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Sender: Guenter Roeck <groeck7@gmail.com>
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Date: Wed, 24 Apr 2024 15:59:36 -0700
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Subject: Re: [PATCH v2] usb: ohci: Prevent missed ohci interrupts
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Alan Stern <stern@rowland.harvard.edu>
Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
 Gerd Hoffmann <kraxel@redhat.com>
References: <20240424195951.3749388-1-linux@roeck-us.net>
 <0a29cc85-a79e-476d-aae6-0a054aad2e90@rowland.harvard.edu>
 <2024042441-salutary-finishing-f54d@gregkh>
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From: Guenter Roeck <linux@roeck-us.net>
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In-Reply-To: <2024042441-salutary-finishing-f54d@gregkh>
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On 4/24/24 15:49, Greg Kroah-Hartman wrote:
> On Wed, Apr 24, 2024 at 06:30:06PM -0400, Alan Stern wrote:
>> On Wed, Apr 24, 2024 at 12:59:51PM -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>
>>> ---
>>> v2: Only repeat if the interface is still active
>>
>> Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
>>
>> Greg might insist that the patch be CC'ed to stable@vger.kernel.org since
>> it contains a Fixes: tag.
> 
> I'll add that by hand, no worries.

Thanks!

Guenter