From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from buildserver.ru.mvista.com (unknown [85.21.88.6]) by ozlabs.org (Postfix) with ESMTP id B1DA6DDEBE for ; Wed, 5 Dec 2007 04:28:18 +1100 (EST) Message-ID: <47558E59.4040107@ru.mvista.com> Date: Tue, 04 Dec 2007 20:28:57 +0300 From: Andrei Dolnikov MIME-Version: 1.0 To: "Mark A. Greer" Subject: Re: [PATCH 1/5] PowerPC 74xx: Katana Qp device tree References: <20071129152836.GB13751@ru.mvista.com> <1196715170.13230.228.camel@pasglop> <20071204012329.GA18903@mag.az.mvista.com> In-Reply-To: <20071204012329.GA18903@mag.az.mvista.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: David.Jenkins@emerson.com, linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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.