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Sender: Guenter Roeck <groeck7@gmail.com>
From: Guenter Roeck <linux@roeck-us.net>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Guenter Roeck <linux@roeck-us.net>,
	Gerd Hoffmann <kraxel@redhat.com>
Subject: [PATCH] usb: ohci: Prevent missed ohci interrupts
Date: Wed, 24 Apr 2024 10:02:50 -0700
Message-Id: <20240424170250.3738037-1-linux@roeck-us.net>
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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@redhat.com>
Fixes: 306c54d0edb6 ("usb: hcd: Try MSI interrupts on PCI devices")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/usb/host/ohci-hcd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
index 4f9982ecfb58..4d764eb6c1e5 100644
--- a/drivers/usb/host/ohci-hcd.c
+++ b/drivers/usb/host/ohci-hcd.c
@@ -888,6 +888,7 @@ static irqreturn_t ohci_irq (struct usb_hcd *hcd)
 	/* Check for an all 1's result which is a typical consequence
 	 * of dead, unclocked, or unplugged (CardBus...) devices
 	 */
+again:
 	if (ints == ~(u32)0) {
 		ohci->rh_state = OHCI_RH_HALTED;
 		ohci_dbg (ohci, "device removed!\n");
@@ -982,6 +983,11 @@ static irqreturn_t ohci_irq (struct usb_hcd *hcd)
 	}
 	spin_unlock(&ohci->lock);
 
+	/* repeat until all enabled interrupts are handled */
+	ints = ohci_readl(ohci, &regs->intrstatus);
+	if (ints & ohci_readl(ohci, &regs->intrenable))
+		goto again;
+
 	return IRQ_HANDLED;
 }
 
-- 
2.39.2