Hi Pavel,
On 19/11/2018 21:44, Pavel Tatashin wrote:
> Allow printk time stamps/sched_clock() to be available from the early
> boot.
>
> Signed-off-by: Pavel Tatashin <pasha.tatas...@soleen.com>
> ---
> arch/arm64/kernel/setup.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index f4fc1e0544b7..4df41a66b403 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -40,6 +40,7 @@
> #include <linux/efi.h>
> #include <linux/psci.h>
> #include <linux/sched/task.h>
> +#include <linux/sched_clock.h>
> #include <linux/mm.h>
>
> #include <asm/acpi.h>
> @@ -279,8 +280,26 @@ arch_initcall(reserve_memblock_reserved_regions);
>
> u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };
>
> +/*
> + * Get time stamps available early in boot, useful to identify boot time
> issues
> + * from the early boot.
> + */
> +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.
> +
> + /* 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.
*/
> + 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.
> +}
> +
> 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;
>
Thanks,
M.
--
Jazz is not dead. It just smells funny...
