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 <tglx@xxxxxxxxxxxxx> > Cc: Arnd Bergmann <arnd@xxxxxxxx> > Cc: Jonas Bonn <jonas@xxxxxxxxxxxx> > Cc: Stefan Kristiansson <stefan.kristiansson@xxxxxxxxxxxxx> > Cc: Stafford Horne <shorne@xxxxxxxxx> > Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> > --- > 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 <shorne@xxxxxxxxx>