[U-Boot] [PATCH 2/5] sunxi: add Kconfig option for the maximum accessible DRAM

[André Przywara]

On 07/02/18 19:35, Icenowy Zheng wrote:
> Allwinner 64-bit SoCs can use 4GiB DRAM chip, however their memory map
> has only allocated 3GiB for DRAM, so only 3GiB of the DRAM is
> accessible.
> 
> Add a Kconfig option for the maximum accessible DRAM.

That looks fine to me, but have you checked CONFIG_MAX_MEM_MAPPED?
get_effective_memsize() in common/memsize.c looks like it's solving this
very problem.

> For A80 it should be a much higher value (8GiB), but as I have no A80
> device to test and originally U-Boot only supports 2GiB DRAM on A80, it
> currently still falls under the 2GiB situation.

Well, that depends on how we will use SUNXI_DRAM_SIZE. If that's to
limit the size we eventually report in the DT, that should be indeed 8GB
on the A80. But U-Boot itself can't use more than 3GB on sunxi/ARMv7
(due to the static 1:1 mapping).
I think we should separate those two numbers (actual DRAM size and
U-Boot's own DRAM size), if we really want to support >3GB on the A80.

But maybe we should not get carried away by something that doesn't
really exist.

Thanks,
Andre.

> 
> Signed-off-by: Icenowy Zheng <icenowy at aosc.io>
> ---
>  arch/arm/mach-sunxi/Kconfig | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
> index 1fededd0a3..32739e0f33 100644
> --- a/arch/arm/mach-sunxi/Kconfig
> +++ b/arch/arm/mach-sunxi/Kconfig
> @@ -63,6 +63,13 @@ config MACH_SUNXI_H3_H5
>  	select SUNXI_GEN_SUN6I
>  	select SUPPORT_SPL
>  
> +# TODO: try out A80's 8GiB DRAM space
> +config SUNXI_DRAM_MAX_SIZE
> +	hex
> +	default 0xC0000000 if MACH_SUN50I
> +	default 0xC0000000 if MACH_SUN50I_H5
> +	default 0x80000000
> +
>  choice
>  	prompt "Sunxi SoC Variant"
>  	optional
>