Re: Flash Back -- kernel 2.1.111

Vojtech Pavlik
2002-02-24T22:40:01Z

On Mon, Feb 25, 2002 at 09:25:13AM +1100, Paul Mackerras wrote:

> Vojtech Pavlik writes:
> > On Mon, Feb 25, 2002 at 09:01:06AM +1100, Paul Mackerras wrote:
> > > We have some RS/6000 machines that have two separate PCI buses (two
> > > host bridges) that run at 33MHz and 50MHz respectively. Fortunately
> > > we also get a device tree from the firmware that tells us this.
> >
> > I really wonder why the 50 MHz one doesn't run at 66 MHz, and what
>
> Apparently the rationale is that you can put more slots on the bus
> if you run it at 50MHz than you can at 66MHz.

I see. That makes sense.

> > happens if you plug in a 66MHz non-capable card to the 50 MHz bus.
>
> The bus speed drops to 33MHz.

Interesting. I'd expect 25 myself ... then we'll definitely need two
clock values in struct pci_bus - because the hi-speed one isn't always a
double the low one - as shown by your example.

--
Vojtech Pavlik
SuSE Labs