[U-Boot] Dynamically determine RAM size and pass it to kernel

[Mike Looijmans]

On 17-11-16 13:34, Mike Looijmans wrote:
> We have some Zynq based boards still in the field that have only 512MB RAM
> instead of 1GB. The memory chips are compatible and use the same settings
> apart from that one extra address bit.
>
> So what works is just configure the DDR controller for 1GB and then check if
> writing some data "wraps" back, this is my "spike" code in the RAM init code
> for that:
>
> +       u32 *ptr_1 = (u32*)0x10000;
> +       u32 *ptr_2 = (u32*)((gd->ram_size >> 1) + 0x10000);
> +
> +       puts("RAM test");
> +       *ptr_1 = 0x12345678;
> +       if (*ptr_2 == *ptr_1) {
> +               *ptr_1 = 0x87654321;
> +               if (*ptr_2 == *ptr_1) {
> +                       puts(" [HALF]");
> +                       gd->ram_size >>= 1;
> +               }
> +       }

I found that I can replace that with "get_mem_size()" which does this better.

>
> This works well, and reliably detects that the board only has half the amount
> of RAM, and corrects the ram_size variable.
>
> The problem I'm seeing now is that this new ram_size does not get passed to
> the kernel. Apparently in modern versions of u-boot I need to somehow patch
> the "live" devicetree blob as well? How does that work?





Kind regards,

Mike Looijmans
System Expert

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E-mail: mike.looijmans at topicproducts.com
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