[PATCH RFC] ARM: MPCore v6_early_abort enhancement

[Russell King - ARM Linux]

On Fri, Feb 11, 2011 at 05:53:42PM -0500, George G. Davis wrote:
> Hi,
> 
> On Fri, Feb 11, 2011 at 10:38:44PM +0000, Russell King - ARM Linux wrote:
> > On Sat, Feb 12, 2011 at 12:54:21AM +0300, Valentine Barshak wrote:
> > > SWP instruction sets bit 11 in DFSR, in case of data fault on SMP MPCore.
> > > So v6_early_abort doesn't need erratum 326103 workaround for MPCore.
> > 
> > NAK.  When building a SMP kernel which also supports v6 CPUs, this will
> > cause v6 CPUs to break.
> 
> Since the SWP erratum only affects ARM1136 (UP) processors, how will this
> break ARM11 MPCore (v6) processors?

Omitting the code will break MPcore processors.

> Are you referring to unified kernels which support both UP and SMP machines?

Of course.

> I reckon that's a recent feature to be able to boot SMP kernels on UP
> machines.

Makes no difference if it's a recent feature or not.  We're not adding
new obstacles to this when we're getting rid of them.  It's counter
productive.

> Perhaps if that's why you're against this, then we need to have a
> separate config option to specifically enable this ARM1136 erratum
> workaround?

No we don't.  Omitting the code is an optimization to what is already a
slow path which results in breakage for people.  That's why I nak'd it.