multiple separate pci bridges ...

Sven Luther sven.luther at
Tue Jan 6 18:39:55 EST 2004

On Tue, Jan 06, 2004 at 09:12:06AM +1100, Benjamin Herrenschmidt wrote:
> > Mmm, will look into this. Actually, linux should not write to those, but
> > read access should be ok.
> If the BARs contain address ranges that will confuse linux resource
> management (like RAM location), then you have to hide them completely.

Mmm, will check.

BTW, X has problems with pci config space access. It simply opens the
/proc/bus/pci/<bus>/<dev>.<func> stuff, and is not happy with the

Is the above just a plain ioremap of config space or something such, or
does the reads there use the pci access functions ?

> > Well, i tried ioremapping 0x10000, but without much success
> > (cfg_addr/data is at cf8/cfc, and this magic stuff is at f118/f11c). I
> > just got a sig 11 OOPS, so ...
> I don't fully understand... If you are doing IO cycles, there's no
> ioremapping needed at all at this point, just use the one that is done
> once for the bridge IO space. neither cf8/cfc not f118 look like
> addresses that can be ioremap'ed anyway...

Well, it is f1000cf8/cfc and f100f118/f11c naturally, and the second is
needed to enable a hardware kludge to make the second pci bus look like
agp. I don't really have the details of such, but i need to write to the
f118/f11c before/after each pci access to the second pci bus, as well as
disable the CPU interrupts for doing the access.

> > > just ioremap that in a global once... I do that for a few things in
> > > pmac_feature.c, like the northbridge registers.
> >
> > Yeah, i have seen.
> >
> > > > Also, i had to manually set hose->bus_offset = 0x10, since that didn't
> > > > seem to be set automatically. I don't know why though.
> > >
> > > Why do you need hose->bus_offset ? For indirect_pci ? Well... that's
> >
> > Nope, i checked, and it was trying to read the bus 0x10, while the bus
> > is in reallity 0. That said, if i understood stuff correctly, it should
> > be ok, since type 0 config ignores bus and device, right ?
> Yes. And for type 1, just issue a cycle to (bus - hose->first_busno)

How are the config access functions told that they shall do a type 0 or
1 access ? I have seen there is something in the pci_indirect functions
that do this, but not sure i can do it here.

> > > a kludge, you should rather fix indirect_pci to use first_busno
> > > instead... I don't know where this bus_offset comes from in the first
> > > place, it's defined in pci_controller but not used at all in 2.6...
> >
> > Yeah, nor in 2.4, if my grep is correct. I can't use indirect_pci for
> > the second bus though.
> >
> > > (BTW. You should really work on 2.6, not 2.4...)
> >
> > Ah, yes, but 2.4 means suppoprt for debian-installer. Once that works, i
> > will work on 2.6.x. Also, 2.4 provides me a known working base.
> I still don't like the idea of new dev. beeing done on 2.4...

Well, once i get it working, i will go on to 2.6, promised :))

That said, i was a bit disapointed by 2.6. If you remember, i had some
problems with 2.4, since the second IDE bus uses a different interrupt
than the first one, so i used a kludge in the via-ide driver to make it
work. The 2.6 ide driver has per ide channel setup, but still does get
the primary ide interrupt for the second channel too.

> > This is which bewilders me, the bridge spec speak about type 0 and type
> > 1, and using the last 2 bits for this.
> Yes. Usually, you don't put the last 2 bits of the offsets in cfg_addr,
> you crop that value to the closest 32 bits boundary (or 64 bits in some
> chips), and then you "offset" the cfg_data access.
> For example, for a 8 bits access at an offset of 7, you would use 4
> as the offset in cfg_addr, and then do a 8 bits access at cfg_data + 3

Ok, understand better now.

> > The Marvell Discovery II has (one, two or three) gigabit ethernets
> > included, these do not appear on the pci bus, but need to be programmed
> > directly with the NB registers. On the other hand, the sk98 driver
> > provides driver for various Marvell gigabit ethernet.
> Argh ????? They don't appear on PCI ? What piece of SHIT is this bridge ?

Well, the Discovery II use a internal crossbar switch, and the ethernet
are on the same level as the pci buses. This makes for very efficient
networking i guess, but has problems. In fact, each of these ones has
the same priority as each pci bus.

I believe it should be possible to have each of these appear as an
independent pci bus or something ?

> Really totally insane.

Well, i am no hardware guy, so i cannot make judgement on this, but i
guess there are worse hardware out there.

> I strongly suggest you still match them as PCI devices, eventually using
> the bridge device itself as the match for the driver.... The DMA mapping
> ops are designed to work with PCI anyway.

Mmm. Will have to look into that.

Again, thanks for your help,


Sven Luther

** Sent via the linuxppc-dev mail list. See

More information about the Linuxppc-dev mailing list