Messages in this thread | | | Date | Tue, 20 Nov 2018 14:53:16 +0000 | From | Andrew Murray <> | Subject | Re: [PATCH v1 1/1] arm64: Early boot time stamps |
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On Tue, Nov 20, 2018 at 09:40:10AM -0500, Pavel Tatashin wrote: > > > +static __init void sched_clock_early_init(void) > > > +{ > > > + u64 freq = arch_timer_get_cntfrq(); > > > + u64 (*read_time)(void) = arch_counter_get_cntvct; > > > > We already have arch_timer_read_counter which is exposed from > > arm_arch_timer.h. > > OK > > > > > > + > > > + /* Early clock is available only on platforms with known freqs */ > > > > This comment is misleading. It should read something like: > > > > /* > > * The arm64 boot protocol mandates that CNTFRQ_EL0 reflects > > * the timer frequency. To avoid breakage on misconfigured > > * systems, do not register the early sched_clock if the > > * programmed value if zero. Other random values will just > > * result in random output. > > */ > > > > OK > > > > + if (!freq) > > > + return; > > > + > > > + sched_clock_register(read_time, BITS_PER_LONG, freq); > > > > This doesn't seem right. The counter has an architected minimum of 56 > > bits, and you can't assume that it is going to be more than that. > > Yeah, I saw 56 is used in arm_arch_timer.c, but I could not find where > this minimum is defined in aarch64 specs. I will change it to 56.
See section G5.1.2 of the ARM ARM for details.
Thanks,
Andrew Murray
> > I will send v2 soon. > > Thank you, > Pasha
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