--- zzzz-none-000/linux-4.9.279/arch/x86/kernel/hpet.c	2021-08-08 06:38:54.000000000 +0000
+++ puma7-atom-6591-750/linux-4.9.279/arch/x86/kernel/hpet.c	2023-02-08 11:43:42.000000000 +0000
@@ -12,6 +12,8 @@
 #include <linux/cpu.h>
 #include <linux/pm.h>
 #include <linux/io.h>
+#include <linux/acpi.h>
+#include <acpi/acpi_bus.h>
 
 #include <asm/cpufeature.h>
 #include <asm/irqdomain.h>
@@ -182,6 +184,151 @@
 
 static void hpet_reserve_msi_timers(struct hpet_data *hd);
 
+#if IS_ENABLED(CONFIG_HPET_NMI_TIMER)
+#include <linux/jiffies.h>
+
+static void hpet_stop_counter(void);
+static void hpet_reset_counter(void);
+static void hpet_start_counter(void);
+
+#define AVM_TIMER_NR    2
+static int avm_timer_irq = -ENODEV;
+
+static unsigned int avm_ticks;
+
+static irqreturn_t dummy_interrupt_handler(int irq, void *data)
+{
+	return IRQ_HANDLED;
+}
+
+static int avm_nmi_timer_request_irq(int timer)
+{
+	unsigned long int_route_cap;
+	int irq, ret;
+
+	int_route_cap = hpet_readl(HPET_Tn_CFG(timer)+4);
+
+	/* Try legacy interrupts only, since we are edge-triggered */
+	int_route_cap &= 0xffff;
+
+	ret = -ENODEV;
+	for_each_set_bit(irq, &int_route_cap, HPET_MAX_IRQ) {
+		ret = request_irq(irq, dummy_interrupt_handler,
+				IRQF_TIMER | IRQF_NOBALANCING,
+				"HPET NMI dummy", NULL);
+		if (ret == 0)
+			return irq;
+	}
+
+	return ret;
+}
+
+static void avm_nmi_timer_init(void)
+{
+	unsigned int cfg;
+	int irq;
+
+	irq = avm_nmi_timer_request_irq(AVM_TIMER_NR);
+	if (irq < 0) {
+		pr_err("hpet: Failed to register irq for avm watchdog: %d\n", irq);
+		return;
+	}
+
+	/*
+	 * Program the timer from scratch so that we're independent of
+	 * changes in mainline code.
+	 */
+	cfg = hpet_readl(HPET_Tn_CFG(AVM_TIMER_NR));
+	cfg &= ~(HPET_TN_ENABLE | HPET_TN_LEVEL | HPET_TN_FSB
+			| (HPET_TN_ROUTE << HPET_TN_ROUTE_SHIFT));
+	cfg |= HPET_TN_32BIT | (irq << HPET_TN_ROUTE_SHIFT);
+	hpet_writel(cfg, HPET_Tn_CFG(AVM_TIMER_NR));
+
+	pr_info("Using HPET timer %d for AVM NMI watchdog, irq %d.\n",
+			AVM_TIMER_NR, irq);
+
+	hpet_print_config();
+	avm_timer_irq = irq;
+}
+
+void avm_nmi_timer_update(void)
+{
+	unsigned int cmp, now;
+
+	now = hpet_readl(HPET_COUNTER);
+	cmp = now + avm_ticks;
+
+	hpet_writel(cmp, HPET_Tn_CMP(AVM_TIMER_NR));
+}
+EXPORT_SYMBOL(avm_nmi_timer_update);
+
+int avm_nmi_timer_start(int seconds, const cpumask_t *mask)
+{
+	unsigned long long ticks_per_sec;
+	unsigned int cfg, period;
+	int result;
+
+	result = 0;
+	if (seconds <= 0) {
+		result = -EINVAL;
+		goto err_out;
+	}
+
+	if (avm_timer_irq < 0)
+		return -ENODEV;
+
+	result = IO_APIC_enable_nmi(avm_timer_irq, mask);
+	if (result != 0) {
+		pr_err("[%s] Enabling NMI failed.\n", __func__);
+		goto err_out;
+	}
+
+	period = hpet_readl(HPET_PERIOD);
+	ticks_per_sec = DIV_ROUND_CLOSEST_ULL(FSEC_PER_SEC, period);
+	avm_ticks = seconds * ticks_per_sec;
+
+	pr_info("[%s] Starting AVM NMI timer on cpus #%*pbl. Period %d seconds, %d ticks\n",
+		__func__, cpumask_pr_args(mask), seconds, avm_ticks);
+
+	avm_nmi_timer_update();
+	cfg = hpet_readl(HPET_Tn_CFG(AVM_TIMER_NR));
+	cfg |= HPET_TN_ENABLE;
+
+	hpet_writel(cfg, HPET_Tn_CFG(AVM_TIMER_NR));
+	hpet_start_counter();
+
+err_out:
+	return result;
+}
+EXPORT_SYMBOL(avm_nmi_timer_start);
+
+void avm_nmi_timer_stop(void)
+{
+	unsigned int cfg;
+
+	cfg = hpet_readl(HPET_Tn_CFG(AVM_TIMER_NR));
+	cfg &= ~(HPET_TN_ENABLE);
+
+	hpet_writel(cfg, HPET_Tn_CFG(AVM_TIMER_NR));
+	if (avm_timer_irq >= 0) {
+		IO_APIC_disable_nmi(avm_timer_irq);
+		avm_timer_irq = -ENODEV;
+	}
+}
+EXPORT_SYMBOL(avm_nmi_timer_stop);
+
+bool avm_nmi_timer_expired(void)
+{
+	unsigned long cmp, now;
+
+	now = hpet_readl(HPET_COUNTER);
+	cmp = hpet_readl(HPET_Tn_CMP(AVM_TIMER_NR));
+
+	return time_after_eq(now, cmp);
+}
+EXPORT_SYMBOL(avm_nmi_timer_expired);
+#endif /* IS_ENABLED(CONFIG_HPET_NMI_TIMER) */
+
 static void hpet_reserve_platform_timers(unsigned int id)
 {
 	struct hpet __iomem *hpet = hpet_virt_address;
@@ -201,6 +348,10 @@
 	hpet_reserve_timer(&hd, 1);
 #endif
 
+#if IS_ENABLED(CONFIG_HPET_NMI_TIMER)
+	hpet_reserve_timer(&hd, AVM_TIMER_NR);
+#endif
+
 	/*
 	 * NOTE that hd_irq[] reflects IOAPIC input pins (LEGACY_8254
 	 * is wrong for i8259!) not the output IRQ.  Many BIOS writers
@@ -999,6 +1150,11 @@
 			pr_warn("HPET: Unrecognized bits %#x set in cfg#%u\n",
 				cfg, i);
 	}
+
+#if defined(CONFIG_HPET_NMI_TIMER)
+	avm_nmi_timer_init();
+#endif
+
 	hpet_print_config();
 
 	if (hpet_clocksource_register())