Re: [PATCH v7 11/17] openrisc: account for 0 starting value in random_get_entropy()

[Stafford Horne]

Hi Jason,

On Fri, Apr 29, 2022 at 02:16:48AM +0200, Jason A. Donenfeld wrote:
> As a sanity check, this series makes sure that during early boot, the
> cycle counter isn't returning all zeros. However, OpenRISC's TTCR timer
> can be rather slow and starts out as zero during stages of early boot.
> We know it works, however. So just always add 1 to random_get_entropy()
> so that it doesn't trigger these checks.

Just one nit, you might want to qualify that this is related to simulators/qemu:
 * "However, in simulators OpenRISC's TTCR timer can be rather slow..."

> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Jonas Bonn <jonas@xxxxxxxxxxxx>
> Cc: Stefan Kristiansson <stefan.kristiansson@xxxxxxxxxxxxx>
> Acked-by: Stafford Horne <shorne@xxxxxxxxx>
> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
> ---
> Changes v6->v7:
> - Add 1 to cycle counter to account for functional but slow-to-begin
>   counter on QEMU.
> 
>  arch/openrisc/include/asm/timex.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/openrisc/include/asm/timex.h b/arch/openrisc/include/asm/timex.h
> index d52b4e536e3f..a78a5807c927 100644
> --- a/arch/openrisc/include/asm/timex.h
> +++ b/arch/openrisc/include/asm/timex.h
> @@ -23,6 +23,9 @@ static inline cycles_t get_cycles(void)
>  {
>  	return mfspr(SPR_TTCR);
>  }
> +#define get_cycles get_cycles
> +
> +#define random_get_entropy() ((unsigned long)get_cycles() + 1)
>  
>  /* This isn't really used any more */
>  #define CLOCK_TICK_RATE 1000

Thanks,

-Stafford