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

[Ani Sinha]

>>> 
>>> Yes. So if there's no _EJx then it's reasonable to assume you can't
>>> isolate the slot, and so no hot-plug will happen either.
>> 
>> Where are you getting that?
> 
> It's well known. For example, the pci hot-plug specification, version
> 1.1, states:
> 
> 1.6 Asssumptions
> 
> ...
> 
> 1.6.2 Orderly Removal and Insertion
> 
> ...
> 
> Furthermore, PCI add-in cards are not generally designed to be connected to a 
> slot that
> has power applied. Therefore, the operating-system vendor and Platform vendor 
> define a
> sequence of user actions and system behavior that guarantees that power is 
> always
> removed from a slot before a card is inserted.
> 
> Inserting or removing an add-in card without following the proper sequence 
> leads to
> unpredictable results, including data corruption, abnormal termination of the 
> operating
> system, or damage to card or Platform hardware. Unless otherwise stated, it 
> is assumed
> throughout the remainder of this specification that the user always follows 
> the proper
> removal and insertion sequence.
> 
> ...
> 
> 
> 2.1 System Components
> 
> ...
> 
> The physical
> insertion or removal must not occur until the system software has:
> • Quiesced any operating system services or drivers using the add-in card
> • Isolated and powered down the slot
> • Indicated to the user that it is ready
> If an add-in card is inserted or removed without following the proper 
> sequence, this is
> considered an improper operation and error conditions and other unexpected 
> events are
> possible, including data corruption and hardware damage.
> 
> and so on.


What does all of this got to so with ACPI hot plug spec which I showed you 
where it clearly says that availability of EJ0 is optional? How are we 
violating the spec? I also gave evidence of Linux detecting it at runtime and 
Windows also seems to allow it.

> 
> 
>> This isn’t true. “_SUN” is used to detect the slot unique number.
> 
> That's just enumeration.
> 
>> Windows does allow hot plugging on the bridge on which EJ0 has been turned 
>> off.
> 
> Given no real or virtual hardware that does that, there's no guarantee
> that I can see that it will keep supporting that in future versions.

You do not know that. I gave evidence that we are not violating the spec.

If RedHat had not moved to q35 and they had come up with this patch for i440fx, 
would you have given this much biased pushback? I seriously doubt it.