore.kernel.org/r/20250515135621.335595-19-mathias.nyman@linux.intel.com
  Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Desnes Nunes <desnesn@redhat.com>

Author: Desnes Nunes

drivers/usb/host/xhci-mem.c

@@ -1831,7 +1831,7 @@ xhci_remove_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir)
 	 */
 	if (ir->ir_set) {
 		tmp = readl(&ir->ir_set->erst_size);
-		tmp &= ERST_SIZE_MASK;
+		tmp &= ~ERST_SIZE_MASK;
 		writel(tmp, &ir->ir_set->erst_size);
 
 		xhci_update_erst_dequeue(xhci, ir, true);
@@ -2333,7 +2333,7 @@ void xhci_add_interrupter(struct xhci_hcd *xhci, unsigned int intr_num)
 
 	/* set ERST count with the number of entries in the segment table */
 	erst_size = readl(&ir->ir_set->erst_size);
-	erst_size &= ERST_SIZE_MASK;
+	erst_size &= ~ERST_SIZE_MASK;
 	erst_size |= ir->event_ring->num_segs;
 	writel(erst_size, &ir->ir_set->erst_size);
 

drivers/usb/host/xhci.h

@@ -251,8 +251,8 @@ struct xhci_intr_reg {
 #define ER_IRQ_COUNTER_MASK	(0xffff << 16)
 
 /* erst_size bitmasks */
-/* Preserve bits 16:31 of erst_size */
-#define	ERST_SIZE_MASK		(0xffff << 16)
+/* bits 15:0 - Event Ring Segment Table Size, number of ERST entries */
+#define	ERST_SIZE_MASK		(0xffff)
 
 /* erst_base bitmasks */
 #define ERST_BASE_RSVDP		(GENMASK_ULL(5, 0))