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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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022eb8ae8b
On platforms implementing CPU power management, the CPUidle subsystem can allow CPUs to enter idle states where local timers logic is lost on power down. To keep the software timers functional the kernel relies on an always-on broadcast timer to be present in the platform to relay the interrupt signalling the timer expiries. For platforms implementing CPU core gating that do not implement an always-on HW timer or implement it in a broken way, this patch adds code to initialize the kernel hrtimer based clock event device upon boot (which can be chosen as tick broadcast device by the kernel). It relies on a dynamically chosen CPU to be always powered-up. This CPU then relays the timer interrupt to CPUs in deep-idle states through its HW local timer device. Having a CPU always-on has implications on power management platform capabilities and makes CPUidle suboptimal, since at least a CPU is kept always in a shallow idle state by the kernel to relay timer interrupts, but at least leaves the kernel with a functional system with some working power management capabilities. The hrtimer based clock event device is unconditionally registered, but has the lowest possible rating such that any broadcast-capable HW clock event device present will be chosen in preference as the tick broadcast device. Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
114 lines
2.5 KiB
C
114 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/arch/arm/kernel/time.c
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*
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* Copyright (C) 1991, 1992, 1995 Linus Torvalds
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* Modifications for ARM (C) 1994-2001 Russell King
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*
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* This file contains the ARM-specific time handling details:
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* reading the RTC at bootup, etc...
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*/
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#include <linux/clk-provider.h>
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#include <linux/clockchips.h>
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#include <linux/clocksource.h>
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#include <linux/errno.h>
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#include <linux/export.h>
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#include <linux/init.h>
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#include <linux/interrupt.h>
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#include <linux/irq.h>
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#include <linux/kernel.h>
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#include <linux/profile.h>
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#include <linux/sched.h>
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#include <linux/sched_clock.h>
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#include <linux/smp.h>
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#include <linux/time.h>
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#include <linux/timex.h>
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#include <linux/timer.h>
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#include <asm/mach/arch.h>
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#include <asm/mach/time.h>
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#include <asm/stacktrace.h>
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#include <asm/thread_info.h>
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#if defined(CONFIG_RTC_DRV_CMOS) || defined(CONFIG_RTC_DRV_CMOS_MODULE) || \
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defined(CONFIG_NVRAM) || defined(CONFIG_NVRAM_MODULE)
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/* this needs a better home */
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DEFINE_SPINLOCK(rtc_lock);
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EXPORT_SYMBOL(rtc_lock);
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#endif /* pc-style 'CMOS' RTC support */
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/* change this if you have some constant time drift */
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#define USECS_PER_JIFFY (1000000/HZ)
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#ifdef CONFIG_SMP
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unsigned long profile_pc(struct pt_regs *regs)
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{
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struct stackframe frame;
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if (!in_lock_functions(regs->ARM_pc))
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return regs->ARM_pc;
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arm_get_current_stackframe(regs, &frame);
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do {
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int ret = unwind_frame(&frame);
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if (ret < 0)
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return 0;
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} while (in_lock_functions(frame.pc));
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return frame.pc;
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}
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EXPORT_SYMBOL(profile_pc);
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#endif
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#ifndef CONFIG_GENERIC_CLOCKEVENTS
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/*
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* Kernel system timer support.
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*/
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void timer_tick(void)
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{
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profile_tick(CPU_PROFILING);
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xtime_update(1);
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#ifndef CONFIG_SMP
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update_process_times(user_mode(get_irq_regs()));
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#endif
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}
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#endif
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static void dummy_clock_access(struct timespec64 *ts)
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{
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ts->tv_sec = 0;
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ts->tv_nsec = 0;
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}
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static clock_access_fn __read_persistent_clock = dummy_clock_access;
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void read_persistent_clock64(struct timespec64 *ts)
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{
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__read_persistent_clock(ts);
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}
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int __init register_persistent_clock(clock_access_fn read_persistent)
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{
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/* Only allow the clockaccess functions to be registered once */
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if (__read_persistent_clock == dummy_clock_access) {
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if (read_persistent)
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__read_persistent_clock = read_persistent;
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return 0;
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}
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return -EINVAL;
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}
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void __init time_init(void)
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{
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if (machine_desc->init_time) {
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machine_desc->init_time();
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} else {
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#ifdef CONFIG_COMMON_CLK
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of_clk_init(NULL);
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#endif
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timer_probe();
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tick_setup_hrtimer_broadcast();
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}
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}
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