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Date: Mon, 17 Jan 2011 17:20:01 +0100
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: [Qemu-devel] Re: [PATCH 8/8] ahci: fix !msi interrupts
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To: Alexander Graf <agraf@suse.de>
Cc: Kevin Wolf <kwolf@redhat.com>, Joerg Roedel <Joerg.Roedel@amd.com>, Sebastian Herbszt <herbszt@gmx.de>, qemu-devel Developers <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>

On 2011-01-17 17:04, Alexander Graf wrote:
> Jan Kiszka wrote:
>> On 2011-01-17 17:00, Alexander Graf wrote:
>>   
>>> Jan Kiszka wrote:
>>>     
>>>> On 2010-12-20 22:13, Alexander Graf wrote:
>>>>   
>>>>       
>>>>> When not using MSI, receiving an interrupt while the interrupt line is active
>>>>> pulses the interrupt line. Without this, guests don't realize that a new
>>>>> interrupt occured.
>>>>>     
>>>>>         
>>>> This doesn't look OK. The device model should look at the currently used
>>>> mode and switch between edge and level triggering accordingly. As it
>>>> appears like this is what it already does, this change may just paper
>>>> over the real issue.
>>>>   
>>>>       
>>> Well, I have this internal abstraction to make edge and level triggered
>>> interrupt triggering easier. irq_lower is a simple nop for the edge case.
>>>
>>>     
>>
>> I'm concerned about the artificial edge you generate for the level
>> triggered case. That's not like real hw behaves. If you need it,
>> something else might still be broken.
>>   
> 
> Hrm. So worst case we generate a spurious interrupt?
> 

Worse might also be that unknown issue that force you to inject an IRQ
here. We don't know. That's probably worst.

Jan

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