On 4/29/24 09:05, Alan Stern wrote:
On Mon, Apr 29, 2024 at 08:40:10AM -0700, Guenter Roeck wrote:Testing ohci functionality with qemu's pci-ohci emulation often results in ohci interface stalls, resulting in hung task timeouts. The problem is caused by lost interrupts between the emulation and the Linux kernel code. Additional interrupts raised while the ohci interrupt handler in Linux is running and before the handler clears the interrupt status are not handled. The fix for a similar problem in ehci suggests that the problem is likely caused by edge-triggered MSI interrupts. See commit 0b60557230ad ("usb: ehci: Prevent missed ehci interrupts with edge-triggered MSI") for details. Ensure that the ohci interrupt code handles all pending interrupts before returning to solve the problem. Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx> Cc: David Laight <David.Laight@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Fixes: 306c54d0edb6 ("usb: hcd: Try MSI interrupts on PCI devices") Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> --- v3: Check if any interrupts are pending before reading intrenable Add 'Cc: stable@xxxxxxxxxxxxxxx' v2: Only repeat if the interface is still active Note that I did not apply Alan's Reviewed-by: tag since I was not sure if that was appropriate after the code change.I'm not too confident that the guess about all interrupt bits normally being off is correct, but in any case the extra test won't hurt.
OHCI_INTR_RHSC and OHCI_INTR_SF are often set but disabled while the system starts, but afterwards it is mostly 0 during normal operation, i.e., while there are no interface state changes.
Reviewed-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Guenter, if you want to work on a patch to cache the interrupt-enable value in the driver, feel free to do it. I have too much other stuff going on to spend any significant time on ohci-hcd.
Unfortunately I am in the same situation. Also, I am not sure if doing that would really be worth the trouble. Guenter
