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

[Marek Vasut]

On 10/15/24 11:34 AM, Quentin Schulz wrote:
> 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?
It is a decimal number, similar to e.g. bootcount , hence base 10 .