usb: xhci: remove '0' write to write-1-to-clear register

xHCI specification 1.2, section 5.5.2.1.
Interrupt Pending bit is RW1C (Write-1-to-clear), which means that
writing '0' to is has no effect and is removed.

The Interrupt Pending (IP) bit is cleared at the start of interrupt
handling; xhci_clear_interrupt_pending(). This could theoretically
cause a new interrupt to be issued before the xhci driver reaches
the interrupter disable functions.
To address this, the IP bit is read after Interrupt Enable is
disabled, and a debug message is issued if the IP bit is still set.

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/20250515135621.335595-18-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 10 insertions, 9 deletions

diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
index 486347776cb2..92bb84f8132a 100644
--- a/drivers/usb/host/xhci-hub.c
+++ b/drivers/usb/host/xhci-hub.c
@@ -1907,7 +1907,7 @@ int xhci_bus_resume(struct usb_hcd *hcd)
 			 * prevent port event interrupts from interfering
 			 * with usb2 port resume process
 			 */
-			xhci_disable_interrupter(xhci->interrupters[0]);
+			xhci_disable_interrupter(xhci, xhci->interrupters[0]);
 			disabled_irq = true;
 		}
 	}
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 4a4410f7978f..1cae4ec6c7e9 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3166,7 +3166,7 @@ void xhci_skip_sec_intr_events(struct xhci_hcd *xhci,
 	dma_addr_t deq;
 
 	/* disable irq, ack pending interrupt and ack all pending events */
-	xhci_disable_interrupter(ir);
+	xhci_disable_interrupter(xhci, ir);
 
 	/* last acked event trb is in erdp reg  */
 	erdp_reg = xhci_read_64(xhci, &ir->ir_set->erst_dequeue);
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 8cdb1a01a3ed..6c4bbabc3a70 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -331,7 +331,6 @@ int xhci_enable_interrupter(struct xhci_interrupter *ir)
 		return -EINVAL;
 
 	iman = readl(&ir->ir_set->irq_pending);
-	iman &= ~IMAN_IP;
 	iman |= IMAN_IE;
 	writel(iman, &ir->ir_set->irq_pending);
 
@@ -340,7 +339,7 @@ int xhci_enable_interrupter(struct xhci_interrupter *ir)
 	return 0;
 }
 
-int xhci_disable_interrupter(struct xhci_interrupter *ir)
+int xhci_disable_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir)
 {
 	u32 iman;
 
@@ -348,11 +347,13 @@ int xhci_disable_interrupter(struct xhci_interrupter *ir)
 		return -EINVAL;
 
 	iman = readl(&ir->ir_set->irq_pending);
-	iman &= ~IMAN_IP;
 	iman &= ~IMAN_IE;
 	writel(iman, &ir->ir_set->irq_pending);
 
-	readl(&ir->ir_set->irq_pending);
+	iman = readl(&ir->ir_set->irq_pending);
+	if (iman & IMAN_IP)
+		xhci_dbg(xhci, "%s: Interrupt pending\n", __func__);
+
 	return 0;
 }
 
@@ -754,7 +755,7 @@ void xhci_stop(struct usb_hcd *hcd)
 			"// Disabling event ring interrupts");
 	temp = readl(&xhci->op_regs->status);
 	writel((temp & ~0x1fff) | STS_EINT, &xhci->op_regs->status);
-	xhci_disable_interrupter(ir);
+	xhci_disable_interrupter(xhci, ir);
 
 	xhci_dbg_trace(xhci, trace_xhci_dbg_init, "cleaning up memory");
 	xhci_mem_cleanup(xhci);
@@ -1189,7 +1190,7 @@ int xhci_resume(struct xhci_hcd *xhci, bool power_lost, bool is_auto_resume)
 		xhci_dbg(xhci, "// Disabling event ring interrupts\n");
 		temp = readl(&xhci->op_regs->status);
 		writel((temp & ~0x1fff) | STS_EINT, &xhci->op_regs->status);
-		xhci_disable_interrupter(xhci->interrupters[0]);
+		xhci_disable_interrupter(xhci, xhci->interrupters[0]);
 
 		xhci_dbg(xhci, "cleaning up memory\n");
 		xhci_mem_cleanup(xhci);
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 28c4ad7534c1..fc6b97add7fa 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1900,7 +1900,7 @@ int xhci_alloc_tt_info(struct xhci_hcd *xhci,
 int xhci_set_interrupter_moderation(struct xhci_interrupter *ir,
 				    u32 imod_interval);
 int xhci_enable_interrupter(struct xhci_interrupter *ir);
-int xhci_disable_interrupter(struct xhci_interrupter *ir);
+int xhci_disable_interrupter(struct xhci_hcd *xhci, struct xhci_interrupter *ir);
 
 /* xHCI ring, segment, TRB, and TD functions */
 dma_addr_t xhci_trb_virt_to_dma(struct xhci_segment *seg, union xhci_trb *trb);