linux-kernel - Re: [PATCH for-2.6.35] virtio-pci: disable msi at startup

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Message-ID: <4C2229DB.6060706@redhat.com>
Date:	Wed, 23 Jun 2010 18:35:55 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	virtualization@...ts.linux-foundation.org,
	Anthony Liguori <aliguori@...ibm.com>,
	linux-pci@...r.kernel.org, Matt Carlson <mcarlson@...adcom.com>,
	linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Bjorn Helgaas <bjorn.helgaas@...com>
Subject: Re: [PATCH for-2.6.35] virtio-pci: disable msi at startup

On 06/23/2010 06:26 PM, Michael S. Tsirkin wrote:
>
>
>>>
>>>        
>>>>>> Shouldn't a reset be equivalent to power cycling?
>>>>>>
>>>>>>
>>>>>>              
>>>>> If we did this, driver would need to restore registers
>>>>> such as BAR etc.
>>>>>
>>>>>
>>>>>            
>>>> We could save/restore the registers we care about.
>>>>
>>>>          
>>> It seems easier to clear registers we care about.
>>>        
>> We know the registers we care about, we don't know the ones we don't.
>>      
> If/when we use more registers, we can update driver to clear them on start.
>    

The kdump kernel may not load drivers for those extra devices.

>> I'm talking about FLRing all cards, not just those you want to use.
>>      
> reset using FLR/PM is complex because of the need to save/restore
> config space. Doing this on a crashing kernel sounds scary.
>    

Well, you only need to save/restore for the devices you use.  The rest 
you reset and forget.

I don't really see why copying some config space is crazy.

>>>     It's also too late
>>> now: changing behaviour will break old drivers.
>>>
>>>        
>> Why?  the FLR is triggered by the guest kernel, so all drivers will be
>> aware it was FLRed.
>>      
> Not for FLR. Too late to reset on PA write.
>
>    

What's PA write?

-- 
error compiling committee.c: too many arguments to function

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