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

[Ani Sinha]

> 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.                              
                            
         */



> 
> 
>> (b) Failing above, having a global option to disable all hot plug, including 
>> the 32 slots of the root bus would be good. However, this does not give us 
>> the flexibility we have with PCIE (that is, to hot plug a  device, we can 
>> always plug it to a slot with hot plug enabled).
> 
> sounds fine to me, at least it will address problem.
> Can you post a patch to that effect please?
> /It should disable all AML related to hotplug and related hadware code/

I have tried a patch and sent it.