Hi Stephen,
On 23 December 2014 at 10:34, Stephen Warren <swar...@wwwdotorg.org> wrote:
> From: Stephen Warren <swar...@nvidia.com>
>
> Some systems have so much RAM that the end of RAM is beyond 4GB. An
> example would be a Tegra124 system (where RAM starts at 2GB physical)
> that has more than 2GB of RAM.
>
> In this case, we can gd->ram_size to represent the actual RAM size, so
> that the actual RAM size is passed to the OS. This is useful if the OS
> implements LPAE, and can actually use the "extra" RAM.
>
> However, U-Boot does not implement LPAE and so must deal with 32-bit
> physical addresses. To this end, we enhance board_get_usable_ram_top() to
> detect the "over-sized" case, and limit the relocation addres so that it
> fits into 32-bits of physical address space.
>
> Signed-off-by: Stephen Warren <swar...@nvidia.com>
Reviewed-by: Simon Glass <s...@chromium.org>
> ---
> common/board_f.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/common/board_f.c b/common/board_f.c
> index 98c9c728ce73..c1ada8d62009 100644
> --- a/common/board_f.c
> +++ b/common/board_f.c
> @@ -360,6 +360,18 @@ static int setup_fdt(void)
> /* Get the top of usable RAM */
> __weak ulong board_get_usable_ram_top(ulong total_size)
> {
> +#ifdef CONFIG_SYS_SDRAM_BASE
> + /*
> + * Detect whether we have so much RAM it goes past the end of our
> + * 32-bit address space. If so, clip the usable RAM so it doesn't.
> + */
> + if (gd->ram_top < CONFIG_SYS_SDRAM_BASE)
> + /*
> + * Will wrap back to top of 32-bit space when reservations
> + * are made.
> + */
> + return 0;
I wonder whether (ulong)(1ULL << 32) would be more portable, but
perhaps it would just be confusing. We can worry about this when we do
more 64-bit things.
> +#endif
> return gd->ram_top;
> }
>
> --
> 1.9.1
>
Regards,
Simon
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