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Date: Thu, 30 Apr 2009 14:15:26 -0300
From: Marcelo Tosatti <mtosatti@redhat.com>
Message-ID: <20090430171526.GA10638@amt.cnet>
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Subject: [Qemu-devel] Re: questions on default_config_write in hw/pci.c
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, Avi Kivity <avi@redhat.com>, qemu-devel@nongnu.org

On Thu, Apr 30, 2009 at 07:15:08PM +0300, Michael S. Tsirkin wrote:
> Hi,
> I've been looking at hw/pci.c, specifically at how config
> read/write are implemented, and have a couple of questions
> about default_config_write:
> 
> 1. The code at the beginning (if len == 4 ...)
>    seems to only update pci base registers if a dword write 
>    is performed. I think it's legal for the guest to perform 4
>    single-byte writes. Should this be supported?
> 
> 2. The large switch statement at the end of this function
>    uses hard-coded register offsets. Would it make sense
>    to change it to use macros from hw/pci.h?
> 
> 3. Still there I see:
>         switch(d->config[0x0e]) {
>         case 0x00:
>         case 0x80:
>    register 0x0e is header type, which has defined values
>    of 0x00 (device or host bridge), 0x01 (pci to pci bridge) and
>    0x02 (cardbus bridge). What is 0x80 and when is it used?
>    Would it make sense to remove this?

Don't know. Check the PCI spec?

> 4. Still there, there's some handling done for type 1 devices.
>    This support seems imcomplete.
>    Are there any PCI-to-PCI bridges emulated by qemu?
>    Would it make sense to remove this code?


It did work at one point:

http://www.mail-archive.com/kvm-devel@lists.sourceforge.net/msg16647.html