Re: [Xen-devel] [RFC] Disable xen platform device when it is not needed.

[Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>]

On Thu, 19 Feb 2009 09:53:54 +0000
Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:

> On 19/02/2009 09:39, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:
> 
> >> I will create the patch to add "xen_platform_pci" option in guest
> >> config file to disable xen platform device.
> >> 
> >>     xen_platform_pci=0: Disable xen platform device.
> >>     xen_platform_pci=1: Enable xen platform device. (default)
> > 
> > I still might veto this. I don't really want the platform device I/O ports
> > scattered elsewhere for this rather frivolous reason.
> 
> Actually it's okay, you can alias the 'platform_flags' byte of the ioport
> BAR to fixed byte port 0x10. There's a handler for that already in
> xen_platform.c (platform_fixed_ioport_{read,write}1). That's the only port
> that hvmloader/rombios cares about.
> 
> Hvmloader/rombios can then always use fixed single-byte ioport 0x10. This is
> actually better since the code is simpler and also rombios accesses that
> port on S3 suspend/resume, at which point an OS could have relocated the
> xen_platform ioport BAR! Using a fixed port is therefore safer.
> 
> Notice that I said you must *alias* this ioport byte. You cannot remove it
> from the xen_platform BAR as old saved guests will rely on it being there,
> and removing it will break their S3. We have to be backward compatible with
> the Xen-3.3 virtual hardware interface for saved guests.
> 
> So, no veto after all!

I will create the patch as follows.

- Alias the 'platform_flags' byte of the ioport BAR to fixed byte port
  0x10, and don't remove existing 'platform_flags' byte.

- Change guest firmware to use new fixed byte port 0x10.

- Add "xen_platform_pci" option in guest config file.

    xen_platform_pci=0: Disable xen platform device.
    xen_platform_pci=1: Enable xen platform device. (default)

Thanks,
--
Yuji Shimada


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