On Sat, Apr 30, 2022 at 02:24:33PM +0200, Jason A. Donenfeld wrote:
> In order to measure the boot process, the timer should be switched on as
> early in boot as possible. This is necessary so that by the time the
> setup code reaches random_init(), get_cycles() (by way of
> random_get_entropy()) returns non-zero, indicating that it is actually
> capable of counting. So this commit enables the timer immediately upon
> booting up. As well, the commit define the get_cycles macro, like the
> previous patches in this series, so that generic code is aware that it's
> implemented by the platform, as is done on other archs.
>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: Jonas Bonn <[email protected]>
> Cc: Stefan Kristiansson <[email protected]>
> Cc: Stafford Horne <[email protected]>
> Signed-off-by: Jason A. Donenfeld <[email protected]>
> ---
> Changes v7->v8:
> - Rather than doing get_cycles()+1 to handle the early boot case,
> actually start the timer early in boot. This has the huge advantage of
> properly measuring the boot sequence timing, which could be a valuable
> source of entropy.
>
> arch/openrisc/include/asm/timex.h | 1 +
> arch/openrisc/kernel/setup.c | 7 +++++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/arch/openrisc/include/asm/timex.h b/arch/openrisc/include/asm/timex.h
> index d52b4e536e3f..5487fa93dd9b 100644
> --- a/arch/openrisc/include/asm/timex.h
> +++ b/arch/openrisc/include/asm/timex.h
> @@ -23,6 +23,7 @@ static inline cycles_t get_cycles(void)
> {
> return mfspr(SPR_TTCR);
> }
> +#define get_cycles get_cycles
>
> /* This isn't really used any more */
> #define CLOCK_TICK_RATE 1000
> diff --git a/arch/openrisc/kernel/setup.c b/arch/openrisc/kernel/setup.c
> index 0cd04d936a7a..1cb7c1770a17 100644
> --- a/arch/openrisc/kernel/setup.c
> +++ b/arch/openrisc/kernel/setup.c
> @@ -220,6 +220,13 @@ void __init setup_cpuinfo(void)
>
> void __init or1k_early_setup(void *fdt)
> {
> + /* Start the TTCR as early as possible, so that the RNG can make use of
> + * measurements of boot time from the earliest opportunity. Especially
> + * important is that the TTCR does not return zero by the time we reach
> + * rand_initialize().
> + */
> + mtspr(SPR_TTMR, SPR_TTMR_CR);
> +
> if (fdt)
> pr_info("FDT at %p\n", fdt);
> else {
It looks like we cross paths on this one.
I can't think of anything better. Also, I tested this on SMP systems and it
works fine.
Acked-by: Stafford Horne <[email protected]>