1 files changed, 235 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpu/intel_epb.c b/arch/x86/kernel/cpu/intel_epb.c
new file mode 100644
index 000000000..fbaf12e43
--- /dev/null
+++ b/arch/x86/kernel/cpu/intel_epb.c
@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Intel Performance and Energy Bias Hint support.
+ *
+ * Copyright (C) 2019 Intel Corporation
+ *
+ * Author:
+ *	Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+ */
+
+#include <linux/cpuhotplug.h>
+#include <linux/cpu.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/syscore_ops.h>
+#include <linux/pm.h>
+
+#include <asm/cpu_device_id.h>
+#include <asm/cpufeature.h>
+#include <asm/msr.h>
+
+/**
+ * DOC: overview
+ *
+ * The Performance and Energy Bias Hint (EPB) allows software to specify its
+ * preference with respect to the power-performance tradeoffs present in the
+ * processor.  Generally, the EPB is expected to be set by user space (directly
+ * via sysfs or with the help of the x86_energy_perf_policy tool), but there are
+ * two reasons for the kernel to update it.
+ *
+ * First, there are systems where the platform firmware resets the EPB during
+ * system-wide transitions from sleep states back into the working state
+ * effectively causing the previous EPB updates by user space to be lost.
+ * Thus the kernel needs to save the current EPB values for all CPUs during
+ * system-wide transitions to sleep states and restore them on the way back to
+ * the working state.  That can be achieved by saving EPB for secondary CPUs
+ * when they are taken offline during transitions into system sleep states and
+ * for the boot CPU in a syscore suspend operation, so that it can be restored
+ * for the boot CPU in a syscore resume operation and for the other CPUs when
+ * they are brought back online.  However, CPUs that are already offline when
+ * a system-wide PM transition is started are not taken offline again, but their
+ * EPB values may still be reset by the platform firmware during the transition,
+ * so in fact it is necessary to save the EPB of any CPU taken offline and to
+ * restore it when the given CPU goes back online at all times.
+ *
+ * Second, on many systems the initial EPB value coming from the platform
+ * firmware is 0 ('performance') and at least on some of them that is because
+ * the platform firmware does not initialize EPB at all with the assumption that
+ * the OS will do that anyway.  That sometimes is problematic, as it may cause
+ * the system battery to drain too fast, for example, so it is better to adjust
+ * it on CPU bring-up and if the initial EPB value for a given CPU is 0, the
+ * kernel changes it to 6 ('normal').
+ */
+
+static DEFINE_PER_CPU(u8, saved_epb);
+
+#define EPB_MASK	0x0fULL
+#define EPB_SAVED	0x10ULL
+#define MAX_EPB		EPB_MASK
+
+enum energy_perf_value_index {
+	EPB_INDEX_PERFORMANCE,
+	EPB_INDEX_BALANCE_PERFORMANCE,
+	EPB_INDEX_NORMAL,
+	EPB_INDEX_BALANCE_POWERSAVE,
+	EPB_INDEX_POWERSAVE,
+};
+
+static u8 energ_perf_values[] = {
+	[EPB_INDEX_PERFORMANCE] = ENERGY_PERF_BIAS_PERFORMANCE,
+	[EPB_INDEX_BALANCE_PERFORMANCE] = ENERGY_PERF_BIAS_BALANCE_PERFORMANCE,
+	[EPB_INDEX_NORMAL] = ENERGY_PERF_BIAS_NORMAL,
+	[EPB_INDEX_BALANCE_POWERSAVE] = ENERGY_PERF_BIAS_BALANCE_POWERSAVE,
+	[EPB_INDEX_POWERSAVE] = ENERGY_PERF_BIAS_POWERSAVE,
+};
+
+static int intel_epb_save(void)
+{
+	u64 epb;
+
+	rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
+	/*
+	 * Ensure that saved_epb will always be nonzero after this write even if
+	 * the EPB value read from the MSR is 0.
+	 */
+	this_cpu_write(saved_epb, (epb & EPB_MASK) | EPB_SAVED);
+
+	return 0;
+}
+
+static void intel_epb_restore(void)
+{
+	u64 val = this_cpu_read(saved_epb);
+	u64 epb;
+
+	rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
+	if (val) {
+		val &= EPB_MASK;
+	} else {
+		/*
+		 * Because intel_epb_save() has not run for the current CPU yet,
+		 * it is going online for the first time, so if its EPB value is
+		 * 0 ('performance') at this point, assume that it has not been
+		 * initialized by the platform firmware and set it to 6
+		 * ('normal').
+		 */
+		val = epb & EPB_MASK;
+		if (val == ENERGY_PERF_BIAS_PERFORMANCE) {
+			val = energ_perf_values[EPB_INDEX_NORMAL];
+			pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 'performance'\n");
+		}
+	}
+	wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, (epb & ~EPB_MASK) | val);
+}
+
+static struct syscore_ops intel_epb_syscore_ops = {
+	.suspend = intel_epb_save,
+	.resume = intel_epb_restore,
+};
+
+static const char * const energy_perf_strings[] = {
+	[EPB_INDEX_PERFORMANCE] = "performance",
+	[EPB_INDEX_BALANCE_PERFORMANCE] = "balance-performance",
+	[EPB_INDEX_NORMAL] = "normal",
+	[EPB_INDEX_BALANCE_POWERSAVE] = "balance-power",
+	[EPB_INDEX_POWERSAVE] = "power",
+};
+
+static ssize_t energy_perf_bias_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	unsigned int cpu = dev->id;
+	u64 epb;
+	int ret;
+
+	ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb);
+	if (ret < 0)
+		return ret;
+
+	return sprintf(buf, "%llu\n", epb);
+}
+
+static ssize_t energy_perf_bias_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
+{
+	unsigned int cpu = dev->id;
+	u64 epb, val;
+	int ret;
+
+	ret = __sysfs_match_string(energy_perf_strings,
+				   ARRAY_SIZE(energy_perf_strings), buf);
+	if (ret >= 0)
+		val = energ_perf_values[ret];
+	else if (kstrtou64(buf, 0, &val) || val > MAX_EPB)
+		return -EINVAL;
+
+	ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb);
+	if (ret < 0)
+		return ret;
+
+	ret = wrmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS,
+			    (epb & ~EPB_MASK) | val);
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(energy_perf_bias);
+
+static struct attribute *intel_epb_attrs[] = {
+	&dev_attr_energy_perf_bias.attr,
+	NULL
+};
+
+static const struct attribute_group intel_epb_attr_group = {
+	.name = power_group_name,
+	.attrs =  intel_epb_attrs
+};
+
+static int intel_epb_online(unsigned int cpu)
+{
+	struct device *cpu_dev = get_cpu_device(cpu);
+
+	intel_epb_restore();
+	if (!cpuhp_tasks_frozen)
+		sysfs_merge_group(&cpu_dev->kobj, &intel_epb_attr_group);
+
+	return 0;
+}
+
+static int intel_epb_offline(unsigned int cpu)
+{
+	struct device *cpu_dev = get_cpu_device(cpu);
+
+	if (!cpuhp_tasks_frozen)
+		sysfs_unmerge_group(&cpu_dev->kobj, &intel_epb_attr_group);
+
+	intel_epb_save();
+	return 0;
+}
+
+static const struct x86_cpu_id intel_epb_normal[] = {
+	X86_MATCH_INTEL_FAM6_MODEL(ALDERLAKE_L, 7),
+	{}
+};
+
+static __init int intel_epb_init(void)
+{
+	const struct x86_cpu_id *id = x86_match_cpu(intel_epb_normal);
+	int ret;
+
+	if (!boot_cpu_has(X86_FEATURE_EPB))
+		return -ENODEV;
+
+	if (id)
+		energ_perf_values[EPB_INDEX_NORMAL] = id->driver_data;
+
+	ret = cpuhp_setup_state(CPUHP_AP_X86_INTEL_EPB_ONLINE,
+				"x86/intel/epb:online", intel_epb_online,
+				intel_epb_offline);
+	if (ret < 0)
+		goto err_out_online;
+
+	register_syscore_ops(&intel_epb_syscore_ops);
+	return 0;
+
+err_out_online:
+	cpuhp_remove_state(CPUHP_AP_X86_INTEL_EPB_ONLINE);
+	return ret;
+}
+subsys_initcall(intel_epb_init);