[PATCH] powerpc 8xx: Fixing memory init issue with CONFIG_PIN_TLB

[Scott Wood]

On Tue, 2013-10-15 at 18:27 +0200, leroy christophe wrote:
> Le 11/10/2013 17:13, Joakim Tjernlund a écrit :
> > "Linuxppc-dev"
> > <linuxppc-dev-bounces+joakim.tjernlund=transmode.se at lists.ozlabs.org>
> > wrote on 2013/10/11 14:56:40:
> >> Activating CONFIG_PIN_TLB allows access to the 24 first Mbytes of memory
> > at
> >> bootup instead of 8. It is needed for "big" kernels for instance when
> > activating
> >> CONFIG_LOCKDEP_SUPPORT. This needs to be taken into account in init_32
> > too,
> >> otherwise memory allocation soon fails after startup.
> >>
> >> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
> >>
> >> diff -ur linux-3.11.org/arch/powerpc/kernel/head_8xx.S
> > linux-3.11/arch/powerpc/kernel/head_8xx.S
> >> --- linux-3.11.org/arch/powerpc/mm/init_32.c   2013-09-02
> > 22:46:10.000000000 +0200
> >> +++ linux-3.11/arch/powerpc/mm/init_32.c   2013-09-09 11:28:54.000000000
> > +0200
> >> @@ -213,7 +213,12 @@
> >>       */
> >>      BUG_ON(first_memblock_base != 0);
> >>
> >> +#ifdef CONFIG_PIN_TLB
> >> +   /* 8xx can only access 24MB at the moment */
> >> +   memblock_set_current_limit(min_t(u64, first_memblock_size,
> > 0x01800000));
> >> +#else
> >>      /* 8xx can only access 8MB at the moment */
> >>      memblock_set_current_limit(min_t(u64, first_memblock_size,
> > 0x00800000));
> >> +#endif
> >>   }
> >>   #endif /* CONFIG_8xx */
> > hmm, I think you should always map 24 MB (or less if RAM < 24 MB) and do
> > the same
> > in head_8xx.S.
> >
> > Or to keep it simple, just always map at least 16 MB here and in
> > head_8xx.S, assuming
> > that 16 MB is min RAM for any 8xx system running 3.x kernels.
> Yes we could do a more elaborated modification in the future. However it 
> also has an impact on the boot loader, so I'm not sure we should make it 
> the default without thinking twice.
> 
> In the meantime, my patch does take into account the existing situation 
> where you have 8Mb by default and 24Mb when you activate CONFIG_PIN_TLB.
> I see it as a bug fix and I believe we should include it at least in 
> order to allow including in the stable releases.
> 
> Do you see any issue with this approach ?

The patch is fine, but I don't think it's stable material (BTW, if it
were, you should have marked it as such when submitting).  If I
understand the situation correctly, there's no regression, and nothing
fails to work with CONFIG_PIN_TLB that would have worked without it.
It's just making CONFIG_PIN_TLB more useful.

-Scott