On 18-11-21 17:47:07, Will Deacon wrote:
> > + /*
> > + * 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.
> > + */
> > + if (!freq)
> > + return;
> > +
> > + arch_timer_read_counter = arch_counter_get_cntvct;
>
> Why do you need to assign this here?
>
> > + sched_clock_register(arch_timer_read_counter, ARCH_TIMER_NBITS, freq);
>
> arch_timer_read_counter can be reassigned once the arm_arch_timer driver
> has probed; what stops this from being unused as the sched_clock after that
> has happened? I worry that toggling the function pointer could lead to
> sched_clock() going backwards.
No reason, I will revert it back to use a local variable. I agree, time
can go backward for a period of time while we switch to permanent clock later,
if that clock is different.
>
> > +}
> > +
> > void __init setup_arch(char **cmdline_p)
> > {
> > + sched_clock_early_init();
> > +
> > init_mm.start_code = (unsigned long) _text;
> > init_mm.end_code = (unsigned long) _etext;
> > init_mm.end_data = (unsigned long) _edata;
>
> The patch from this point onwards just looks like a refactoring to me which
> should be independent of adding early printk timestamps. Also, it doesn't
> update the vdso logic, which hardwires a 56-bit mask for the counter values.
OK, I will split the patch, and will also address the hard coded value
here:
https://soleen.com/source/xref/linux/arch/arm64/kernel/vdso/gettimeofday.S?r=c80ed088#73
Are there more that you know of?
Thank you,
Pasha
