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Commit 0b605572 authored by David Jeffery's avatar David Jeffery Committed by Greg Kroah-Hartman
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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: 306c54d0 ("usb: hcd: Try MSI interrupts on PCI devices")
Tested-by: default avatarLaurence Oberman <loberman@redhat.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarDavid Jeffery <djeffery@redhat.com>
Link: https://lore.kernel.org/r/20210715213744.GA44506@redhat


Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1b7f56fb
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