This is a note to let you know that I've just added the patch titled

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

to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 0b60557230adfdeb8164e0b342ac9cd469a75759 Mon Sep 17 00:00:00 2001

From: David Jeffery djeffery@redhat.com Date: Thu, 15 Jul 2021 17:37:44 -0400 Subject: usb: ehci: Prevent missed ehci interrupts with edge-triggered MSI

When MSI is used by the ehci-hcd driver, it can cause lost interrupts which results in EHCI only continuing to work due to a polling fallback. But the reliance of polling drastically reduces performance of any I/O through EHCI.

Interrupts are lost as the EHCI 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.

Fixes: 306c54d0edb6 ("usb: hcd: Try MSI interrupts on PCI devices") Tested-by: Laurence Oberman loberman@redhat.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Acked-by: Alan Stern stern@rowland.harvard.edu Signed-off-by: David Jeffery djeffery@redhat.com Link: https://lore.kernel.org/r/20210715213744.GA44506@redhat Cc: stable stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/host/ehci-hcd.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c index 36f5bf6a0752..10b0365f3439 100644 --- a/drivers/usb/host/ehci-hcd.c +++ b/drivers/usb/host/ehci-hcd.c @@ -703,24 +703,28 @@ EXPORT_SYMBOL_GPL(ehci_setup); 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 status, current_status, masked_status, pcd_status = 0; + u32 cmd; int bh;

spin_lock(&ehci->lock);

- status = ehci_readl(ehci, &ehci->regs->status); + status = 0; + current_status = ehci_readl(ehci, &ehci->regs->status); +restart:

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

/* * 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;