Re: [Pcihpd-discuss] what is writing to /sys/bus/pci/slot/<slot_no>/power really supposed to do?

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Oct 01, 2007 at 10:35:57AM -0700, Kristen Carlson Accardi wrote:
> So - here's where we get to interpret.  The spec says that _EJ0 is
> used to "eject" the card.  From the spec:
> 6.3.3 _EJx (Eject)
> These control methods are optional and are supplied for devices that 
> support a software-controlled VCR-style ejection mechanism or that 
> require an action be performed such as isolation of power/data lines 
> before the device can be removed from the system. 
> <snip>
> For hot removal, the device must be immediately ejected when OSPM calls 
> the _EJ0 control method. The _EJ0 control method does not return until 
> ejection is complete. After calling _EJ0, OSPM verifies the
> device no longer exists to determine if the eject succeeded. 
> For _HID devices, OSPM evaluates the _STA method. For _ADR devices, 
> OSPM checks with the bus driver for that device.
> 
> So, when I read this, it seems like if a vendor followed the spec,
> executing _EJ0 would hang until we physically pulled the card out
> of the system, which seems bad.  So, maybe this is why we don't call
> _EJ0?  

I think you've misread it.  Follow the other arm of the 'or':
	"require an action be performed such as isolation of power/data
	lines before the device can be removed from the system."
So I interpret "the eject succeeded" as "power/data lines are isolated"
for PCI cards.

> _PS3 apparently is used to put a device into D3.  By "device" here
> I'm not sure if we are talking about the adapter in the slot, or the
> slot itself.

Slots don't have a D3.  If you're talking about the bus, I guess there's
a B3.  But D is for devices.

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