[cgl_discussion] RE: [Fwd: hotswap and CGL (fwd)]

Rusty Lynch rusty at linux.co.intel.com
Thu May 1 10:53:39 PDT 2003

On Thu, 2003-05-01 at 06:32, John J Grana wrote:
> Not to put too fine a point on this, but some of the subtle problems with
> the present implementation is starting to show itself.
> Last I read the code, the present CompactPCI hotswap still relied on a PCI
> bus being present on the device being swapped. In the discussion below, it
> mentions a daemon that retrieves hotswap events (good) but then talks about
> a vendor/device id.
> In a cPCI backplane with the actual PCIbus supported, this is not a
> problem. Every board has it's PCI bridge that will respond with a
> vendor/device id.
> Now, fast forward to what is happening today... PICMG 2.16 Packet Switched
> Backplane introduced switched ethernet to the backplane, but "optionally"
> allowed the PCIbus to stay in place. But, the next generation of these
> class of chassis (CompactTCA) has NO PCIbus at all. Ditto for AdvancedTCA.
> I had tried to kick start a thread a while back, asking the question
> "Assuming no PCIbus, what is the best standards method of identifying
> devices in a backplane?". This includes not only hotswapping but boot time
> discovery as well. There were 2 ways proposed. IPMI or Ethernet. There were
> many pros and cons to each method.
> The present 2.5 cpci_hotplug code has come a long way, looks good. But, in
> its present form will only support cPCI systems that have a PCIbus.
> Assuming we (CGL) leave it this way, it is safe to say that both 2.6 Linux
> and CGL do NOT support hotswap in "some" 2.16 systems and not at all on
> CompactTCA and AdvancedTCA.
> Cheers
> John Grana
> jjg at pt.com
Exactly what kind of hotswap is not enabled on non-PCI CompactTCA and

>From what I have seen, these systems either have:

1. a complete compute nodes plugged into a slot, so as far as the kernel
running on this blade is concerned, nothing is different then if the
kernel was running on a normal rack mounted server.  What does hotswap
mean in this case?

2. some kind of special purpose device (like a line card) that will
communicate with other machines via the particular high speed bus in the
backplane (like Gigabit ethernet).  From what I have seen (like with
Gigabit on the backplane), there is nothing to do in the kernel (beyond
what the bus driver is already doing) to support the notion of hotswap.

Maybe you could give a specific example of a device that hotswap is not
supported with an ATCA or CompactTCA?


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