Re: The role of OpenFirmware in arch/powermac

[Andrew Cagney <cagney%tpgi.com.au@localhost>]

Excerpts from mail: 16-Feb-98 Re: The role of OpenFirmwar.. Markus
Illenseer%core.de@localhost (511*)

> > I've been looking at this, and I think I've come to a conclusion.  It seems
> > that it should be possible to move all openfirmware calls to one place in
> > the very beginning of the kernel, or perhaps even in the booter once I
> > figure out what the heck I'm doing wrong with it.

>  I am not sure if I really groke the idea. Currently there is no native
> SCSI driver for my PowerPC-System, hence I am depending on OpenFirmware
> all the time, not only at boot time. I do not have a PowerMac.

Dan,

(Maybe I'm still living in a CHRP dream :-)

As a bit of revision, the openfirmware/chrp model is roughly as follows:

        o       machine boots open-firmware

        o       open-firmware loads kernel image

        o       kernel image uses device-tree to
                determine device drivers that need to be
                loaded.

                NB: If no device driver is available, the OF
                interface to the device can be retained as a
                slow fallback.

                NB: Since the device tree provides a complete
                description of the hardware there shouldn't be
                any need for the driver code to probe the device/
                bus.  Interesting idea this!

        o       If device drivers for all devices are found
                _then_ openfirmware can be unloaded and
                the OF resources reclaimed.

                NB: Of course, one could force an unload if
                the device that wasn't found was, say, a
                sound card :-)

        o       regardless of the state of openfirmware
                the machine also provides a light weight
                `RTAS' (pronunced ratsac?) (run-time
                abstraction services).  These services
                include primatives such as machine halt.

Consequently, the OF calls can't be isolated to the boot code.   Since
the kernel can't unload a staticly linked driver, there will probably
always be at least the text of the OF-driver around.  Of course, if the
kernel could unload such device drivers, ... :-)

        make sense?

                enjoy,
                        Andrew


--

Why is it that my 486 can boot MINIX in less than a second :-^