Re: [PATCH 4/4] ACPI PCI slot detection driver

[Gary Hade <garyhade@us.ibm.com>]

Hi Alex/Kenji-san,

Time for my 2 cents.

On Wed, Mar 12, 2008 at 09:24:10PM -0600, Alex Chiang wrote:
> Hi Kenji-san,
> 
> * Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>:
> > Hi Alex-san,
> >
> >> On my machine, it is legal to evaluate S1F0._SUN independent of
> >> S1F0._STA because L001._INI has already been evaluated.
> >> It would be helpful to know what Fujitsu's namespace looks like.
> >> If Fujitsu slot objects contain _STA and _INI, then I agree with
> >> Kenji-san -- I definitely need to check _STA before evaluating
> >> _SUN.
> >
> > Thank you for explanation. Maybe I understood the summary of
> > implementation of HP firmware. But how to use or where to put _INI
> > method in the ACPI namespace never becomes reasonable reason why
> > your driver may ignore _STA before evaluating _SUN.
> >
> >> But in any case, I think both HP and Fujitsu firmware are doing
> >> legal things -- neither firmware is breaking the spec.
> >
> > My understanding of your explanation so far is:
> >
> > - evaluating _SUN without checking _STA doesn't cause problem,
> >  from the view point of HP's implementation.
> > - some IBM machine is doing same as HP
> >
> > I never think those are reasonable reasons why ignoring _STA
> > before evaluating _SUN is legal. Am I missing something?
> 
> I think the piece that I did not explain clearly is that the spec
> does not require checking _STA immediately before _SUN. The spec
> says: 
> 
> 	- you must check _STA before calling _INI
Agreed. 

> 	- _INI must be called to initialize _SUN
Based on my review of ACPI spec 3.0b I would add:
  1. For a specific device that has only _STA and _SUN methods,
     _SUN can be run and it's results can be trusted irrespective
     of the _STA return value.
  2. For a specific device that has _STA, _INI, and _SUN methods,
     _SUN can be run and it's results can be trusted even if
    _INI is not run because the device is absent.  If the device
    is present and _INI is run then _SUN cannot be run until
    after _INI is run.

  See ACPI spec 3.0b "6.1.8 _SUN (Slot User Number)" which
  says nothing about a required presence of the device.

> 	- _INI is called once, when the table is loaded
Agreed.

> 
> On HP's implementation, we do obey those rules. We call _INI on
> the PCI bridge during boot, which then initializes the children
> SxFy objects. From that point on, it is legal for us to call
> _SUN.
> 
> The other issue is that the spec does not specify the *semantics*
> of _STA. P/IBM firmware engineers think _STA should indicate card
> presence, 

I checked this on the IBM x3850 and it appears to be true.  I 
instrumented register_slot() in drivers/pci/hotplug/acpiphp_glue.c
to print _STA and _SUN returns and got the following results with
slot 1 (PCI-X) populated, slot 2 (PCI-X) vacant, slot 3 (PCIe) vacant,
slot 4 (PCIe) populated, slot 5 (PCIe) vacant, and slot 6 (PCIe)
populated.  When a card is present _STA returns non-zero status
for all functions, otherwise it returns zero.  None of the SxFy
devices have an _INI method.

acpiphp: ACPI Hot Plug PCI Controller Driver version: 0.5
acpiphp_glue: found PCI host-bus bridge with hot-pluggable slots
acpiphp_glue: register_slot: \_SB_.VP02.S1F0 sta=0 sun=1
acpiphp_glue: found ACPI PCI Hotplug slot 1 at PCI 0000:02:01
acpiphp: Slot [1] registered
acpiphp_glue: register_slot: \_SB_.VP02.S1F1 sta=0 sun=1
acpiphp_glue: register_slot: \_SB_.VP02.S1F2 sta=0 sun=1
acpiphp_glue: register_slot: \_SB_.VP02.S1F3 sta=0 sun=1
acpiphp_glue: register_slot: \_SB_.VP02.S1F4 sta=0 sun=1
acpiphp_glue: register_slot: \_SB_.VP02.S1F5 sta=0 sun=1
acpiphp_glue: register_slot: \_SB_.VP02.S1F6 sta=0 sun=1
acpiphp_glue: register_slot: \_SB_.VP02.S1F7 sta=0 sun=1
acpiphp_glue: found PCI host-bus bridge with hot-pluggable slots
acpiphp_glue: register_slot: \_SB_.VP03.S2F0 sta=f sun=2
acpiphp_glue: found ACPI PCI Hotplug slot 2 at PCI 0000:06:01
acpiphp: Slot [2] registered
acpiphp_glue: register_slot: \_SB_.VP03.S2F1 sta=f sun=2
acpiphp_glue: register_slot: \_SB_.VP03.S2F2 sta=f sun=2
acpiphp_glue: register_slot: \_SB_.VP03.S2F3 sta=f sun=2
acpiphp_glue: register_slot: \_SB_.VP03.S2F4 sta=f sun=2
acpiphp_glue: register_slot: \_SB_.VP03.S2F5 sta=f sun=2
acpiphp_glue: register_slot: \_SB_.VP03.S2F6 sta=f sun=2
acpiphp_glue: register_slot: \_SB_.VP03.S2F7 sta=f sun=2
acpiphp_glue: found PCI-to-PCI bridge at PCI 0000:0a:00.0
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F0 sta=0 sun=3
acpiphp_glue: found ACPI PCI Hotplug slot 3 at PCI 0000:0b:00
acpiphp: Slot [3] registered
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F1 sta=0 sun=3
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F2 sta=0 sun=3
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F3 sta=0 sun=3
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F4 sta=0 sun=3
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F5 sta=0 sun=3
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F6 sta=0 sun=3
acpiphp_glue: register_slot: \_SB_.VP04.CALG.E3F7 sta=0 sun=3
acpiphp_glue: found PCI-to-PCI bridge at PCI 0000:0f:00.0
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F0 sta=f sun=4
acpiphp_glue: found ACPI PCI Hotplug slot 4 at PCI 0000:10:00
acpiphp: Slot [4] registered
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F1 sta=f sun=4
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F2 sta=f sun=4
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F3 sta=f sun=4
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F4 sta=f sun=4
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F5 sta=f sun=4
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F6 sta=f sun=4
acpiphp_glue: register_slot: \_SB_.VP05.CALG.E4F7 sta=f sun=4
acpiphp_glue: found PCI-to-PCI bridge at PCI 0000:14:00.0
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F0 sta=0 sun=5
acpiphp_glue: found ACPI PCI Hotplug slot 5 at PCI 0000:15:00
acpiphp: Slot [5] registered
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F1 sta=0 sun=5
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F2 sta=0 sun=5
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F3 sta=0 sun=5
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F4 sta=0 sun=5
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F5 sta=0 sun=5
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F6 sta=0 sun=5
acpiphp_glue: register_slot: \_SB_.VP06.CALG.E5F7 sta=0 sun=5
acpiphp_glue: found PCI-to-PCI bridge at PCI 0000:19:00.0
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F0 sta=f sun=6
acpiphp_glue: found ACPI PCI Hotplug slot 6 at PCI 0000:1a:00
acpiphp: Slot [6] registered
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F1 sta=f sun=6
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F2 sta=f sun=6
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F3 sta=f sun=6
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F4 sta=f sun=6
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F5 sta=f sun=6
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F6 sta=f sun=6
acpiphp_glue: register_slot: \_SB_.VP07.CALG.E6F7 sta=f sun=6
acpiphp_glue: Bus 0000:1a has 1 slot
acpiphp_glue: Bus 0000:15 has 1 slot
acpiphp_glue: Bus 0000:10 has 1 slot
acpiphp_glue: Bus 0000:0b has 1 slot
acpiphp_glue: Bus 0000:06 has 1 slot
acpiphp_glue: Bus 0000:02 has 1 slot
acpiphp_glue: Total 6 slots

> but Fujitsu firmware engineers think _STA should
> indicate slot presence.
> 
> I don't think either firmware team is incorrect -- it is simply
> the case that the specification was not precise enough, to the
> point where separate teams following the same spec came up with
> implementations with different behaviors and different semantics.
> 
> I believe that we both have compliant, legal firmware.
> 
> >> If one list is shorter than the other, then that should be the
> >> list to put in the kernel, and the default behavior should be
> >> "majority rule".
> >
> > I don't want to consider "majority rule" before I understand why
> > ignoring _STA is legal.
> 
> On HP and IBM machines, it *is* legal because we *did* call _STA,
> then _INI, then _SUN. That is one interpretation of the spec.
> 
> On Fujitsu machines, the semantics of _STA are different, and it
> is not legal to ignore _STA. That is another interpretation of
> the spec.

I am not convinced that this a correct interpretation.  I believe
that the ACPI spec indicates that it is legal to call _SUN and
trust it's results no matter what _STA returns.  I believe the
only constraint on running _SUN is that it be run after _INI is run
if _INI exists for the same device and _STA for that device
indicates that it should be run.

Gary

-- 
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503  IBM T/L: 775-4503
garyhade@us.ibm.com
http://www.ibm.com/linux/ltc