[Fwd: Re: OpenFirmware and interrupt-map]

Tarl Neustaedter Tarl.Neustaedter at sun.com
Tue Feb 3 18:52:00 CET 2004

[ re-send, hopefully having fixed subscription issues ]

> Interesting.   The observation that powerful firmware eventually
> becomes an OS so you might as well use an OS, seems true :)

One benefit we're hoping for is to not have to write multiple drivers
every time we go to a new technology (e.g., infiniband). Right now,
we're facing the possibility of needing to write a Solaris driver,
a Linux driver, an IEEE-1275 FCode driver, and a real-mode BIOS
driver. All for one technology, and with the probability of having
to repeat for the next i/o technology to come along, since we are
going forward with both SPARC and Opteron-based systems.

With LinuxBIOS, it looks like it should be possible to re-use
the Linux driver in the PROM. If so, it would mean that a new
platform based on a particular i/o technology could contain the
drivers for that particular technology (e.g., for Infiniband,
IPoIB and SRP drivers), and not have to worry about option ROMs.

If it saves us several engineer-years in development, that's good.

> The one problem with using Linux so far has been size constraints.

I can believe it. My task right now is to determine if LinuxBIOS
is feasible, and if so, at what size. We have some flexibility in that
we design our own boards, so if we  can justify a large PROM, we
could get it in. Better if we can fit it in a 1MB prom, however.

> I have recently found some kernel patches that start to shrink the
> Linux kernel by allowing you to compile out unnecessary pieces so
> I about ready to make a foray into using Linux as our bootloader
> again.   But until I have squeezed a lot of the size bloat out I won't
> be convinced it is the way to go.

I'll be [very] interested in this.

> The location where option roms come into play in the pc world are
> scsi adapters, raid controllers, and video.  For scsi adapters and
> raid controllers every case I have looked at the linux drivers are
> good enough that you don't need the option roms.  Video drivers are
> still problematic.
> How has sun coped with getting video drivers for high end video
> cards.  I know Apple seems to have succeeded in working with
> NVIDIA.  I suspect that is with open firmware side but I don't know.

A Sun video card comes with an OpenFirmware driver. That means that
Sun has either designed and built the card itself, or has signed a
deal with a vendor to re-sell their video cards after writing a driver
and putting it on the option ROM. The usual arrangement is that this
driver is still intellectual property of the video card vendor, so
that he can maintain secrecy on how to use his card. Don't know why.

To some extent, cards can be moved between Suns, Apples, IBM PowerPC
platforms and some HP systems, all of which use the IEEE 1275 standard.
Each implementation has slightly diverged from each other, and now that
the 1275 committee isn't meeting any more, quirks are tending cause
further divergence.

Note that an openfirmware video driver isn't particularly feature-rich.
It primarily provides a dumb scrolling ascii text window. There are
definitions for fancier capabilities (cursor positioning, color,
character insertion), but I've never seen anyone use them - or even
know if these capabilities work in our drivers.

       Tarl Neustaedter, CST Firmware, Sun Microsystems

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