Re: Hot Plug I/O Node spec 0.2.1

[David Brownell <david-b@pacbell.net>]

Interesting ...

> IO Node Hot Plug Design Notes
> ==============> 
> Revision 0.2.1
> by Hiroshi Aono (h-aono@ap.jp.nec.com)

    [ deletia ] 

> 1.2. IO node
> 
> Expected system layout:
> 
>                            +---+   +---+
>                            |CPU|...|CPU|
>                            +---+   +---+
>                              |       |
>                            +-----------+
>                            |    PS     |
>                            +-----------+
>                           -> |       | <- Hot-pluggable
>                            +---+   +---+
>                            |ION|...|ION|
>                            +---+   +---+
> 
>       PS: PortSwitch
>       ION: IO Node
> 
>                        Figure 1 Hot-pluggable System
>                        ----------------------------
> 
> An IO node can be hot-pluggable between the PS (Port Switch) and IO
> node. An IO node consists of IO bridges, interrupt controllers, some PCI
> buses, many PCI slots and so on.
> 
>                IONode
>             +-----------------------------------------------+    
>             | BRIDGE0                      BRIDGE1   ...... |
>             |+-------------------------+ +---------+        |
>             ||       +-------+         | |         |        |
>             ||       |IOSAPIC|         | |         |        |
>             ||       +-------+         | |         |        |
>             || PCIBUS0  PCIBUS1 .....  | |         |        |
>             ||| --+-- || --+--SLOT     | |         |        |
>             ||| --+-- || --+--SLOT     | |         |        |
>             ||| --+-- || --+-- |       | |         |        |
>             ||| --+-- || --+-- |       | |         |        |
>             ||+-------++-------+       | |         |        |
>             |+-------------------------+ +---------+        |
>             +-----------------------------------------------+
> 
>                           Figure 2 IO Node
>                           ---------------
> 
> The BRIDGE is not only a PCI bridge but also next generation IO bridges
> such as Infiniband, 3GIO and so on.

So presumably you'll be looking at hotplug support for those
other kinds of bridge and device, though perhaps not right
away.  That's good.


> Both hot-plugging and the removal of interfaces between OS and hardware
> is mainly performed by ACPI. When insertion or removal of an IO node, a
> single interrupt (calls SCI) is generated.

Must it work this way -- depending on ACPI?  I know there's a
fair degree of discomfort with the notion of needing to depend
on traditionally flakey BIOS level code.  (I'd make a similar
comment for other BIOS dependencies described in this 0.2.1
draft.)  My understanding is that folk would rather rely on open
hardware specs for the Linux kernel, since it's shown to lead to
more robust and reliable systems.


> 2.1. Domain Resource Manager
> 
> The IO node manager has an interface to communicate with the Domain
> Resource Manager. We will have to decide the details of the interface.

This would be a Linux component I happen not to have heard of.
Is it perhaps an ACPI component?   It'd be good to see a pointer
to this (as well as the ATLAS project you mentioned, and all
the other components referenced here).



> 3.3. Hotplug Filesystem
> 
> We'd like to use the hotplug filesystem. This is for PCI hotplug
> filesystem and we feel this is most suitable for the generic hotplug
> interface. The hotplug filesystem will be used for user interfaces.
> We will improve this to treat a hierarchical structure for describing 
> IO node objects.

So far, nobody else has felt a need for a hotplug filesystem.
It'd be interesting to know the "user interfaces" you're thinking
about, and why a new filesystem might be needed.


> IO node hotplug hierarchical structure will be as follows:
> 
>   --+ ionodeXX
>          + bridgeXX
>              + slotXX
>              + slotXX
>              + pic
>          + bridgeYYY
>              + slotYY
>              + slotYY
>              + pic
>          
> Each node is a directory, and they have following files:
> 
>      o adapter
>      o attention
>      o latch 
>      o power
>      o test
> 
> These files are used for controlling hotplug functions.

Hmm, sounds like maybe the 2.5 "driverfs" is more appropriate
than a "hotplug filesystem".  Is that what you meant?

- Dave




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