On Dec 8, 2008, at 9:34 PM, Trent Piepho wrote:
The code that maps kernel low memory would only use page sizes up to
256
MB. On E500v2 pages up to 4 GB are supported.
However, a page must be aligned to a multiple of the page's size.
I.e.
256 MB pages must aligned to a 256 MB boundary. This was enforced
by a
requirement that the physical and virtual addresses of the start of
lowmem
be aligned to 256 MB. Clearly requiring 1GB or 4GB alignment to allow
pages of that size isn't acceptable.
To solve this, I simply have adjust_total_lowmem() take alignment into
account when it decides what size pages to use. Give it PAGE_OFFSET =
0x7000_0000, PHYSICAL_START = 0x3000_0000, and 2GB of RAM, and it
will map
pages like this:
PA 0x3000_0000 VA 0x7000_0000 Size 256 MB
PA 0x4000_0000 VA 0x8000_0000 Size 1 GB
PA 0x8000_0000 VA 0xC000_0000 Size 256 MB
PA 0x9000_0000 VA 0xD000_0000 Size 256 MB
PA 0xA000_0000 VA 0xE000_0000 Size 256 MB
Because the lowmem mapping code now takes alignment into account,
PHYSICAL_ALIGN can be lowered from 256 MB to 64 MB. Even lower
might be
possible. The lowmem code will work down to 4 kB but it's possible
some of
the boot code will fail before then. Poor alignment will force
small pages
to be used, which combined with the limited number of TLB1 pages
available,
will result in very little memory getting mapped. So alignments
less than
64 MB probably aren't very useful anyway.
Signed-off-by: Trent Piepho <tpie...@freescale.com>
---
arch/powerpc/Kconfig | 2 +-
arch/powerpc/mm/fsl_booke_mmu.c | 14 +++++++++++++-
2 files changed, 14 insertions(+), 2 deletions(-)
applied
- k
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