[RFC] [PATCH] powerpc: Add MSR_DE to MSR_KERNEL

[Zang Roy-R61911]

> -----Original Message-----
> From: linuxppc-dev-bounces+tie-fei.zang=freescale.com at lists.ozlabs.org
> [mailto:linuxppc-dev-bounces+tie-fei.zang=freescale.com at lists.ozlabs.org]
> On Behalf Of Joakim Tjernlund
> Sent: Friday, June 01, 2012 6:36 AM
> To: Wood Scott-B07421
> Cc: linuxppc-dev at ozlabs.org; Dan Malek; Bob Cochran; Support
> Subject: Re: [RFC] [PATCH] powerpc: Add MSR_DE to MSR_KERNEL
> 
> Scott Wood <scottwood at freescale.com> wrote on 2012/06/01 00:16:53:
> >
> > On 05/31/2012 05:14 PM, Joakim Tjernlund wrote:
> > > Scott Wood <scottwood at freescale.com> wrote on 2012/05/31 23:43:34:
> > >>
> > >> On 05/31/2012 04:38 PM, Joakim Tjernlund wrote:
> > >>> Scott Wood <scottwood at freescale.com> wrote on 2012/05/31 19:47:53:
> > >>>>
> > >>>> On 05/31/2012 04:56 AM, Joakim Tjernlund wrote:
> > >>>>> Abatron Support <support at abatron.ch> wrote on 2012/05/31 11:30:57:
> > >>>>>>
> > >>>>>>
> > >>>>>>> Abatron Support <support at abatron.ch> 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.
> 
> It just occurred to me that you guys have this already in your Linux SDK so
> it can't be that bad.
No. MSR_DE is ONLY added when using CW debug in SDK.
Roy