Re: [Qemu-devel] Re: [PATCH v6 07/12] pcie/hotplug: introduce pushing attention button command

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

On Mon, Oct 25, 2010 at 12:29:57PM +0900, Isaku Yamahata wrote:
> On Fri, Oct 22, 2010 at 04:38:49PM +0200, Michael S. Tsirkin wrote:
> > On Fri, Oct 22, 2010 at 01:35:47PM +0200, Markus Armbruster wrote:
> > > "Michael S. Tsirkin" <mst@redhat.com> writes:
> > > 
> > > > On Wed, Oct 20, 2010 at 05:18:56PM +0900, Isaku Yamahata wrote:
> > > >> glue pcie_push_attention_button command.
> > > >> 
> > > >> Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
> > > >
> > > > So as a high level command, I think we need to
> > > > think about how to tie this into pci_add/pci_del.
> > > > Right?
> > > [...]
> > > 
> > > Do we have consensus how our set of commands for hot plug should look
> > > like?  We talked about it, but did we reach consensus?  If yes, did we
> > > write it down somewhere?
> > 
> > I think for simple things yes:
> > - command to send hotplug notification to the guest
> > - command to immediately add/remove the device
> > - event to notify about guest ack
> > - way to poll status: did guest ack last command?
> 
> I'm not sure about guest ack. Let me check my understanding.


Your understanding is correct.

> The current qemu pci hot plug has its own hot plug controler,
> PIIX4_PM, which relies on ACPI.
> 
> - command to add the device into the slot
>   This corresponds to physically inserting the device into the slot.
>   - qemu pci hot plug case: device_add/pci_add command.
>     The qemu pci hot plug controller, PIIX4_PM, detects the insertion,
>     then notify the guest OS of the event via ACPI, _L01.
>     The guest OS would start to probe the device.
> 
>   - pci express native hot plug case: device_add/pci_add command.
>     The pcie hot plug controller detects the the insertion,
>     then notify the guest OS of the event via interrupt.
>     The guest OS would start to probe the device.
> 
> - command to remove the device from the slot
>   This corresponds to physically removing the device from the slot.
>   - qemu pci hot plug case: No corresponding command.
>     There is no way to remove the pci card forcibly from the slot.
> 
>   - pci express native hot plug case: device_del/pci_del
>     After the removal of the card, the hot plug controller notifies
>     the guest OS via interrupt.
> 
> - command to send hotplug notification to the guest
>   command to push attention button.
>   This corresponds to pushing the button near the slot.
>   - qemu pci hot plug case: device_del/pci_del command
>     Maybe the button is called an eject button.
>     When the button is pushed, the hot plug controller notifies
>     the guest OS via ACPI, _L01.
>     Then, guest OS reacts the event by calling ACPI \_SB.PCI0.S<n>._EJ0
>     method. It program the hot plug controller to eject the device
>     in the given slot. As a result, the device is removed from the slot.
>     If the guest OS doesn't call _EJ0 (nor programs the controller directly),
>     the device stays there.
>     There is no way to remove the pci card without the guest OS
>     intervention.
> 
>   - pci express native hot plug case:
>     pcie_push_attention_button command with my patch series.
>     The hot plug controller raise the interrupt to the guest OS.
>     There is no specified action from the OS.

Right. So what is suggested is that we have
A. a single command to push the attention button
B. a single command to remove pci card without guest OS interaction
C. a way to interact with the guest
management tools or human monitor will be able to tie A,B,C together
in various interesting ways

What I am also saying is that the same command should be able
to work for pci and express I think.

> - a way to get the slot status
>   new command for QMP/HMP? or enhance info pci?
> 
> - QMP event for qemu to notify the slot status change
>   e.g. when LED status is changed, qmp event will be sent.
> 
> > Existing ones will keep function:
> > - send notification and when acked remove device
> > - add device and send notification
> > These are useful for human monitor but maybe not
> > for management.
> > 
> > 
> > -- 
> > MST
> > 
> 
> -- 
> yamahata