RE: [PATCH] powerpc/fsl: Add support for pci(e) machine check exception on E500MC / E5500

[Hongtao Jia]

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, September 30, 2014 2:36 AM
> To: Guenter Roeck
> Cc: Benjamin Herrenschmidt; Paul Mackerras; Michael Ellerman; linuxppc-
> dev@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Jojy G Varghese;
> Guenter Roeck; Jia Hongtao-B38951
> Subject: Re: [PATCH] powerpc/fsl: Add support for pci(e) machine check
> exception on E500MC / E5500
> 
> On Mon, 2014-09-29 at 09:48 -0700, Guenter Roeck wrote:
> > From: Jojy G Varghese <jojyv@xxxxxxxxxxx>
> >
> > For E500MC and E5500, a machine check exception in pci(e) memory space
> > crashes the kernel.
> >
> > Testing shows that the MCAR(U) register is zero on a MC exception for
> > the
> > E5500 core. At the same time, DEAR register has been found to have the
> > address of the faulty load address during an MC exception for this core.
> >
> > This fix changes the current behavior to fixup the result register and
> > instruction pointers in the case of a load operation on a faulty PCI
> > address.
> >
> > The changes are:
> > - Added the hook to pci machine check handing to the e500mc machine
> check
> >   exception handler.
> > - For the E5500 core, load faulting address from SPRN_DEAR register.
> >   As mentioned above, this is necessary because the E5500 core does not
> >   report the fault address in the MCAR register.
> >
> > Cc: Scott Wood <scottwood@xxxxxxxxxxxxx>
> > Signed-off-by: Jojy G Varghese <jojyv@xxxxxxxxxxx> [Guenter Roeck:
> > updated description]
> > Signed-off-by: Guenter Roeck <groeck@xxxxxxxxxxx>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> >  arch/powerpc/kernel/traps.c   | 3 ++-
> >  arch/powerpc/sysdev/fsl_pci.c | 5 +++++
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> > index 0dc43f9..ecb709b 100644
> > --- a/arch/powerpc/kernel/traps.c
> > +++ b/arch/powerpc/kernel/traps.c
> > @@ -494,7 +494,8 @@ int machine_check_e500mc(struct pt_regs *regs)
> >  	int recoverable = 1;
> >
> >  	if (reason & MCSR_LD) {
> > -		recoverable = fsl_rio_mcheck_exception(regs);
> > +		recoverable = fsl_rio_mcheck_exception(regs) ||
> > +			fsl_pci_mcheck_exception(regs);
> >  		if (recoverable == 1)
> >  			goto silent_out;
> >  	}
> > diff --git a/arch/powerpc/sysdev/fsl_pci.c
> > b/arch/powerpc/sysdev/fsl_pci.c index c507767..bdb956b 100644
> > --- a/arch/powerpc/sysdev/fsl_pci.c
> > +++ b/arch/powerpc/sysdev/fsl_pci.c
> > @@ -1021,6 +1021,11 @@ int fsl_pci_mcheck_exception(struct pt_regs
> > *regs)  #endif
> >  	addr += mfspr(SPRN_MCAR);
> >
> > +#ifdef CONFIG_E5500_CPU
> > +	if (mfspr(SPRN_EPCR) & SPRN_EPCR_ICM)
> > +		addr = PFN_PHYS(vmalloc_to_pfn((void *)mfspr(SPRN_DEAR)));
> #endif
> 
> Kconfig tells you what hardware is supported, not what hardware you're
> actually running on.
> 
> Jia Hongtao, do you know anything about this issue?  Is there an erratum?

Sorry for the late response, I just return from my vacation.
I don't know this issue.

> What chips are affected by the the erratum covered by
> <http://patchwork.ozlabs.org/patch/240239/>?

MPC8544, MPC8548, MPC8572 are affected by this erratum.
I checked P4080 which using e500mc and no such erratum is found.

> 
> Can we rely on DEAR or is this just a side effect of likely having taken
> a TLB miss for the address recently?  Perhaps we should use the
> instruction emulation to determine the effective address instead.
> 
> Guenter, is this patch intended to deal with an erratum or are you
> covering up legitimate errors?
> 
> -Scott
> 

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