Re: [Qemu-devel] [PATCH v2 21/21] q35: add acpi-based pci hotplug.

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 11, 2012 at 11:34:08AM -0400, Jason Baron wrote:
> On Thu, Oct 11, 2012 at 04:46:56PM +0200, Michael S. Tsirkin wrote:
> > On Thu, Oct 11, 2012 at 10:21:22AM -0400, Jason Baron wrote:
> > > On Thu, Oct 11, 2012 at 12:57:06PM +0200, Michael S. Tsirkin wrote:
> > > > On Mon, Oct 08, 2012 at 11:30:39PM -0400, Jason Baron wrote:
> > > > > From: Jason Baron <jbaron@redhat.com>
> > > > > 
> > > > > Add piix style acpi hotplug to q35.
> > > > > 
> > > > > Signed-off-by: Jason Baron <jbaron@redhat.com>
> > > > 
> > > > Something I don't understand here: this only handles hotplug
> > > > of devices behind the root, no?
> > > > Don't we need support for hotplug/hot remove of devices behind
> > > > bridges?
> > > > 
> > > 
> > > Yes, this only handles acpi hotplug of devices behind the root. I'm
> > > trying to reach minimal set of q35 patches that we can build upon. I
> > > think that this patch gives us at least the same functionality as piix
> > > does. (Plus there is pcie hotplug).
> > > 
> > > As you know, I have a proof of concept patch series providing a second
> > > level of hotplug behind bridges. Unfortunately, it was based on the
> > > static acpi tables, before Paolo made the hotplug table generation
> > > dynamic. So it needs quite a bit of re-work. But I know that it should
> > > work :)
> > > 
> > > Thanks,
> > > 
> > > -Jason
> > 
> > Yes. Reason I ask is because q35 is adding bridges by default now.
> > Would it be possible to only add them if requested on command line by user
> > instead? I realize some guests expect devices at specific slots
> > but this does not apply to bridges I think?
> > 
> 
> I just tried out getting rid of the bridges by default.
> 
> So 'lspci' goes from:
> 
> 00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM Controller
> 00:01.0 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:02.0 VGA compatible controller: Cirrus Logic GD 5446
> 00:03.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet Controller (rev 03)
> 00:17.0 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:18.0 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:1c.0 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:1c.1 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:1c.2 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:1c.3 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:1c.4 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:1c.5 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express Root Port 0 (rev 02)
> 00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 92)
> 00:1f.0 ISA bridge: Intel Corporation 82801IB (ICH9) LPC Interface Controller (rev 02)
> 00:1f.2 SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port SATA AHCI Controller (rev 02)
> 00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus Controller (rev 02)
> 03:00.0 PCI bridge: Texas Instruments XIO3130 PCI Express Switch (Upstream) (rev 02)
> 04:00.0 PCI bridge: Texas Instruments XIO3130 PCI Express Switch (Downstream) (rev 01)
> 0c:1c.0 PCI bridge: Digital Equipment Corporation DECchip 21154 (rev 05)
> 0c:1d.0 PCI bridge: Digital Equipment Corporation DECchip 21154 (rev 05)
> 0c:1e.0 PCI bridge: Digital Equipment Corporation DECchip 21154 (rev 05)
> 0c:1f.0 PCI bridge: Digital Equipment Corporation DECchip 21154 (rev 05)
> 
> To:
> 
> 00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM Controller
> 00:01.0 VGA compatible controller: Cirrus Logic GD 5446
> 00:02.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet Controller (rev 03)
> 00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 92)
> 00:1f.0 ISA bridge: Intel Corporation 82801IB (ICH9) LPC Interface Controller (rev 02)
> 00:1f.2 SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port SATA AHCI Controller (rev 02)
> 00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus Controller (rev 02)
> 
> 
> Windows and Linux guests seem fine with either layout. Slots 1-2 are
> specific to my setup. So this is a pretty minimal set.

I guess we can remove the PCI bridge too?

One interesting side effect here is that there are less free pci slots
on root bus now.  I guess at minimum management needs to be taught about
this, and I'm not sure how.

> I think that providing the minimal set of devices is good, since it
> allows the user to configure things as much as possible. So I am in
> favor of this more minimal set. My only hesitation is that we pull out,
> or that I have not included some important piece h/w at a specific slot
> that a guest might need. Thus potentially breaking existing setups.
> Perhaps, that might mean a new machine type in the future, if we've
> messed up?

Yes, that's one solution.

> These devices and slots are pulled from the Intel docs on ICH9 and Q35
> specs. See:
> 
> http://www.intel.com/content/www/us/en/io/io-controller-hub-9-datasheet.html
> 
> Perhaps, Yamahata can comment further on the specific set of bridges?
> 
> > It would also be nice to add comments explaining why
> > specific slots were selected e.g. /* BSD XYZ fails to boot unless ahci is at alow 2 */
> > etc.
> 
> Right, its basically just pulled from the Intel spec as mentioned above.
> 
> > 
> > Also - will adding this code now mean that when adding bridges
> > we'll need to add compatibility code in bios/qemu in the future?
> > 
> 
> I don't think so, but maybe you can elaborate this concern more
> specifically?
> 
> Thanks,
> 
> -Jason

Just this: can same bios work on this interface and the one
you intend for hotplug behind bridge? Or will we need to version
interface?

-- 
MST