Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
timekeeping: Provide interface to control auxiliary clocks
Auxiliary clocks are disabled by default and attempts to access them
fail.
Provide an interface to enable/disable them at run-time.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250625183758.444626478@linutronix.de
+121
+5
Documentation/ABI/stable/sysfs-kernel-time-aux-clocks
+5
Documentation/ABI/stable/sysfs-kernel-time-aux-clocks
+116
kernel/time/timekeeping.c
+116
kernel/time/timekeeping.c
···
6
6
#include <linux/timekeeper_internal.h>
7
7
#include <linux/module.h>
8
8
#include <linux/interrupt.h>
9
+
#include <linux/kobject.h>
9
10
#include <linux/percpu.h>
10
11
#include <linux/init.h>
11
12
#include <linux/mm.h>
···
2916
2915
.clock_set = aux_clock_set,
2917
2916
.clock_adj = aux_clock_adj,
2918
2917
};
2918
+
2919
+
static void aux_clock_enable(clockid_t id)
2920
+
{
2921
+
struct tk_read_base *tkr_raw = &tk_core.timekeeper.tkr_raw;
2922
+
struct tk_data *aux_tkd = aux_get_tk_data(id);
2923
+
struct timekeeper *aux_tks = &aux_tkd->shadow_timekeeper;
2924
+
2925
+
/* Prevent the core timekeeper from changing. */
2926
+
guard(raw_spinlock_irq)(&tk_core.lock);
2927
+
2928
+
/*
2929
+
* Setup the auxiliary clock assuming that the raw core timekeeper
2930
+
* clock frequency conversion is close enough. Userspace has to
2931
+
* adjust for the deviation via clock_adjtime(2).
2932
+
*/
2933
+
guard(raw_spinlock_nested)(&aux_tkd->lock);
2934
+
2935
+
/* Remove leftovers of a previous registration */
2936
+
memset(aux_tks, 0, sizeof(*aux_tks));
2937
+
/* Restore the timekeeper id */
2938
+
aux_tks->id = aux_tkd->timekeeper.id;
2939
+
/* Setup the timekeeper based on the current system clocksource */
2940
+
tk_setup_internals(aux_tks, tkr_raw->clock);
2941
+
2942
+
/* Mark it valid and set it live */
2943
+
aux_tks->clock_valid = true;
2944
+
timekeeping_update_from_shadow(aux_tkd, TK_UPDATE_ALL);
2945
+
}
2946
+
2947
+
static void aux_clock_disable(clockid_t id)
2948
+
{
2949
+
struct tk_data *aux_tkd = aux_get_tk_data(id);
2950
+
2951
+
guard(raw_spinlock_irq)(&aux_tkd->lock);
2952
+
aux_tkd->shadow_timekeeper.clock_valid = false;
2953
+
timekeeping_update_from_shadow(aux_tkd, TK_UPDATE_ALL);
2954
+
}
2955
+
2956
+
static DEFINE_MUTEX(aux_clock_mutex);
2957
+
2958
+
static ssize_t aux_clock_enable_store(struct kobject *kobj, struct kobj_attribute *attr,
2959
+
const char *buf, size_t count)
2960
+
{
2961
+
/* Lazy atoi() as name is "0..7" */
2962
+
int id = kobj->name[0] & 0x7;
2963
+
bool enable;
2964
+
2965
+
if (!capable(CAP_SYS_TIME))
2966
+
return -EPERM;
2967
+
2968
+
if (kstrtobool(buf, &enable) < 0)
2969
+
return -EINVAL;
2970
+
2971
+
guard(mutex)(&aux_clock_mutex);
2972
+
if (enable == test_bit(id, &aux_timekeepers))
2973
+
return count;
2974
+
2975
+
if (enable) {
2976
+
aux_clock_enable(CLOCK_AUX + id);
2977
+
set_bit(id, &aux_timekeepers);
2978
+
} else {
2979
+
aux_clock_disable(CLOCK_AUX + id);
2980
+
clear_bit(id, &aux_timekeepers);
2981
+
}
2982
+
return count;
2983
+
}
2984
+
2985
+
static ssize_t aux_clock_enable_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
2986
+
{
2987
+
unsigned long active = READ_ONCE(aux_timekeepers);
2988
+
/* Lazy atoi() as name is "0..7" */
2989
+
int id = kobj->name[0] & 0x7;
2990
+
2991
+
return sysfs_emit(buf, "%d\n", test_bit(id, &active));
2992
+
}
2993
+
2994
+
static struct kobj_attribute aux_clock_enable_attr = __ATTR_RW(aux_clock_enable);
2995
+
2996
+
static struct attribute *aux_clock_enable_attrs[] = {
2997
+
&aux_clock_enable_attr.attr,
2998
+
NULL
2999
+
};
3000
+
3001
+
static const struct attribute_group aux_clock_enable_attr_group = {
3002
+
.attrs = aux_clock_enable_attrs,
3003
+
};
3004
+
3005
+
static int __init tk_aux_sysfs_init(void)
3006
+
{
3007
+
struct kobject *auxo, *tko = kobject_create_and_add("time", kernel_kobj);
3008
+
3009
+
if (!tko)
3010
+
return -ENOMEM;
3011
+
3012
+
auxo = kobject_create_and_add("aux_clocks", tko);
3013
+
if (!auxo) {
3014
+
kobject_put(tko);
3015
+
return -ENOMEM;
3016
+
}
3017
+
3018
+
for (int i = 0; i <= MAX_AUX_CLOCKS; i++) {
3019
+
char id[2] = { [0] = '0' + i, };
3020
+
struct kobject *clk = kobject_create_and_add(id, auxo);
3021
+
3022
+
if (!clk)
3023
+
return -ENOMEM;
3024
+
3025
+
int ret = sysfs_create_group(clk, &aux_clock_enable_attr_group);
3026
+
3027
+
if (ret)
3028
+
return ret;
3029
+
}
3030
+
return 0;
3031
+
}
3032
+
late_initcall(tk_aux_sysfs_init);
2919
3033
2920
3034
static __init void tk_aux_setup(void)
2921
3035
{