Re: [PATCH V2] Add a new PIIX option to control PCI hot unplugging of devices on non-root buses

[Igor Mammedow]

On Fri, 15 May 2020 12:13:53 +0000
Ani Sinha <address@hidden> wrote:

> > On May 14, 2020, at 1:13 AM, Igor Mammedov <address@hidden>
> > wrote: 
> >> 
> >>   
> >>> Will following hack work for you?
> >>> possible permutations
> >>> 1) ACPI hotplug everywhere
> >>> -global PIIX4_PM.acpi-pci-hotplug=on -global
> >>> PIIX4_PM.acpi-pci-hotplug-with-bridge-support=on -device
> >>> pci-bridge,chassis_nr=1,shpc=doesnt_matter -device
> >>> e1000,bus=pci.1,addr=01,id=netdev1 
> >>> 
> >>> 2) No hotplug at all
> >>> -global PIIX4_PM.acpi-pci-hotplug=off -global
> >>> PIIX4_PM.acpi-pci-hotplug-with-bridge-support=on -device
> >>> pci-bridge,chassis_nr=1,shpc=off -device
> >>> e1000,bus=pci.1,addr=01,id=netdev1
> >>> 
> >>> -global PIIX4_PM.acpi-pci-hotplug=off -global
> >>> PIIX4_PM.acpi-pci-hotplug-with-bridge-support=off -device
> >>> pci-bridge,chassis_nr=1,shpc=doesnt_matter  -device
> >>> e1000,bus=pci.1,addr=01,id=netdev1    
> >> 
> >> Given that my patch is not acceptable, I’d prefer the following in
> >> the order of preference:
> >> 
> >> (a) Have an option to disable hot ejection of PCI-PCI bridge so
> >> that Windows does not even show this HW in the “safely remove HW”
> >> option. If we can do this then from OS perspective the GUI options
> >> will be same as what is available with PCIE/q35 - none of the
> >> devices will be hot ejectable if the hot plug option is turned off
> >> from the PCIE slots where devices are plugged into. I looked at
> >> the code. It seems to manipulate ACPI tables of the empty slots of
> >> the root bus where no devices are attached (see comment "/* add
> >> hotplug slots for non present devices */ “). For cold plugged
> >> bridges, it recurses down to scan the slots of the bridge. Is it
> >> possible to disable hot plug for the slot to which the bridge is
> >> attached?  
> > 
> > I don't think it's possible to have per slot hotplug on
> > conventional PCI hardware. it's per bridge property.  
> 
> We add the AMLs per empty slot though. When the pic bridge is
> attached, we do nothing, just recurse into the bridge slots. That is
> what I was asking, if it was possible to just disable the AMLs or use
> some tricks to say that this particular slot is not hotpluggable. I
> am not sure why Windows is trying to eject the PCI bridge and
> failing. Maybe something related to this comment?
> 
> 
> /* When hotplug for bridges is enabled, bridges are
>                               
>          * described in ACPI separately (see build_pci_bus_end).
>                                       
>          * In this case they aren't themselves hot-pluggable.
>                                       
>          * Hotplugged bridges *are* hot-pluggable.
> */

thinking some more on this topic, it seems that with ACPI hotplug we
already have implicit non-hotpluggble slot (slot with bridge) while
the rest are staying hotpluggable.

So my question is: if it's acceptable to add 'PCIDevice::hotpluggable"
property to all PCI devices so that user / libvirt could set it to
false in case they do not want coldplugged device be considered as
hotpluggable? (this way other devices could be treated the same way as
bridges)

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