On Fri, 2013-05-31 at 14:41 +0800, Kevin Hao wrote: > Hi Ben, > > Could you shed some light on this issue? Do we really has the restriction > that we have to pick one bus controller as primary even there is no > ISA bus on the board? I did check the current code and found no code > has a requirement for this. I also searched the archives and but found > nothing useful. :-(
You can just pick the first one as primary... The reason we somewhat need a primary is related to how we handle IO space. We ioremap the IO space of all busses and assign the base of the primary one to a global "_IO_BASE". Then any "port" access is an offset from that which means that non-primary can end up having negative offsets. We fix up all resources, which works fine ... unless drivers do stupid casts and the wrap-around fails. The main reason we did that originally is because we still had a slew of x86 originated HW that would access hard wired IO ports, especially on things like CHRP machines, looking for things like 8259 PIC, legacy kbd controllers, UARTs, etc... at fixed IO port numbers. We still support some of these boxes (though I do wonder how long since somebody last booted a Pegasos) so I'm not quite yet keen on getting rid of that stuff... Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
