[RFC PATCH 28/31] xen/arm: Introduce SCPI based CPUFreq driver

[Oleksandr Tyshchenko <olekstysh@gmail.com>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

This patch adds a CPUFreq driver for controlling CPUs DVFS feature
provided by System Control Processor (SCP) using SCPI protocol
for inter-processor communication.

The important point is that unlike Linux Xen doesn't have
clock infrastructure and clocks for the CPUs (DVFS clocks)
provided by SCP are managed by this driver directly using
DVFS operations over power domains the controlled CPUs are part of.

Non-arch specific driver code is mostly borrowed from
the x86 ACPI CPUFreq.

Most important TODOs regarding the whole patch series:
1. Handle devm in the direct ported code. Currently, in case of any
   errors previously allocated resources are left unfreed.
2. Thermal management integration.
3. Don't pass CPUFreq related nodes to dom0. Xen owns SCPI completely.
4. Handle CPU_TURBO frequencies.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien.grall@linaro.org>
---
 xen/arch/arm/cpufreq/scpi_cpufreq.c | 328 ++++++++++++++++++++++++++++++++++++
 1 file changed, 328 insertions(+)
 create mode 100644 xen/arch/arm/cpufreq/scpi_cpufreq.c

diff --git a/xen/arch/arm/cpufreq/scpi_cpufreq.c b/xen/arch/arm/cpufreq/scpi_cpufreq.c
new file mode 100644
index 0000000..bcd8889
--- /dev/null
+++ b/xen/arch/arm/cpufreq/scpi_cpufreq.c
@@ -0,0 +1,328 @@
+/*
+ * xen/arch/arm/cpufreq/scpi_cpufreq.c
+ *
+ * SCPI based CPUFreq driver
+ *
+ * Based on Xen arch/x86/acpi/cpufreq/cpufreq.c
+ *
+ * Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
+ * Copyright (c) 2017 EPAM Systems.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <xen/types.h>
+#include <xen/delay.h>
+#include <xen/cpumask.h>
+#include <xen/sched.h>
+#include <xen/xmalloc.h>
+#include <xen/err.h>
+#include <xen/cpufreq.h>
+#include <asm/bug.h>
+#include <asm/percpu.h>
+
+#include "scpi_protocol.h"
+
+extern struct device *get_cpu_device(unsigned int cpu);
+
+struct scpi_cpufreq_data
+{
+    struct processor_performance *perf;
+    struct cpufreq_frequency_table *freq_table;
+    struct scpi_dvfs_info *info; /* DVFS capabilities of the CPU's power domain */
+    int domain; /* power domain id this CPU belongs to */
+};
+
+static struct scpi_cpufreq_data *cpufreq_driver_data[NR_CPUS];
+
+static struct cpufreq_driver scpi_cpufreq_driver;
+
+static struct scpi_ops *scpi_ops;
+
+static unsigned int scpi_cpufreq_get(unsigned int cpu)
+{
+    struct scpi_cpufreq_data *data;
+    struct cpufreq_policy *policy;
+    const struct scpi_opp *opp;
+    int idx;
+
+    if ( cpu >= nr_cpu_ids || !cpu_online(cpu) )
+        return 0;
+
+    policy = per_cpu(cpufreq_cpu_policy, cpu);
+    if ( !policy || !(data = cpufreq_driver_data[policy->cpu]) ||
+         !data->info )
+        return 0;
+
+    idx = scpi_ops->dvfs_get_idx(data->domain);
+    if ( idx < 0 )
+        return 0;
+
+    opp = data->info->opps + idx;
+
+    /* Convert Hz -> kHz */
+    return opp->freq / 1000;
+}
+
+static int scpi_cpufreq_target(struct cpufreq_policy *policy,
+                               unsigned int target_freq, unsigned int relation)
+{
+    struct scpi_cpufreq_data *data = cpufreq_driver_data[policy->cpu];
+    struct processor_performance *perf;
+    struct cpufreq_freqs freqs;
+    cpumask_t online_policy_cpus;
+    unsigned int next_state = 0; /* Index into freq_table */
+    unsigned int next_perf_state = 0; /* Index into perf table */
+    unsigned int j;
+    int result;
+    const struct scpi_opp *opp;
+    int idx, max_opp;
+
+    if ( unlikely(!data) || !data->perf || !data->freq_table || !data->info )
+        return -ENODEV;
+
+    perf = data->perf;
+    result = cpufreq_frequency_table_target(policy,
+                                            data->freq_table,
+                                            target_freq,
+                                            relation, &next_state);
+    if ( unlikely(result) )
+        return -ENODEV;
+
+    cpumask_and(&online_policy_cpus, &cpu_online_map, policy->cpus);
+
+    next_perf_state = data->freq_table[next_state].index;
+    if ( perf->state == next_perf_state )
+    {
+        if ( unlikely(policy->resume) )
+            policy->resume = 0;
+        else
+            return 0;
+    }
+
+    /* Convert MHz -> kHz */
+    freqs.old = perf->states[perf->state].core_frequency * 1000;
+    freqs.new = data->freq_table[next_state].frequency;
+
+    /* Find corresponding index */
+    max_opp = data->info->count;
+    opp = data->info->opps;
+    for ( idx = 0; idx < max_opp; idx++, opp++ )
+    {
+        /* Compare in kHz */
+        if ( opp->freq / 1000 == freqs.new )
+            break;
+    }
+    if ( idx == max_opp )
+        return -EINVAL;
+
+    result = scpi_ops->dvfs_set_idx(data->domain, idx);
+    if ( result < 0 )
+        return result;
+
+    for_each_cpu( j, &online_policy_cpus )
+        cpufreq_statistic_update(j, perf->state, next_perf_state);
+
+    perf->state = next_perf_state;
+    policy->cur = freqs.new;
+
+    return result;
+}
+
+static int scpi_cpufreq_verify(struct cpufreq_policy *policy)
+{
+    struct scpi_cpufreq_data *data;
+    struct processor_performance *perf;
+
+    if ( !policy || !(data = cpufreq_driver_data[policy->cpu]) ||
+         !processor_pminfo[policy->cpu] )
+        return -EINVAL;
+
+    perf = &processor_pminfo[policy->cpu]->perf;
+
+    /* Convert MHz -> kHz */
+    cpufreq_verify_within_limits(policy, 0,
+        perf->states[perf->platform_limit].core_frequency * 1000);
+
+    return cpufreq_frequency_table_verify(policy, data->freq_table);
+}
+
+static int scpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
+{
+    unsigned int i;
+    unsigned int valid_states = 0;
+    unsigned int curr_state, curr_freq;
+    struct scpi_cpufreq_data *data;
+    int result;
+    struct processor_performance *perf;
+    struct device *cpu_dev;
+    struct scpi_dvfs_info *info;
+    int domain;
+
+    cpu_dev = get_cpu_device(policy->cpu);
+    if ( !cpu_dev )
+        return -ENODEV;
+
+    data = xzalloc(struct scpi_cpufreq_data);
+    if ( !data )
+        return -ENOMEM;
+
+    cpufreq_driver_data[policy->cpu] = data;
+
+    data->perf = &processor_pminfo[policy->cpu]->perf;
+
+    perf = data->perf;
+    policy->shared_type = perf->shared_type;
+
+    data->freq_table = xmalloc_array(struct cpufreq_frequency_table,
+                                    (perf->state_count + 1));
+    if ( !data->freq_table )
+    {
+        result = -ENOMEM;
+        goto err_unreg;
+    }
+
+    /* Detect transition latency */
+    policy->cpuinfo.transition_latency = 0;
+    for ( i = 0; i < perf->state_count; i++ )
+    {
+        /* Compare in ns */
+        if ( perf->states[i].transition_latency * 1000 >
+             policy->cpuinfo.transition_latency )
+            /* Convert us -> ns */
+            policy->cpuinfo.transition_latency =
+                perf->states[i].transition_latency * 1000;
+    }
+
+    policy->governor = cpufreq_opt_governor ? : CPUFREQ_DEFAULT_GOVERNOR;
+
+    /* Initialize frequency table */
+    for ( i = 0; i < perf->state_count; i++ )
+    {
+        /* Compare in MHz */
+        if ( i > 0 && perf->states[i].core_frequency >=
+             data->freq_table[valid_states - 1].frequency / 1000 )
+            continue;
+
+        data->freq_table[valid_states].index = i;
+        /* Convert MHz -> kHz */
+        data->freq_table[valid_states].frequency =
+            perf->states[i].core_frequency * 1000;
+        valid_states++;
+    }
+    data->freq_table[valid_states].frequency = CPUFREQ_TABLE_END;
+    perf->state = 0;
+
+    result = cpufreq_frequency_table_cpuinfo(policy, data->freq_table);
+    if ( result )
+        goto err_freqfree;
+
+    /* Fill in fields needed for frequency changing */
+    domain = scpi_ops->device_domain_id(cpu_dev);
+    if ( domain < 0 )
+    {
+        result = domain;
+        goto err_freqfree;
+    }
+    data->domain = domain;
+
+    info = scpi_ops->dvfs_get_info(domain);
+    if ( IS_ERR(info) )
+    {
+        result = PTR_ERR(info);
+        goto err_freqfree;
+    }
+    data->info = info;
+
+    /* Retrieve current frequency */
+    curr_freq = scpi_cpufreq_get(policy->cpu);
+
+    /* Find corresponding state */
+    curr_state = 0;
+    for ( i = 0; data->freq_table[i].frequency != CPUFREQ_TABLE_END; i++ )
+    {
+        if ( curr_freq == data->freq_table[i].frequency )
+        {
+            curr_state = i;
+            break;
+        }
+    }
+
+    /* Update fields with actual values */
+    policy->cur = curr_freq;
+    perf->state = data->freq_table[curr_state].index;
+
+    /*
+     * the first call to ->target() should result in us actually
+     * writing something to the appropriate registers.
+     */
+    policy->resume = 1;
+
+    return result;
+
+err_freqfree:
+    xfree(data->freq_table);
+err_unreg:
+    xfree(data);
+    cpufreq_driver_data[policy->cpu] = NULL;
+
+    return result;
+}
+
+static int scpi_cpufreq_cpu_exit(struct cpufreq_policy *policy)
+{
+    struct scpi_cpufreq_data *data = cpufreq_driver_data[policy->cpu];
+
+    if ( data )
+    {
+        xfree(data->freq_table);
+        xfree(data);
+        cpufreq_driver_data[policy->cpu] = NULL;
+    }
+
+    return 0;
+}
+
+static struct cpufreq_driver scpi_cpufreq_driver = {
+    .name   = "scpi-cpufreq",
+
+    .verify = scpi_cpufreq_verify,
+    .target = scpi_cpufreq_target,
+    .get    = scpi_cpufreq_get,
+    .init   = scpi_cpufreq_cpu_init,
+    .exit   = scpi_cpufreq_cpu_exit,
+};
+
+int __init scpi_cpufreq_register_driver(void)
+{
+    scpi_ops = get_scpi_ops();
+    if ( !scpi_ops )
+        return -ENXIO;
+
+    return cpufreq_register_driver(&scpi_cpufreq_driver);
+}
+
+int cpufreq_cpu_init(unsigned int cpuid)
+{
+    return cpufreq_add_cpu(cpuid);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
-- 
2.7.4


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