On Sun, May 1, 2022 at 12:36 AM Stafford Horne <shorne@xxxxxxxxx> wrote: > > 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> Oh okay. Do you want me to go with this or with the assembly one? Jason