drivers/cpufreq/virtual-cpufreq.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2024 Google LLC
   4  */
   5
   6 #include <linux/arch_topology.h>
   7 #include <linux/cpufreq.h>
   8 #include <linux/init.h>
   9 #include <linux/sched.h>
  10 #include <linux/kernel.h>
  11 #include <linux/module.h>
  12 #include <linux/of_address.h>
  13 #include <linux/of_platform.h>
  14 #include <linux/platform_device.h>
  15 #include <linux/slab.h>
  16
  17 /*
  18  * CPU0..CPUn
  19  * +-------------+-------------------------------+--------+-------+
  20  * | Register    | Description                   | Offset |   Len |
  21  * +-------------+-------------------------------+--------+-------+
  22  * | cur_perf    | read this register to get     |    0x0 |   0x4 |
  23  * |             | the current perf (integer val |        |       |
  24  * |             | representing perf relative to |        |       |
  25  * |             | max performance)              |        |       |
  26  * |             | that vCPU is running at       |        |       |
  27  * +-------------+-------------------------------+--------+-------+
  28  * | set_perf    | write to this register to set |    0x4 |   0x4 |
  29  * |             | perf value of the vCPU        |        |       |
  30  * +-------------+-------------------------------+--------+-------+
  31  * | perftbl_len | number of entries in perf     |    0x8 |   0x4 |
  32  * |             | table. A single entry in the  |        |       |
  33  * |             | perf table denotes no table   |        |       |
  34  * |             | and the entry contains        |        |       |
  35  * |             | the maximum perf value        |        |       |
  36  * |             | that this vCPU supports.      |        |       |
  37  * |             | The guest can request any     |        |       |
  38  * |             | value between 1 and max perf  |        |       |
  39  * |             | when perftbls are not used.   |        |       |
  40  * +---------------------------------------------+--------+-------+
  41  * | perftbl_sel | write to this register to     |    0xc |   0x4 |
  42  * |             | select perf table entry to    |        |       |
  43  * |             | read from                     |        |       |
  44  * +---------------------------------------------+--------+-------+
  45  * | perftbl_rd  | read this register to get     |   0x10 |   0x4 |
  46  * |             | perf value of the selected    |        |       |
  47  * |             | entry based on perftbl_sel    |        |       |
  48  * +---------------------------------------------+--------+-------+
  49  * | perf_domain | performance domain number     |   0x14 |   0x4 |
  50  * |             | that this vCPU belongs to.    |        |       |
  51  * |             | vCPUs sharing the same perf   |        |       |
  52  * |             | domain number are part of the |        |       |
  53  * |             | same performance domain.      |        |       |
  54  * +-------------+-------------------------------+--------+-------+
  55  */
  56
  57 #define REG_CUR_PERF_STATE_OFFSET 0x0
  58 #define REG_SET_PERF_STATE_OFFSET 0x4
  59 #define REG_PERFTBL_LEN_OFFSET 0x8
  60 #define REG_PERFTBL_SEL_OFFSET 0xc
  61 #define REG_PERFTBL_RD_OFFSET 0x10
  62 #define REG_PERF_DOMAIN_OFFSET 0x14
  63 #define PER_CPU_OFFSET 0x1000
  64
  65 #define PERFTBL_MAX_ENTRIES 64U
  66
  67 static void __iomem *base;
  68 static DEFINE_PER_CPU(u32, perftbl_num_entries);
  69
  70 static void virt_scale_freq_tick(void)
  71 {
  72         int cpu = smp_processor_id();
  73         u32 max_freq = (u32)cpufreq_get_hw_max_freq(cpu);
  74         u64 cur_freq;
  75         unsigned long scale;
  76
  77         cur_freq = (u64)readl_relaxed(base + cpu * PER_CPU_OFFSET
  78                         + REG_CUR_PERF_STATE_OFFSET);
  79
  80         cur_freq <<= SCHED_CAPACITY_SHIFT;
  81         scale = (unsigned long)div_u64(cur_freq, max_freq);
  82         scale = min(scale, SCHED_CAPACITY_SCALE);
  83
  84         this_cpu_write(arch_freq_scale, scale);
  85 }
  86
  87 static struct scale_freq_data virt_sfd = {
  88         .source = SCALE_FREQ_SOURCE_VIRT,
  89         .set_freq_scale = virt_scale_freq_tick,
  90 };
  91
  92 static unsigned int virt_cpufreq_set_perf(struct cpufreq_policy *policy,
  93                                           unsigned int target_freq)
  94 {
  95         writel_relaxed(target_freq,
  96                        base + policy->cpu * PER_CPU_OFFSET + REG_SET_PERF_STATE_OFFSET);
  97         return 0;
  98 }
  99
 100 static unsigned int virt_cpufreq_fast_switch(struct cpufreq_policy *policy,
 101                                              unsigned int target_freq)
 102 {
 103         virt_cpufreq_set_perf(policy, target_freq);
 104         return target_freq;
 105 }
 106
 107 static u32 virt_cpufreq_get_perftbl_entry(int cpu, u32 idx)
 108 {
 109         writel_relaxed(idx, base + cpu * PER_CPU_OFFSET +
 110                        REG_PERFTBL_SEL_OFFSET);
 111         return readl_relaxed(base + cpu * PER_CPU_OFFSET +
 112                              REG_PERFTBL_RD_OFFSET);
 113 }
 114
 115 static int virt_cpufreq_target(struct cpufreq_policy *policy,
 116                                unsigned int target_freq,
 117                                unsigned int relation)
 118 {
 119         struct cpufreq_freqs freqs;
 120         int ret = 0;
 121
 122         freqs.old = policy->cur;
 123         freqs.new = target_freq;
 124
 125         cpufreq_freq_transition_begin(policy, &freqs);
 126         ret = virt_cpufreq_set_perf(policy, target_freq);
 127         cpufreq_freq_transition_end(policy, &freqs, ret != 0);
 128
 129         return ret;
 130 }
 131
 132 static int virt_cpufreq_get_sharing_cpus(struct cpufreq_policy *policy)
 133 {
 134         u32 cur_perf_domain, perf_domain;
 135         struct device *cpu_dev;
 136         int cpu;
 137
 138         cur_perf_domain = readl_relaxed(base + policy->cpu *
 139                                         PER_CPU_OFFSET + REG_PERF_DOMAIN_OFFSET);
 140
 141         for_each_possible_cpu(cpu) {
 142                 cpu_dev = get_cpu_device(cpu);
 143                 if (!cpu_dev)
 144                         continue;
 145
 146                 perf_domain = readl_relaxed(base + cpu *
 147                                             PER_CPU_OFFSET + REG_PERF_DOMAIN_OFFSET);
 148
 149                 if (perf_domain == cur_perf_domain)
 150                         cpumask_set_cpu(cpu, policy->cpus);
 151         }
 152
 153         return 0;
 154 }
 155
 156 static int virt_cpufreq_get_freq_info(struct cpufreq_policy *policy)
 157 {
 158         struct cpufreq_frequency_table *table;
 159         u32 num_perftbl_entries, idx;
 160
 161         num_perftbl_entries = per_cpu(perftbl_num_entries, policy->cpu);
 162
 163         if (num_perftbl_entries == 1) {
 164                 policy->cpuinfo.min_freq = 1;
 165                 policy->cpuinfo.max_freq = virt_cpufreq_get_perftbl_entry(policy->cpu, 0);
 166
 167                 policy->min = policy->cpuinfo.min_freq;
 168                 policy->max = policy->cpuinfo.max_freq;
 169
 170                 policy->cur = policy->max;
 171                 return 0;
 172         }
 173
 174         table = kcalloc(num_perftbl_entries + 1, sizeof(*table), GFP_KERNEL);
 175         if (!table)
 176                 return -ENOMEM;
 177
 178         for (idx = 0; idx < num_perftbl_entries; idx++)
 179                 table[idx].frequency = virt_cpufreq_get_perftbl_entry(policy->cpu, idx);
 180
 181         table[idx].frequency = CPUFREQ_TABLE_END;
 182         policy->freq_table = table;
 183
 184         return 0;
 185 }
 186
 187 static int virt_cpufreq_cpu_init(struct cpufreq_policy *policy)
 188 {
 189         struct device *cpu_dev;
 190         int ret;
 191
 192         cpu_dev = get_cpu_device(policy->cpu);
 193         if (!cpu_dev)
 194                 return -ENODEV;
 195
 196         ret = virt_cpufreq_get_freq_info(policy);
 197         if (ret) {
 198                 dev_warn(cpu_dev, "failed to get cpufreq info\n");
 199                 return ret;
 200         }
 201
 202         ret = virt_cpufreq_get_sharing_cpus(policy);
 203         if (ret) {
 204                 dev_warn(cpu_dev, "failed to get sharing cpumask\n");
 205                 return ret;
 206         }
 207
 208         /*
 209          * To simplify and improve latency of handling frequency requests on
 210          * the host side, this ensures that the vCPU thread triggering the MMIO
 211          * abort is the same thread whose performance constraints (Ex. uclamp
 212          * settings) need to be updated. This simplifies the VMM (Virtual
 213          * Machine Manager) having to find the correct vCPU thread and/or
 214          * facing permission issues when configuring other threads.
 215          */
 216         policy->dvfs_possible_from_any_cpu = false;
 217         policy->fast_switch_possible = true;
 218
 219         /*
 220          * Using the default SCALE_FREQ_SOURCE_CPUFREQ is insufficient since
 221          * the actual physical CPU frequency may not match requested frequency
 222          * from the vCPU thread due to frequency update latencies or other
 223          * inputs to the physical CPU frequency selection. This additional FIE
 224          * source allows for more accurate freq_scale updates and only takes
 225          * effect if another FIE source such as AMUs have not been registered.
 226          */
 227         topology_set_scale_freq_source(&virt_sfd, policy->cpus);
 228
 229         return 0;
 230 }
 231
 232 static void virt_cpufreq_cpu_exit(struct cpufreq_policy *policy)
 233 {
 234         topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_VIRT, policy->related_cpus);
 235         kfree(policy->freq_table);
 236 }
 237
 238 static int virt_cpufreq_online(struct cpufreq_policy *policy)
 239 {
 240         /* Nothing to restore. */
 241         return 0;
 242 }
 243
 244 static int virt_cpufreq_offline(struct cpufreq_policy *policy)
 245 {
 246         /* Dummy offline() to avoid exit() being called and freeing resources. */
 247         return 0;
 248 }
 249
 250 static int virt_cpufreq_verify_policy(struct cpufreq_policy_data *policy)
 251 {
 252         if (policy->freq_table)
 253                 return cpufreq_frequency_table_verify(policy, policy->freq_table);
 254
 255         cpufreq_verify_within_cpu_limits(policy);
 256         return 0;
 257 }
 258
 259 static struct cpufreq_driver cpufreq_virt_driver = {
 260         .name           = "virt-cpufreq",
 261         .init           = virt_cpufreq_cpu_init,
 262         .exit           = virt_cpufreq_cpu_exit,
 263         .online         = virt_cpufreq_online,
 264         .offline        = virt_cpufreq_offline,
 265         .verify         = virt_cpufreq_verify_policy,
 266         .target         = virt_cpufreq_target,
 267         .fast_switch    = virt_cpufreq_fast_switch,
 268         .attr           = cpufreq_generic_attr,
 269 };
 270
 271 static int virt_cpufreq_driver_probe(struct platform_device *pdev)
 272 {
 273         u32 num_perftbl_entries;
 274         int ret, cpu;
 275
 276         base = devm_platform_ioremap_resource(pdev, 0);
 277         if (IS_ERR(base))
 278                 return PTR_ERR(base);
 279
 280         for_each_possible_cpu(cpu) {
 281                 num_perftbl_entries = readl_relaxed(base + cpu * PER_CPU_OFFSET +
 282                                                     REG_PERFTBL_LEN_OFFSET);
 283
 284                 if (!num_perftbl_entries || num_perftbl_entries > PERFTBL_MAX_ENTRIES)
 285                         return -ENODEV;
 286
 287                 per_cpu(perftbl_num_entries, cpu) = num_perftbl_entries;
 288         }
 289
 290         ret = cpufreq_register_driver(&cpufreq_virt_driver);
 291         if (ret) {
 292                 dev_err(&pdev->dev, "Virtual CPUFreq driver failed to register: %d\n", ret);
 293                 return ret;
 294         }
 295
 296         dev_dbg(&pdev->dev, "Virtual CPUFreq driver initialized\n");
 297         return 0;
 298 }
 299
 300 static void virt_cpufreq_driver_remove(struct platform_device *pdev)
 301 {
 302         cpufreq_unregister_driver(&cpufreq_virt_driver);
 303 }
 304
 305 static const struct of_device_id virt_cpufreq_match[] = {
 306         { .compatible = "qemu,virtual-cpufreq", .data = NULL},
 307         {}
 308 };
 309 MODULE_DEVICE_TABLE(of, virt_cpufreq_match);
 310
 311 static struct platform_driver virt_cpufreq_driver = {
 312         .probe = virt_cpufreq_driver_probe,
 313         .remove = virt_cpufreq_driver_remove,
 314         .driver = {
 315                 .name = "virt-cpufreq",
 316                 .of_match_table = virt_cpufreq_match,
 317         },
 318 };
 319
 320 static int __init virt_cpufreq_init(void)
 321 {
 322         return platform_driver_register(&virt_cpufreq_driver);
 323 }
 324 postcore_initcall(virt_cpufreq_init);
 325
 326 static void __exit virt_cpufreq_exit(void)
 327 {
 328         platform_driver_unregister(&virt_cpufreq_driver);
 329 }
 330 module_exit(virt_cpufreq_exit);
 331
 332 MODULE_DESCRIPTION("Virtual cpufreq driver");
 333 MODULE_LICENSE("GPL");