Re: pci express switch driver

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

On Fri, Oct 29, 2004 at 09:37:51PM -0700, Greg KH wrote:
> On Sat, Oct 09, 2004 at 07:15:37PM -0700, Sadik, Pallathu wrote:
> > 
> >    Currently, I am working on developing a driver
> > for a PCI express switch that have one upstream and
> > multiple downstream ports with hotplug capability.
> 
> I've waited so long in responding, as I would hope the Intel people I
> know would pipe up.  But they didn't :(
> 
That probably would be me (plus several other who discussed this
with Greg at OLS) :-). Sorry, my mail system seems to be 
screwed up and I never saw the original post.

> Anyway, some other people are currently working on adding this kind of
> functionality to Linux.  But I have no idea when they will release it to
> the public...

What we are working on is ACPI based hot-plug of an IO complex 
rooted on a host bridge or a P2P bridge. If the switch you 
describe looks like a p2p bridge to Linux, what we're working 
on would probably overlap with what you need. We still
need to resolve some ACPI/namespace issues, so we're not quite
ready to send patches yet.

> 
> > However, I am not able to figure out whether these
> > are applicable in the case of a switch. 
> > 
> >   My hardware setup is as follows:
> > 
> > PCI express switch:
> >   As I have mentioned above, the switch is going to
> > have one upstream and multiple downstream ports.
> > The downstream ports have implemented hotpulg feature
> > (Attention indicator, power indicator, attention button,
> > MRL sensor etc). They are capable of generating interrupts
> > on the hotplug events.
> 
What hotplug technology do you plan to use to hotplug the switch 
itself? This is a platform/firmware capability. For example, if
you want to use SHPC based hotplug, there must be an SHPC 
controller north of the switch you want to hotplug. If you
want to support ACPI based hotplug, your firmware has to
describe it in the ACPI namespace, generate the appropriate
notification etc.

Once the switch itself is hotplugged, downstream IO devices 
can be hotplugged using SHPC/PCI-E mechanisms if the switch
has hotplug capabilities. Looks like your switch does
support SHPC/PCI-E hotplug.

> 
> > 1. Do I need to write a driver for this device? I couldn't locate a 
> > driver for PCI to PCI bridge in the linux code and functionally a
> > PCI express switch is not that much different from a PCI bridge.
> 
Since we will be using ACPI based hotplug, we'll be extending
acpiphp. 

> 
> > pci_hotplug, shpchp, pciehp, acpiphp. I experimentally found out
> > that the pci_hotplug module is required for the rest of the modules
> > to load. However, I am not sure which one I should select.
> 
You need to select the ones that your platform hardware and 
firmware supports.

> 
> > As I understand acpiphp is for ACPI based hotplug control and
> > pciehp is for PCI express native hotplug. Is that true? Do I need
> > both of them for the correct operation?
> 
Again, depends on your platform capability. 

Rajesh



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