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1 : : // SPDX-License-Identifier: GPL-2.0
2 : : /*
3 : : * Intel Performance and Energy Bias Hint support.
4 : : *
5 : : * Copyright (C) 2019 Intel Corporation
6 : : *
7 : : * Author:
8 : : * Rafael J. Wysocki <rafael.j.wysocki@intel.com>
9 : : */
10 : :
11 : : #include <linux/cpuhotplug.h>
12 : : #include <linux/cpu.h>
13 : : #include <linux/device.h>
14 : : #include <linux/kernel.h>
15 : : #include <linux/string.h>
16 : : #include <linux/syscore_ops.h>
17 : : #include <linux/pm.h>
18 : :
19 : : #include <asm/cpufeature.h>
20 : : #include <asm/msr.h>
21 : :
22 : : /**
23 : : * DOC: overview
24 : : *
25 : : * The Performance and Energy Bias Hint (EPB) allows software to specify its
26 : : * preference with respect to the power-performance tradeoffs present in the
27 : : * processor. Generally, the EPB is expected to be set by user space (directly
28 : : * via sysfs or with the help of the x86_energy_perf_policy tool), but there are
29 : : * two reasons for the kernel to update it.
30 : : *
31 : : * First, there are systems where the platform firmware resets the EPB during
32 : : * system-wide transitions from sleep states back into the working state
33 : : * effectively causing the previous EPB updates by user space to be lost.
34 : : * Thus the kernel needs to save the current EPB values for all CPUs during
35 : : * system-wide transitions to sleep states and restore them on the way back to
36 : : * the working state. That can be achieved by saving EPB for secondary CPUs
37 : : * when they are taken offline during transitions into system sleep states and
38 : : * for the boot CPU in a syscore suspend operation, so that it can be restored
39 : : * for the boot CPU in a syscore resume operation and for the other CPUs when
40 : : * they are brought back online. However, CPUs that are already offline when
41 : : * a system-wide PM transition is started are not taken offline again, but their
42 : : * EPB values may still be reset by the platform firmware during the transition,
43 : : * so in fact it is necessary to save the EPB of any CPU taken offline and to
44 : : * restore it when the given CPU goes back online at all times.
45 : : *
46 : : * Second, on many systems the initial EPB value coming from the platform
47 : : * firmware is 0 ('performance') and at least on some of them that is because
48 : : * the platform firmware does not initialize EPB at all with the assumption that
49 : : * the OS will do that anyway. That sometimes is problematic, as it may cause
50 : : * the system battery to drain too fast, for example, so it is better to adjust
51 : : * it on CPU bring-up and if the initial EPB value for a given CPU is 0, the
52 : : * kernel changes it to 6 ('normal').
53 : : */
54 : :
55 : : static DEFINE_PER_CPU(u8, saved_epb);
56 : :
57 : : #define EPB_MASK 0x0fULL
58 : : #define EPB_SAVED 0x10ULL
59 : : #define MAX_EPB EPB_MASK
60 : :
61 : 0 : static int intel_epb_save(void)
62 : : {
63 : 0 : u64 epb;
64 : :
65 : 0 : rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
66 : : /*
67 : : * Ensure that saved_epb will always be nonzero after this write even if
68 : : * the EPB value read from the MSR is 0.
69 : : */
70 : 0 : this_cpu_write(saved_epb, (epb & EPB_MASK) | EPB_SAVED);
71 : :
72 : 0 : return 0;
73 : : }
74 : :
75 : 0 : static void intel_epb_restore(void)
76 : : {
77 : 0 : u64 val = this_cpu_read(saved_epb);
78 : 0 : u64 epb;
79 : :
80 : 0 : rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
81 [ # # ]: 0 : if (val) {
82 : 0 : val &= EPB_MASK;
83 : : } else {
84 : : /*
85 : : * Because intel_epb_save() has not run for the current CPU yet,
86 : : * it is going online for the first time, so if its EPB value is
87 : : * 0 ('performance') at this point, assume that it has not been
88 : : * initialized by the platform firmware and set it to 6
89 : : * ('normal').
90 : : */
91 : 0 : val = epb & EPB_MASK;
92 [ # # ]: 0 : if (val == ENERGY_PERF_BIAS_PERFORMANCE) {
93 : 0 : val = ENERGY_PERF_BIAS_NORMAL;
94 [ # # ]: 0 : pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 'performance'\n");
95 : : }
96 : : }
97 : 0 : wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, (epb & ~EPB_MASK) | val);
98 : 0 : }
99 : :
100 : : static struct syscore_ops intel_epb_syscore_ops = {
101 : : .suspend = intel_epb_save,
102 : : .resume = intel_epb_restore,
103 : : };
104 : :
105 : : static const char * const energy_perf_strings[] = {
106 : : "performance",
107 : : "balance-performance",
108 : : "normal",
109 : : "balance-power",
110 : : "power"
111 : : };
112 : : static const u8 energ_perf_values[] = {
113 : : ENERGY_PERF_BIAS_PERFORMANCE,
114 : : ENERGY_PERF_BIAS_BALANCE_PERFORMANCE,
115 : : ENERGY_PERF_BIAS_NORMAL,
116 : : ENERGY_PERF_BIAS_BALANCE_POWERSAVE,
117 : : ENERGY_PERF_BIAS_POWERSAVE
118 : : };
119 : :
120 : 0 : static ssize_t energy_perf_bias_show(struct device *dev,
121 : : struct device_attribute *attr,
122 : : char *buf)
123 : : {
124 : 0 : unsigned int cpu = dev->id;
125 : 0 : u64 epb;
126 : 0 : int ret;
127 : :
128 : 0 : ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb);
129 [ # # ]: 0 : if (ret < 0)
130 : 0 : return ret;
131 : :
132 : 0 : return sprintf(buf, "%llu\n", epb);
133 : : }
134 : :
135 : 0 : static ssize_t energy_perf_bias_store(struct device *dev,
136 : : struct device_attribute *attr,
137 : : const char *buf, size_t count)
138 : : {
139 : 0 : unsigned int cpu = dev->id;
140 : 0 : u64 epb, val;
141 : 0 : int ret;
142 : :
143 : 0 : ret = __sysfs_match_string(energy_perf_strings,
144 : : ARRAY_SIZE(energy_perf_strings), buf);
145 [ # # ]: 0 : if (ret >= 0)
146 : 0 : val = energ_perf_values[ret];
147 [ # # # # ]: 0 : else if (kstrtou64(buf, 0, &val) || val > MAX_EPB)
148 : : return -EINVAL;
149 : :
150 : 0 : ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb);
151 [ # # ]: 0 : if (ret < 0)
152 : 0 : return ret;
153 : :
154 : 0 : ret = wrmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS,
155 : 0 : (epb & ~EPB_MASK) | val);
156 [ # # ]: 0 : if (ret < 0)
157 : 0 : return ret;
158 : :
159 : 0 : return count;
160 : : }
161 : :
162 : : static DEVICE_ATTR_RW(energy_perf_bias);
163 : :
164 : : static struct attribute *intel_epb_attrs[] = {
165 : : &dev_attr_energy_perf_bias.attr,
166 : : NULL
167 : : };
168 : :
169 : : static const struct attribute_group intel_epb_attr_group = {
170 : : .name = power_group_name,
171 : : .attrs = intel_epb_attrs
172 : : };
173 : :
174 : 0 : static int intel_epb_online(unsigned int cpu)
175 : : {
176 : 0 : struct device *cpu_dev = get_cpu_device(cpu);
177 : :
178 : 0 : intel_epb_restore();
179 [ # # ]: 0 : if (!cpuhp_tasks_frozen)
180 : 0 : sysfs_merge_group(&cpu_dev->kobj, &intel_epb_attr_group);
181 : :
182 : 0 : return 0;
183 : : }
184 : :
185 : 0 : static int intel_epb_offline(unsigned int cpu)
186 : : {
187 : 0 : struct device *cpu_dev = get_cpu_device(cpu);
188 : :
189 [ # # ]: 0 : if (!cpuhp_tasks_frozen)
190 : 0 : sysfs_unmerge_group(&cpu_dev->kobj, &intel_epb_attr_group);
191 : :
192 : 0 : intel_epb_save();
193 : 0 : return 0;
194 : : }
195 : :
196 : 11 : static __init int intel_epb_init(void)
197 : : {
198 : 11 : int ret;
199 : :
200 [ - + ]: 11 : if (!boot_cpu_has(X86_FEATURE_EPB))
201 : : return -ENODEV;
202 : :
203 : 0 : ret = cpuhp_setup_state(CPUHP_AP_X86_INTEL_EPB_ONLINE,
204 : : "x86/intel/epb:online", intel_epb_online,
205 : : intel_epb_offline);
206 [ # # ]: 0 : if (ret < 0)
207 : 0 : goto err_out_online;
208 : :
209 : 0 : register_syscore_ops(&intel_epb_syscore_ops);
210 : 0 : return 0;
211 : :
212 : : err_out_online:
213 : 0 : cpuhp_remove_state(CPUHP_AP_X86_INTEL_EPB_ONLINE);
214 : 0 : return ret;
215 : : }
216 : : subsys_initcall(intel_epb_init);
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