[U-Boot] [PATCH v4 3/6] arm: uniphier: add UniPhier SoC support code

[Masahiro YAMADA]

Hi Simon,



2014-09-06 3:59 GMT+09:00 Simon Glass <sjg at chromium.org>:
> Hi Masahiro,
>
> On 4 September 2014 23:50, Masahiro Yamada <yamada.m at jp.panasonic.com> wrote:
>> init_page_table
>
> Why do you need a full page table in this code? Can you not use the
> existing page table features in U-Boot?


I assume you mentioned  mmu_setup() function in arch/arm/lib/cache-cp15.c.
I do know it and actually my boards are using it too.

The hardware specification of UniPhier platform is a little special
and unfortunate in terms of RAM / Cache handling.
UniPhier SoCs have no on-chip SRAM!

Let's assume U-boot is booting from NOR Flash.

We have to setup the stack before junping to board_f(),
but there is no writable memory at this moment on our SoCs.
(UniPhier has SDRAMs, of course, but it is intialized
in board_f().)

To solve the problem, our SoCs use a trick to have stack on L2Cache.
To use cache, MMU must be turned on. (This is ARM specification)

That's why hard-coded, full page table must be placed in the code.

When SDRAM is available, the page table is switched to the one
created in arch/arm/lib/cached-cp15.c,  but which is much lator
(board_r() func.)


Best Regards
Masahiro Yamada