diff mbox series

usb: ehci: Prevent missed ehci interrupts with edge-triggered MSI

Message ID 20210714140309.GA27799@redhat
State New
Headers show
Series usb: ehci: Prevent missed ehci interrupts with edge-triggered MSI | expand

Commit Message

David Jeffery July 14, 2021, 2:03 p.m. UTC 
When MSI is used by the ehci driver, it can cause interrupts to be lost which
results in ehci only continuing to work due to its polling fallback.  But the
reliance of polling drasticly reduces performance of any I/O through ehci.

Interrupts are lost as ehci's interrupt handler does not safely handle
edge-triggered interrupts.  It fails to ensure all interrupt status bits are
cleared, which works with level-triggered interrupts but not the 
edge-triggered interrupts typical from using MSI.

To fix this problem, check if the driver may have raced with the hardware
setting additional interrupt status bits and clear status until it is in a
stable state.

Signed-off-by: David Jeffery <djeffery@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
---

This is an alternative to reverting 306c54d0edb6ba94d39877524dddebaad7770cf2
which is the patch that allowed MSI to be used with ehci.

 ehci-hcd.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 36f5bf6a0752..2283205d4b40 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -704,14 +704,18 @@  static irqreturn_t ehci_irq (struct usb_hcd *hcd)
 {
 	struct ehci_hcd		*ehci = hcd_to_ehci (hcd);
 	u32			status, masked_status, pcd_status = 0, cmd;
+	u32			current_status;
 	int			bh;
 
 	spin_lock(&ehci->lock);
 
-	status = ehci_readl(ehci, &ehci->regs->status);
+	status = 0;
 
+	current_status = ehci_readl(ehci, &ehci->regs->status);
+restart:
+	status |= current_status;
 	/* e.g. cardbus physical eject */
-	if (status == ~(u32) 0) {
+	if (current_status == ~(u32) 0) {
 		ehci_dbg (ehci, "device removed\n");
 		goto dead;
 	}
@@ -720,7 +724,7 @@  static irqreturn_t ehci_irq (struct usb_hcd *hcd)
 	 * 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);
+	masked_status = current_status & (INTR_MASK | STS_FLR);
 
 	/* Shared IRQ? */
 	if (!masked_status || unlikely(ehci->rh_state == EHCI_RH_HALTED)) {
@@ -730,6 +734,12 @@  static irqreturn_t ehci_irq (struct usb_hcd *hcd)
 
 	/* clear (just) interrupts */
 	ehci_writel(ehci, masked_status, &ehci->regs->status);
+
+	/* for edge interrupts, don't race with an interrupt bit being raised */
+	current_status = ehci_readl(ehci, &ehci->regs->status);
+	if (current_status & INTR_MASK)
+		goto restart;
+
 	cmd = ehci_readl(ehci, &ehci->regs->command);
 	bh = 0;