Re: PCI Hot Plug Operation

[Greg KH <greg@kroah.com>]

On Fri, May 03, 2002 at 11:00:10AM -0500, Bill Bruce wrote:
> My situation:
> 
> The software base is Redhat 7.2. The kernel has been updated to 2.4.9. The
> user-space hot plug files/scripts dated 2002_4_1 from SourceForge have been
> installed.
> 
> I install a PCI card in my system and power it up. It appears on the PCI bus
> (lspci -H1 confirms this).
> 
> There is no driver for this card in the kernel, but according to my reading
> of the hot plug documentation I expect the /sbin/hotplug script to be
> invoked, giving me an opportunity to load a driver. This is not happening.

/sbin/hotplug is not envoked at the first scanning of the PCI bus.  This
might be considered a bug, but as there is no userspace set up at this
point in time, any call out to /sbin/hotplug would not work anyway :)

This will be fixed in 2.5, when we have initramfs working.

> Some rudimentary questions:
> 
> I am assuming the kernel is periodically scanning the PCI bus, looking for
> new devices. Is this correct? If so how often does this happen?

No, this is not happening.

> Do I need to install a driver for my card to make the kernel aware of a
> possible hot pluggable device?

PCI Hotplug only works if you have a PCI Hotplug controller on your
motherboard.  This is usually only on high end servers or cPCI machines.
Do you have such a machine?

If not, you need to manually load the kernel module for your pci device,
sorry, as there are no "hotplug" pci events able to be generated.

I've posted a small module that manually rescans the pci bus and allows
events to be generated if it sees a new device, but this is a bit of a
hack :)  Check the archives if you're interested.

thanks,

greg k-h

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