Subject: Re: [PATCH V4] powerpc/85xx: Add machine check handler to fix PCIe erratum on mpc85xx

From: Scott Wood <[email-masked]>
Date: Mon, 4 Mar 2013 17:45:44 -0600

On 03/04/2013 10:16:10 AM, Stuart Yoder wrote:
> On Mon, Mar 4, 2013 at 2:40 AM, Jia Hongtao <[email-masked]> =20
> wrote:
> > A PCIe erratum of mpc85xx may causes a core hang when a link of PCIe
> > goes down. when the link goes down, Non-posted transactions issued
> > via the ATMU requiring completion result in an instruction stall.
> > At the same time a machine-check exception is generated to the core
> > to allow further processing by the handler. We implements the =20
> handler
> > which skips the instruction caused the stall.
>=20
> Can you explain at a high level how just skipping an instruction =20
> solves
> anything?   If you just skip a load/store and continue like nothing is
> wrong, isn't your system possibly in a really bad state.

If the instruction was a load, we probably at least want to fill the =20
destination register with 0xffffffff or similar.

> And if the core is already hung, due to the PCI link going down, isn't
> it too late?   How does skipping help?

Maybe the machine check unhangs the core?

Is there an erratum number for this?

-Scott=