PCI bridge support with MontaVista

PCI bridge support with MontaVista

[Jeff Studer]

Hello all,

We are in the early stages of a new embedded MPC860T project and we are
looking at using the MontaVista distribution of Linux for the OS.  We need
PCI support but are flexible on what PCI bridge we will use.

What we need to know is what PCI bridges are supported by with this
distribution.  I found some PPC PCI bridge support patches mentioned
online, so I am assuming there may be some PCI bridges that could be
supported by applying a patch, if the support does not yet exist with
MontaVista's distribution.  Are there any cases like this?

I did not see information regarding PCI bridge support on MontaVista's
site, so I am asking here.  We really need to know what is supported so we
can make a choice on what to use.  Any further information would be
helpful, regarding ease of use and cost, or any other personal opinions. I
have worked with the QSpanII with another OS, but we had to write our own
drivers for that.

Thank you for your help,

Jeff Studer


Aquila Technologies Group, Inc.
Albuquerque, NM


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Re: PCI bridge support with MontaVista

[Mark A. Greer]

Jeff Studer wrote:

> Hello all,
>
> We are in the early stages of a new embedded MPC860T project and we are
> looking at using the MontaVista distribution of Linux for the OS.  We need
> PCI support but are flexible on what PCI bridge we will use.
>
> What we need to know is what PCI bridges are supported by with this
> distribution.  I found some PPC PCI bridge support patches mentioned
> online, so I am assuming there may be some PCI bridges that could be
> supported by applying a patch, if the support does not yet exist with
> MontaVista's distribution.  Are there any cases like this?
>
> I did not see information regarding PCI bridge support on MontaVista's
> site, so I am asking here.  We really need to know what is supported so we
> can make a choice on what to use.  Any further information would be
> helpful, regarding ease of use and cost, or any other personal opinions. I
> have worked with the QSpanII with another OS, but we had to write our own
> drivers for that.

Just off the top of my head there are several bridges that are supported, the
Motorola SPS MPC105, MPC106, MPC107 (and MPC824x), the Motorola MCG Raven,
Hawk, Harrier, IBM CPC700 and CPC710, several proprietary bridges, and others
that are in the works.

Since the code already exists for these bridges, working with them
[softwarewise] isn't that much of an issue.  Probably the most important thing
for you would be price & performance.  Unfortunately, I have no idea about the
price and I've never personally gotten around to doing a true apples-to-apples
comparison of the various host bridges & their options.  :(

I'll bet Dan Malek and Matt Porter can provide more insight.

Mark


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Re: PCI bridge support with MontaVista

[Dan Malek]

"Mark A. Greer" wrote:

> Just off the top of my head there are several bridges that are supported, the
> Motorola SPS MPC105, MPC106, MPC107 (and MPC824x), the Motorola MCG Raven,
> Hawk, Harrier, IBM CPC700 and CPC710, several proprietary bridges, and others
> that are in the works.

None of these work on the MPC8xx bus, so they aren't options.

The first thing I have to ask is do you _really_ need a PCI bridge.
If yes, because you have PCI slots and expect any PCI card to work,
I would then strongly suggest looking at something with a real PCI
bridge solution, like the 824x with an integrated, standard PCI
bridge.

If you are building a "closed" embedded solution, the most successful
8xx designs don't use a PCI bridge.  Due to the flexibility of the 8xx
bus, it is much more efficient (lower cost, less software, lower power,
higher performance), to simply configure the 8xx bus or add some trivial
external logic.  This has been done with sound chips, graphics,
additional
uarts, IDE, USB, and so on.  You don't need PCI to attach these devices.

If you really insist on using a PCI bridge with the 8xx, keep in mind
the bridge is only a (small) part of the entire system solution.  The
PCI bridge simply provides the bus translation between the 8xx and the
PCI.
You have to solve the problem of interrupts as well.  The best way is
probably to just connect the PCI INTAs to the MPC8xx external IRQs, then
you need to somehow adapt the software to work.  This has been the
source
of much hacking in the past, without any general solution.  Ensure the
bridge and your system configuration can actually perform PCI bus
mastering
of the 8xx bus, if you need this.  The QSpanII claims to finally be able
to do this, so check it out.  The PCI bridges also claim a large part of
the physical address (usually the upper 2G) and do their own decoding.
I've seen one design that tried to fake a smaller 8xx space with some
external logic, but this never worked due to bus timing problems. I
guess the moral of the story is don't be cute with the design :-).

So, make sure you _really_ need that PCI bridge.  Due to the work of
a few people, the PCI subsystem is very modular and easy to update.
All you may need to add are a few configuration space access functions
and an initialization function (which is always unique to the board
design).  Choose a bridge that has the features you want, connect it
in a very straightforward design, and the software will fall into place
rather easily (maybe :-). I still prefer the no PCI design with
MPC8xx....

Good Luck.


	-- Dan

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