Mark A. Greer wrote: > On Tue, Dec 04, 2007 at 07:52:50AM +1100, Benjamin Herrenschmidt wrote: > >>> #address-cells = <1>; >>> + #size-cells = <1>; >>> + model = "Katana-Qp"; /* Default */ >>> + compatible = "emerson,Katana-Qp"; >>> + coherency-off; >>> + >>> >> What do that mean (coherency-off) ? >> >> Somebody is trying again to use a 74xx with non cache coherent DMA ? >> > > Hi Ben. > > I suspect Andrei got that from the prpmc2800 dts which I made so I'll > jump in. (BTW, this is the same debate we have every year or two. :) > > By looking at the dts, that board has an mv64460 which has a couple > issues when it comes to coherency (depending on the rev of the chip). > > One is about not being able to use DCBST instructions with coherency on > and the other is about limiting the length of one of the traces (which > at least one board manufacturer that I know of refuses to implement). > The first one is supposed to be fixed by rev A1 of the part and the second > is supposed to be fixed by rev B0 of the part. I don't know what rev(s) > are on the board(s) Andrei is using. If its B0 or later, in theory, the > part should work with coherency on. > > Andrei, have you tested with coherency on? > Yes, I tested it with "coherency on", but it didn't work.
I checked chip revisions on all boards I have and they all are >= mv64_4_60 B0. Emerson team working on U-Boot for KatanaQP (David Jenkins copied in cc) notified that they have newer firmware version which makes "coherency on" functional. At the moment I have no more details on it, but I'll investigate this issue soon and let you know all the details. > -- > [snip errata] > -- > > 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). > > Mark > Thanks, Andrei. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
