From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gw1.transmode.se (gw1.transmode.se [195.58.98.146]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 1B96EB6FFC for ; Fri, 1 Jun 2012 08:33:45 +1000 (EST) In-Reply-To: <4FC7EDD5.8090302@freescale.com> References: <1338363814-19565-1-git-send-email-Joakim.Tjernlund@transmode.se> <6F7E3816-E71B-466A-9C6F-9928E1CFD7B1@digitaldans.com> <10126984030.20120530140826@abatron.ch> <13517672561.20120531113057@abatron.ch> <4FC7AEC9.5050203@freescale.com> <4FC7E606.1070205@freescale.com> <4FC7EDD5.8090302@freescale.com> Subject: Re: [RFC] [PATCH] powerpc: Add MSR_DE to MSR_KERNEL To: Scott Wood Message-ID: From: Joakim Tjernlund Date: Fri, 1 Jun 2012 00:33:41 +0200 MIME-Version: 1.0 Content-type: text/plain; charset=US-ASCII Cc: linuxppc-dev@ozlabs.org, Dan Malek , Bob Cochran , Support List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Scott Wood wrote on 2012/06/01 00:16:53: > > On 05/31/2012 05:14 PM, Joakim Tjernlund wrote: > > Scott Wood wrote on 2012/05/31 23:43:34: > >> > >> On 05/31/2012 04:38 PM, Joakim Tjernlund wrote: > >>> Scott Wood wrote on 2012/05/31 19:47:53: > >>>> > >>>> On 05/31/2012 04:56 AM, Joakim Tjernlund wrote: > >>>>> Abatron Support wrote on 2012/05/31 11:30:57: > >>>>>> > >>>>>> > >>>>>>> Abatron Support wrote on 2012/05/30 14:08:26: > >>>>>>>> > >>>>>>>>>> I have tested this briefly with BDI2000 on P2010(e500) and > >>>>>>>>>> it works for me. I don't know if there are any bad side effects, > >>>>>>>>>> therfore > >>>>>>>>>> this RFC. > >>>>>>>> > >>>>>>>>> We used to have MSR_DE surrounded by CONFIG_something > >>>>>>>>> to ensure it wasn't set under normal operation. IIRC, if MSR_DE > >>>>>>>>> is set, you will have problems with software debuggers that > >>>>>>>>> utilize the the debugging registers in the chip itself. You only want > >>>>>>>>> to force this to be set when using the BDI, not at other times. > >>>>>>>> > >>>>>>>> This MSR_DE is also of interest and used for software debuggers that > >>>>>>>> make use of the debug registers. Only if MSR_DE is set then debug > >>>>>>>> interrupts are generated. If a debug event leads to a debug interrupt > >>>>>>>> handled by a software debugger or if it leads to a debug halt handled > >>>>>>>> by a JTAG tool is selected with DBCR0_EDM / DBCR0_IDM. > >>>>>>>> > >>>>>>>> The "e500 Core Family Reference Manual" chapter "Chapter 8 > >>>>>>>> Debug Support" explains in detail the effect of MSR_DE. > >>>>>> > >>>>>>> So what is the verdict on this? I don't buy into Dan argument without some > >>>>>>> hard data. > >>>>>> > >>>>>> What I tried to mention is that handling the MSR_DE correct is not only > >>>>>> an emulator (JTAG debugger) requirement. Also a software debugger may > >>>>>> depend on a correct handled MSR_DE bit. > >>>>> > >>>>> Yes, that made sense to me too. How would SW debuggers work if the kernel keeps > >>>>> turning off MSR_DE first chance it gets? > >>>> > >>>> The kernel selectively enables MSR_DE when it wants to debug. I'm not > >>>> sure if anything will be bothered by leaving it on all the time. This > >>>> is something we need for virtualization as well, so a hypervisor can > >>>> debug the guest. > >>> > >>> hmm, I read that as you as in favour of the patch? > >> > >> I'd want some confirmation that it doesn't break anything, and that > >> there aren't any other places that need MSR_DE that this doesn't cover, > >> but in general yes. > > > > Then you need to test drive the patch :) > > I was thinking more along the lines of someone who's more familiar with > the relevant parts of the code confirming that it's really OK, not just > testing that it doesn't blow up in my face. Still needs a test run, just throw it in :)