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Sender: Guenter Roeck <groeck7@gmail.com>
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Date: Wed, 24 Apr 2024 11:21:54 -0700
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Subject: Re: [PATCH] usb: ohci: Prevent missed ohci interrupts
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
 Gerd Hoffmann <kraxel@redhat.com>
References: <20240424170250.3738037-1-linux@roeck-us.net>
 <57511487-e622-476d-adb2-5dfc725032d4@rowland.harvard.edu>
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From: Guenter Roeck <linux@roeck-us.net>
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In-Reply-To: <57511487-e622-476d-adb2-5dfc725032d4@rowland.harvard.edu>
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On 4/24/24 11:15, Alan Stern wrote:
> On Wed, Apr 24, 2024 at 10:02:50AM -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@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;
> 
> If we take the repeat, we don't want to return IRQ_NOTMINE by accident.  To
> prevent this, we should check that ohci->rh_state != OHCI_RH_HALTED before
> re-reading ints and jumping back.
> 
> (If rh_state _is_ OHCI_RH_HALTED, it means the device is supposedly stopped
> and disabled for generating further interrupt requests, so we shouldn't
> need to worry about any outstanding intrstatus bits still set.)
> 

Makes sense. I'll send v2.

Thanks,
Guenter