Re: [Qemu-devel] [PATCH 0/5] PCI hotplug fixes/cleanup

[Alex Williamson]

On Tue, 2012-04-10 at 22:36 +0300, Michael S. Tsirkin wrote:
> On Tue, Apr 10, 2012 at 12:29:09PM -0600, Alex Williamson wrote:
> > I never really intended the power state bitmap to be for power
> > management of any sort, I was trying to support this kind of event flow:
> > 
> > http://www.microsoft.com/china/whdc/system/pnppwr/hotadd/hotplugpci.mspx#EYH
> > 
> > Hot-add:
> >  - Generate SCI
> >  - _Lxx/_Exx method determines which slots to Notify
> >  - _STA method for slots indicates device present
> >  - _PS0 requests slot turned on
> >  - _STA method reports device present & enabled
> > 
> > Hot-remove:
> >  - Generate SCI
> >  - _Lxx/_Exx method determines which slots to Notify
> >  - _PS3 powers off slot
> >  - _EJ0 ejects device
> >  - _STA verifies success
> > 
> > _STA is generated using the "present" and "power" registers and _PSx
> > methods directly manipulate "power".  We could then have some kind of
> > "info pcislot" command that allows querying slot state.  Maybe there's
> > even an opportunity for unpowered slot surprise removal.  In effect, the
> > "power" register tracks the "actual" state vs the "requested" state, but
> > if it's controlled by _PSx, it seems better to not try to do a
> > translation.
> > 
> > Are there better models or event flows we should be aiming for?  Thanks,
> > 
> > Alex
> 
> You already said exactly this and both me and Marcelo responded, no?

Sorry, difficult to try to summarize a reply to a weekend+ of
conversation, is this better?

On Sun, 2012-04-08 at 02:13 -0300, Marcelo Tosatti wrote:
On Wed, Apr 04, 2012 at 11:51:00PM -0600, Alex Williamson wrote:
> 
> What problem are you trying to address by doing so?

I'm trying to come up with a model that provides better event life
cycle, clear register ownership, and facilitates features like the event
flow in the msft link above.  We can get away with asking the guest to
do extra device checks on slots, but it's a workaround for a broken
model.

> What is the need for power control? Clearly there is no advantage in    
> powering down a virtual device.

In combination with the "present" register it allows emulating more _STA
states.

On Sun, 2012-04-08 at 10:15 +0300, Michael S. Tsirkin wrote:
On Sun, Apr 08, 2012 at 02:13:00AM -0300, Marcelo Tosatti wrote:
> > What is the need for power control? Clearly there is no advantage in    
> > powering down a virtual device.
> 
> There probably are for an assigned device?

That was not my intention

[Skipping the rest since it's all headed in the direction of using the
power register to do some kind of chipset/device power control]

If there was some decision or direction provided by the rest of the
thread, I missed it, please restate.  Thanks,

Alex