Re: [PATCH] Remove CPU_FTR_NEED_COHERENT for 7448.

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2007-05-03 at 11:13 -0500, Jon Loeliger wrote:
> On Thu, 2007-05-03 at 05:17, Adrian Cox wrote:
> > On Wed, 2007-05-02 at 16:34 -0500, Jon Loeliger wrote: 
> > > From: James.Yang <James.Yang@freescale.com>
> > > 
> > > Remove CPU_FTR_NEED_COHERENT for MPC7448 (and single-core MPC86xx).
> > > This prevents needlessly setting M=1 when not SMP.
> > 
> > There may be side effects to removing this. Most of the 74xx processors
> > had this flag added because of the L2 prefetch bug (erratum #16 on the
> > 7447A). I see that bug is missing from the 7448 errata.
> > 
> > The problem is that many 32-bit PowerPC machines needed
> > CPU_FTR_NEED_COHERENT set for a second reason: compatibility with the
> > cache in the MPC107. This was handled by CPU_FTR_COMMON in cputable.h
> > before the L2 prefetch bug was known.  There may be other host bridges
> > that cache, but nobody will have noticed because all the CPUs had
> > CPU_FTR_NEED_COHERENT set already.
> 
> Adrian,
> 
> Yes, you are correct and your concern is valid.  However,
> this case is still being handled by CONFIG_MPC10X_BRIDGE
> to deal with the MPC106/MPC107/etc north bridges.

I still maintain it should be a runtime thing tho :-)

Ben.