[PATCH v4] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Quentin Schulz]

Hi Alex,

On 10/15/24 12:15 AM, Alex Shumsky wrote:
> Increase rng-seed size to make Linux happy and initialize rng pool instantly.
> Linux 5.19+ requires 32 bytes of entropy to initialize random pool, but u-boot
> currently provides only 8 bytes.
> Linux 5.18 and probably some versions before it used to require 64 bytes.
> Bump min value to 64 bytes to be on a safe side.
> 
> Boot with 8 byte rng-seed (Linux 6.11):
>      # dmesg | grep crng
>      [   12.089286] random: crng init done
> Boot with 32 byte rng-seed (Linux 6.11):
>      # dmesg | grep crng
>      [    0.000000] random: crng init done
> 
> Linux source references:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.19#n551
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.18#n236
> 
> Signed-off-by: Alex Shumsky <alexthreed at gmail.com>
> Fixes: d2048bafae40 ("rockchip: board: Add board_rng_seed() for all Rockchip devices")
> Reviewed-by: Dragan Simic <dsimic at manjaro.org>
> ---
> 
> Changes in v4:
> - fix typos and code style
> 
> Changes in v3:
> - reword warning
> - increase default rng_seed_size to support older linux as well
> - reword commit message
> 
> Changes in v2:
> - add env config knob rng_seed_size
> - add warning for small rng_seed_size
> - 12-character commit SHA in Fixes
> 
>   arch/arm/mach-rockchip/board.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-rockchip/board.c b/arch/arm/mach-rockchip/board.c
> index 3fadf7e412..ca6404776f 100644
> --- a/arch/arm/mach-rockchip/board.c
> +++ b/arch/arm/mach-rockchip/board.c
> @@ -472,9 +472,18 @@ __weak int misc_init_r(void)
>   __weak int board_rng_seed(struct abuf *buf)
>   {
>   	struct udevice *dev;
> -	size_t len = 0x8;
> +	ulong len = env_get_ulong("rng_seed_size", 10, 64);

I'm wondering if we have somewhere some documentation on the environment 
variables that exist and what they used for because this would be a nice 
addition. At the very least, we can mention this variable in:
- include/fdt_support.h for the function
- common/Kconfig for the symbol

I'm also a bit torn on the base though, I think the assumed base is 
generally hex and not dec, so maybe we should rather have that?

Looking good otherwise :)

Cheers,
Quentin