[PATCH 1/2] powerpc: enable the relocatable support for the fsl booke 32bit kernel

[Kevin Hao]

On Thu, Jun 27, 2013 at 08:52:20PM -0500, Scott Wood wrote:
> On 06/27/2013 08:36:37 PM, Kevin Hao wrote:
> >On Thu, Jun 27, 2013 at 02:58:34PM -0500, Scott Wood wrote:
> >> On 06/26/2013 09:00:33 PM, Kevin Hao wrote:
> >> >This is based on the codes in the head_44x.S. Since we always
> >align to
> >> >256M before mapping the PAGE_OFFSET for a relocatable kernel,
> >we also
> >> >change the init tlb map to 256M size.
> >>
> >> Why 256M?
> >
> >For two reasons:
> >  1. This is the size which both e500v1 and e500v2 support.
> >  2. Since we always use the PAGE_OFFSET as 0xc0000000, the 256M is
> >     max alignment value we can use for this virtual address.
> 
> 0xc0000000 is 1G-aligned, so I don't see why 256M is the maximum
> (after verifying that enough memory is present with the right
> alignment, of course).  The TLB1 savings would probably not be
> enough to justify figuring that out, though.

Sorry, I didn't make myself clear. Yes, the 0xc0000000 is 1G-aligned.
For a 32bit kernel we only have a 1G memory region for the kernel space,
but we can't use all of it for direct map. So we always set the
__max_low_memory to 0x30000000. And for e500 core, it doesn't support
512M page size. So the 256M is the max page size we can use for a
32bit kernel. And since we always cover the boot code in the first
tlb entry, we then use the 256M as the alignment value for the
relocatable kernel.

Thanks,
Kevin

> 
> -Scott
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 490 bytes
Desc: not available
URL: <http://lists.ozlabs.org/pipermail/linuxppc-dev/attachments/20130630/86d26dca/attachment.sig>