On Tue, Dec 04, 2007 at 01:14:43PM +1100, Benjamin Herrenschmidt wrote: > > .../... (snip scary bunch of errata) > > > - "FEr PCI-#4" (Detailed by Application Note AN-84): > > > > [This isn't strictly a coherency issue but having coherency enabled > > exacerbates the problem.] Basically, the bridge can let the cpu read > > a pci device's registers before all of the data the PCI devices has > > written has actually made it to memory. This and the fact that the > > device's write data may be stuck in the PCI Slave Write Buffer > > (which isn't checked for coherency), the cpu can get stale data. > > > > There are no plans to fix that erratum. > > So if I understand correctly, there's no plan to fix a major PCI spec > violation which prevent any kind of reliable implementation whatsoever ?
That's just for that particular part (e.g., 64360). Newer parts like the 64460 have it fixed. > > So, the answer depends on what part & what rev of the part you have > > (e.g., the pegasos doesn't use the MPSC and apparently has the other > > issues worked around so it can turn on coherency but the prpmc2800 > > doesn't so it needs coherency off). > > > > BTW, I haven't forgotten the inherent bug you described when coherency > > is off (/me too lazy to find link to the email) but AFAIK I've never run > > into it. However, if I turn on coherency and stress the PCI bus, it > > hangs (I can't even look at memory thru a bdi). > > Well, as it is today, the "classic" MMU code cannot deal with !coherent. > The entire linear mapping is always mapped cacheable with BATs, so stuff > may be brought into the cache at any time, potentially polluting DMA > data. > > Dealing with that would be hard. It might be possible by using G on the > entire linear mapping like we do on 4xx (yuck), and/or by not using > D-BATs (the kernel will blow up in various areas without I-BATs). Hrm, I didn't realize it was in such bad shape. I'll have to take a closer look. Mark _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
