[U-Boot] [PATCH 3/3] ARM: tegra: support large RAM sizes

[Simon Glass]

Hi Stephen,

On 23 December 2014 at 10:34, Stephen Warren <swarren at wwwdotorg.org> wrote:
> From: Stephen Warren <swarren at 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 want 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, we can't use get_ram_size() to verify the actual amount of RAM
> present on such systems, since some of the RAM can't be accesses, which

accessed

> confuses that function. Avoid calling get_ram_size() when the RAM size
> is too large for it to work correctly. It's never actually needed anyway,
> since there's no reason for the BCT to report the wrong RAM size.
>
> In systems with >=4GB RAM, we still need to clip the reported RAM size
> since U-Boot uses a 32-bit variable to represent the RAM size in bytes.
>
> Signed-off-by: Stephen Warren <swarren at nvidia.com>

Reviewed-by: Simon Glass <sjg at chromium.org>

> ---
>  arch/arm/cpu/tegra-common/board.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/cpu/tegra-common/board.c b/arch/arm/cpu/tegra-common/board.c
> index f16fe68a6649..87511a31df18 100644
> --- a/arch/arm/cpu/tegra-common/board.c
> +++ b/arch/arm/cpu/tegra-common/board.c
> @@ -40,7 +40,27 @@ unsigned int query_sdram_size(void)
>         size_bytes = get_ram_size((void *)PHYS_SDRAM_1, emem_cfg * 1024);
>  #else
>         debug("mc->mc_emem_cfg (MEM_SIZE_MB) = 0x%08x\n", emem_cfg);
> -       size_bytes = get_ram_size((void *)PHYS_SDRAM_1, emem_cfg * 1024 * 1024);
> +       /*
> +        * If >=4GB RAM is present, the byte RAM size won't fit into 32-bits
> +        * and will wrap. Clip the reported size to the maximum that a 32-bit
> +        * variable can represent (rounded to a page).
> +        */
> +       if (emem_cfg >= 4096) {
> +               size_bytes = U32_MAX & ~(0x1000 - 1);

Will this return 4GB - 4KB? Why not return the full size?

> +       } else {
> +               /* RAM size EMC is programmed to. */
> +               size_bytes = emem_cfg * 1024 * 1024;
> +               /*
> +                * If all RAM fits within 32-bits, it can be accessed without
> +                * LPAE, so go test the RAM size. Otherwise, we can't access
> +                * all the RAM, and get_ram_size() would get confused, so
> +                * avoid using it. There's no reason we should need this
> +                * validation step anyway.
> +                */
> +               if (emem_cfg <= (0 - PHYS_SDRAM_1) / (1024 * 1024))
> +                       size_bytes = get_ram_size((void *)PHYS_SDRAM_1,
> +                                                 size_bytes);
> +       }
>  #endif
>
>  #if defined(CONFIG_TEGRA30) || defined(CONFIG_TEGRA114)
> --
> 1.9.1
>

Regards,
Simon