xhci: Limit time spent with xHC interrupts disabled during bus resume

Current xhci bus resume implementation prevents xHC host from generating
interrupts during high-speed USB 2 and super-speed USB 3 bus resume.

Only reason to disable interrupts during bus resume would be to prevent
the interrupt handler from interfering with the resume process of USB 2
ports.

Host initiated resume of USB 2 ports is done in two stages.

The xhci driver first transitions the port from 'U3' to 'Resume' state,
then wait in Resume for 20ms, and finally moves port to U0 state.
xhci driver can't prevent interrupts by keeping the xhci spinlock
due to this 20ms sleep.

Limit interrupt disabling to the USB 2 port resume case only.
resuming USB 2 ports in bus resume is only done in special cases where
USB 2 ports had to be forced to suspend during bus suspend.

The current way of preventing interrupts by clearing the 'Interrupt
Enable' (INTE) bit in USBCMD register won't prevent the Interrupter
registers 'Interrupt Pending' (IP), 'Event Handler Busy' (EHB) and
USBSTS register Event Interrupt (EINT) bits from being set.

New interrupts can't be issued before those bits are properly clered.

Disable interrupts by clearing the interrupter register 'Interrupt
Enable' (IE) bit instead. This way IP, EHB and INTE won't be set
before IE is enabled again and a new interrupt is triggered.

Reported-by: Devyn Liu <[e-mail]>
Closes: https://lore.kernel.org/linux-usb/[e-mail]/
Cc: [e-mail]
Tested-by: Devyn Liu <[e-mail]>
Signed-off-by: Mathias Nyman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/xhci-hub.c

···
 	int max_ports, port_index;
 	int sret;
 	u32 next_state;
-	u32 temp, portsc;
+	u32 portsc;
 	struct xhci_hub *rhub;
 	struct xhci_port **ports;
+	bool disabled_irq = false;
 
 	rhub = xhci_get_rhub(hcd);
 	ports = rhub->ports;
···
 		return -ESHUTDOWN;
 	}
 
-	/* delay the irqs */
-	temp = readl(&xhci->op_regs->command);
-	temp &= ~CMD_EIE;
-	writel(temp, &xhci->op_regs->command);
-
 	/* bus specific resume for ports we suspended at bus_suspend */
-	if (hcd->speed >= HCD_USB3)
+	if (hcd->speed >= HCD_USB3) {
 		next_state = XDEV_U0;
-	else
+	} else {
 		next_state = XDEV_RESUME;
-
+		if (bus_state->bus_suspended) {
+			/*
+			 * prevent port event interrupts from interfering
+			 * with usb2 port resume process
+			 */
+			xhci_disable_interrupter(xhci->interrupters[0]);
+			disabled_irq = true;
+		}
+	}
 	port_index = max_ports;
 	while (port_index--) {
 		portsc = readl(ports[port_index]->addr);
···
 	(void) readl(&xhci->op_regs->command);
 
 	bus_state->next_statechange = jiffies + msecs_to_jiffies(5);
-	/* re-enable irqs */
-	temp = readl(&xhci->op_regs->command);
-	temp |= CMD_EIE;
-	writel(temp, &xhci->op_regs->command);
-	temp = readl(&xhci->op_regs->command);
+	/* re-enable interrupter */
+	if (disabled_irq)
+		xhci_enable_interrupter(xhci->interrupters[0]);
 
 	spin_unlock_irqrestore(&xhci->lock, flags);
 	return 0;

drivers/usb/host/xhci.c

···
 		xhci_info(xhci, "Fault detected\n");
 }
 
-static int xhci_enable_interrupter(struct xhci_interrupter *ir)
+int xhci_enable_interrupter(struct xhci_interrupter *ir)
 {
 	u32 iman;
 
···
 	return 0;
 }
 
-static int xhci_disable_interrupter(struct xhci_interrupter *ir)
+int xhci_disable_interrupter(struct xhci_interrupter *ir)
 {
 	u32 iman;
 

drivers/usb/host/xhci.h

···
 		struct usb_tt *tt, gfp_t mem_flags);
 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);
 
 /* xHCI ring, segment, TRB, and TD functions */
 dma_addr_t xhci_trb_virt_to_dma(struct xhci_segment *seg, union xhci_trb *trb);