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


From: Isaku Yamahata
Subject: [Qemu-devel] Re: [PATCH v6 07/12] pcie/hotplug: introduce pushing attention button command
Date: Thu, 21 Oct 2010 18:41:12 +0900
User-agent: Mutt/1.5.19 (2009-01-05)

On Thu, Oct 21, 2010 at 10:02:37AM +0200, Michael S. Tsirkin wrote:
> On Thu, Oct 21, 2010 at 12:46:33PM +0900, Isaku Yamahata wrote:
> > On Wed, Oct 20, 2010 at 12:00:11PM +0200, Michael S. Tsirkin wrote:
> > > On Wed, Oct 20, 2010 at 05:18:56PM +0900, Isaku Yamahata wrote:
> > > > glue pcie_push_attention_button command.
> > > > 
> > > > Signed-off-by: Isaku Yamahata <address@hidden>
> > > 
> > > So as a high level command, I think we need to
> > > think about how to tie this into pci_add/pci_del.
> > > Right?
> > 
> > Maybe or maybe not.
> > I'm not sure it's a good idea to tie it to pci_add/pci_del
> > in the first place.
> > The specification says only that pushing the button is just to
> > initiate the hot-plug operation. It means only a notification.
> > The spec says nothing about the concrete action from OS when
> > the button is pushed. It's up to OS.
> > 
> > For example.
> > OS may start to probe the slot.
> > OS may start to quiescence the device.
> > OS is allowed to ignore the notification. 
> > OS may propagate the notification to the management software,
> > and it would pop up the dialog to the user for further operation.
> > 
> 
> pci_add/pci_del really behave in the same way. There's no way to force
> the OS to respond. We only use ACPI for now, but for express I expect
> standard interfaces will work better long term.

The current qemu pci hot plug requires guest OS intervention as you said.
On the other hand, The express hot plug doesn't requires the intervention.
pci_add/pci_del for express simply populates/deletes PCIDvice
(+ interrupt). No guest OS intervention. It really corresponds to physical
insertion/removal of the pcie card into/from the slot.

Probably I don't understand what you mean by "tie it to pci_add/pci_del".
The command shouldn't be express specific, but more generic?
or something else?
-- 
yamahata



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