Re: [PATCH 2/2] powerpc/e6500: TLB miss handler with hardware tablewalk support

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

On Fri, 2012-06-15 at 11:50 -0500, Scott Wood wrote:
> On 06/14/2012 08:05 PM, Benjamin Herrenschmidt wrote:
> >>  - It has threads, but no "tlbsrx." -- so we need a spinlock and
> >>    a normal "tlbsx".  Because we need this lock, hardware tablewalk
> >>    is mandatory on e6500 unless we want to add spinlock+tlbsx to
> >>    the normal bolted TLB miss handler.
> > 
> > Isn't this a violation of the architecture ? (Isn't tlbsrx. mandatory ?
> > in 2.06 MAV2 ?).
> 
> I don't think so -- not only does it have a category name, there's a
> MAV2-specific bit in MMUCSR indicating whether the category is present.
> 
> I still don't understand why Freescale omitted it from a chip that has
> threads, though.

Right, especially since from memory, the idea for it came from FSL (Mike
maybe) during a meeting between the IBM and FSL folks (I was there) :-)

Oh well .... probably a case of HW folks with no clue that didn't
understand why it would be needed. Did you whack a few heads with a
cluebat ?

Cheers,
Ben.