usb: hcd: Revert 306c54d: Try MSI interrupts on PCI devices

Customers have been reporting that the I/O is radically being
slowed down to HPE virtual USB ILO served DVD images during installation.

Lots of investigation by the Red Hat lab has found that the issue is
because MSI edge interrupts do not work properly for these
ILO USB devices.
We start fast and then drop to polling mode and its unusable.

The issue exists currently upstream on 5.13 as tested by Red Hat,
and reverting the mentioned patch corrects this upstream.

David Jeffery has this explanation:

The problem with the patch turning on MSI appears to be that the ehci
driver (and possibly other usb controller types too) wasn't written to
support edge-triggered interrupts.
The ehci_irq routine appears to be written in such a way that it will
be racy with multiple interrupt source bits.
With a level-triggered interrupt, it gets called another time and cleans
up other interrupt sources.
But with MSI edge, the interrupt state staying high results in no
new interrupt and ehci has to run based on polling.

static irqreturn_t ehci_irq (struct usb_hcd *hcd)
{
...
        status = ehci_readl(ehci, &ehci->regs->status);

        /* e.g. cardbus physical eject */
        if (status == ~(u32) 0) {
                ehci_dbg (ehci, "device removed\n");
                goto dead;
        }

        /*
         * We don't use STS_FLR, but some controllers don't like it to
         * remain on, so mask it out along with the other status bits.
         */
        masked_status = status & (INTR_MASK | STS_FLR);

        /* Shared IRQ? */
        if (!masked_status || unlikely(ehci->rh_state == EHCI_RH_HALTED)) {
                spin_unlock_irqrestore(&ehci->lock, flags);
                return IRQ_NONE;
        }

        /* clear (just) interrupts */
        ehci_writel(ehci, masked_status, &ehci->regs->status);
...

ehci_irq() reads the interrupt status register and then writes the active
interrupt-related bits back out to ack the interrupt cause.
But with an edge interrupt, this is racy as another source of interrupt
could be raised by ehci between the read and the write reaching the
hardware.
e.g.  If STS_IAA was set during the initial read, but some other bit like
STS_INT gets raised by the hardware between the read and the write to the
interrupt status register, the interrupt signal state won't drop.
The interrupt state says high, and since it is now edged triggered with
MSI, no new invocation of the interrupt handler gets triggered.

Suggested-by: David Jeffery <djeffery@redhat.com>
Suggested-by: Alexandros Panagiotou <apanagio@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Laurence Oberman <loberman@redhat.com>
Fixes: 306c54d PCI: Disable MSI for
Pericom PCIe-USB adapter

drivers/usb/core/hcd-pci.c

@@ -195,21 +195,20 @@ int usb_hcd_pci_probe(struct pci_dev *dev, const struct pci_device_id *id,
 	 * make sure irq setup is not touched for xhci in generic hcd code
 	 */
 	if ((driver->flags & HCD_MASK) < HCD_USB3) {
-		retval = pci_alloc_irq_vectors(dev, 1, 1, PCI_IRQ_LEGACY | PCI_IRQ_MSI);
-		if (retval < 0) {
+		if (!dev->irq) {
 			dev_err(&dev->dev,
 			"Found HC with no IRQ. Check BIOS/PCI %s setup!\n",
 				pci_name(dev));
 			retval = -ENODEV;
 			goto disable_pci;
 		}
-		hcd_irq = pci_irq_vector(dev, 0);
+		hcd_irq = dev->irq;
 	}
 
 	hcd = usb_create_hcd(driver, &dev->dev, pci_name(dev));
 	if (!hcd) {
 		retval = -ENOMEM;
-		goto free_irq_vectors;
+		goto disable_pci;
 	}
 
 	hcd->amd_resume_bug = (usb_hcd_amd_remote_wakeup_quirk(dev) &&
@@ -288,9 +287,6 @@ int usb_hcd_pci_probe(struct pci_dev *dev, const struct pci_device_id *id,
 
 put_hcd:
 	usb_put_hcd(hcd);
-free_irq_vectors:
-	if ((driver->flags & HCD_MASK) < HCD_USB3)
-		pci_free_irq_vectors(dev);
 disable_pci:
 	pci_disable_device(dev);
 	dev_err(&dev->dev, "init %s fail, %d\n", pci_name(dev), retval);
@@ -352,8 +348,6 @@ void usb_hcd_pci_remove(struct pci_dev *dev)
 		up_read(&companions_rwsem);
 	}
 	usb_put_hcd(hcd);
-	if ((hcd_driver_flags & HCD_MASK) < HCD_USB3)
-		pci_free_irq_vectors(dev);
 	pci_disable_device(dev);
 }
 EXPORT_SYMBOL_GPL(usb_hcd_pci_remove);
@@ -465,7 +459,7 @@ static int suspend_common(struct device *dev, bool do_wakeup)
 	 * synchronized here.
 	 */
 	if (!hcd->msix_enabled)
-		synchronize_irq(pci_irq_vector(pci_dev, 0));
+		synchronize_irq(pci_dev->irq);
 
 	/* Downstream ports from this root hub should already be quiesced, so
 	 * there will be no DMA activity.  Now we can shut down the upstream