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

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Message-ID: <20100623135946.GA30526@redhat.com>
Date:	Wed, 23 Jun 2010 16:59:47 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...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 Wed, Jun 23, 2010 at 04:59:11PM +0300, Avi Kivity wrote:
> On 06/10/2010 06:22 PM, Michael S. Tsirkin wrote:
>> virtio-pci resets the device at startup by writing to the status
>> register, but this does not clear the pci config space,
>> specifically msi enable status which affects register
>> layout.
>>
>> This breaks things like kdump when they try to use e.g. virtio-blk.
>>
>> Fix by forcing msi off at startup. Since pci.c already has
>> a routine to do this, we export and use it instead of duplicating code.
>>
>>    
>
> Why doesn't a device reset result in msi being cleared?

This is not a standard function reset. This is virtio specific
command. So it only clears virtio registers.

> Shouldn't a reset be equivalent to power cycling?

If we did this, driver would need to restore registers
such as BAR etc.

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