Re: [Qemu-devel] [RFC 0/9] generate dynamic _CRS for motherboard resources

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 18 Feb 2014 23:04:13 +0100
Laszlo Ersek <lersek@redhat.com> wrote:

> On 02/18/14 17:36, Igor Mammedov wrote:
> > On Mon, 17 Feb 2014 09:32:35 +0100
> > Gerd Hoffmann <kraxel@redhat.com> wrote:
> > 
> >> On So, 2014-02-16 at 17:53 +0200, Michael S. Tsirkin wrote:
> >>> On Fri, Feb 07, 2014 at 01:51:27PM +0100, Igor Mammedov wrote:
> >>>> Since introduction of PCIHP, it became problematic to
> >>>> punch hole in PCI0._CRS statically since PCI hotplug
> >>>> region size became runtime changeable.
> >>>
> >>> What makes it runtime changeable?
> >>
> >> machine type.  q35 / piix map them at different locations.
> >>
> >> Also we might want to this also for devices which are
> >> runtime-configurable (isa-debugcon, pvpanic, ...).
> > I'd convert simple devices that conditionally enabled at
> > startup time, from static definition + patching into
> > completely dynamically generated when device present.
> > For example pvpanic falls in to this category.
> > 
> > That would result in smaller ACPI tables guest has to deal with.
> 
> I could be mistaken, but AFAIR this caused the windows device manager to
> pop up in windows? Ie. if you have a windows guest and cold-boot it
> twice, once with the device present (generated into ACPI) and once with
> the device absent (not generated into ACPI), then you get hardware
> changes. Whereas, if the device is always present and you only patch
> _STA, then windows doesn't perceive it as a hw change.

Is is irrelevant whether device is statically or dynamically created,
user will face the same issue and has a choice to install driver or tell
windows to ignore device forever.

> Do I recall it right?...
Device manager pop-ups only once when new device is added to install driver.
If later, the device in the same location with the same id appears/disappears,
Device manager handles it silently.

> 
> You could argue that "a new device indeed warrants a device manager
> popup", but esp. for isa-debugcon and pvpanic, you might want to enable
> those opportunistically, without triggering a new hw dialog. Pvpanic
> triggering the device manager was exactly what drew frowns, for its
> original implementation. IIRC.
the above applies to these cases as well, i.e. if you install driver for
it then there won't be any pop-ups later. If there is no driver
(which is the case) one needs to tell to Device manager to ignore
this device, and then there shouldn't be an additional pop-ups later.

> Anyway pls. feel free to ignore this comment, it just crossed my mind.
> (And of course it's not related to your series.)
> 
> Thanks
> Laszlo
>