Re: pci express switch driver

[Rajesh Shah <rajesh.shah@intel.com>]

On Wed, Nov 03, 2004 at 05:52:00PM -0800, Sadik, Pallathu wrote:
> Dely, Rajesh and Greg,
> 
>   Why special care is needed for hot-plugging the upstream port?
> As I understand, even if hot-plug signals are provided on the upstream
> port of a switch/endpoint, the generated events gets consumed by
> the downstream port of the root complex/switch  where this card is plugged.
> Hence, the mechanism to handle hot-plugging of the upstream port of
> a switch should be same as hot-plugging of the downstream port of the root
> port.
> 
When you hot-insert the (upstream port of the) 2nd switch, it may 
already have some devices connected to it (downstream). Also, 
the switch _may_ contain hot-pluggable slots (that doesn't
appear to be the case with your motherboard). Someone needs to 
collect resource requirements, program non-conflicting values 
in the end devices and the summed up resource values in the 
switch. This is not an issue during boot, since the system 
firmware has done this already. Also, the hot-added switch 
may contain IO-APICs (as it does in your case). These need 
to be added too. Current hotplug drivers don't have the
code to support this.

> > 
> > shpchp is used to hot-plug PCI or PCI-X devices.  Both 
> > drivers can run on the same system.
> 
>  As I mentioned above, we are planning to use two switches.
> Do I still need the shpchp in this case?
> 
Your switch contains an SHPC controller, so you do need this
driver to hot-plug PCI/PCI-X devices under the switch. However, 
your motherboard doesn't appear to support this.

>    The PCIe hotplug protocol specifies that, when a device is
> in D1, D2 or D3hot state, the hot-plug controller generates
> a wakeup event (PM_PME) instead of an interrupt. Please see

Hmm... I thought you said the motherboard does not support
hotplug of IO devices (no attention button/indicator...). 
What are you trying to do here? Put the switch and all
devices under it to a low-power state and then initiate
a hot-plug operation on an IO device?

> Is there a way to figure out whether the motherboard
> supports ACPI tables for PCIe hotplug in the above
> fashion? Is it possible to see it from the ACPI
> tables that I can get using 'acpidump' command? If it is
> not supported, is there a way I can add them?

Yes, you can dump your ACPI tables, but changing them
to support ACPI based hot-plug is non-trivial. Plus,
just updating your DSDT may not be enough, hardware
support may be needed. 

Rajesh


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