[PATCH V8 14/14] cpufreq: Add Rust based cpufreq-dt driver

Viresh Kumar
2025-02-06T09:29:47Z

This commit adds a Rust based cpufreq-dt driver, which covers most of
the functionality of the existing C based driver. Only a handful of
things are left, like fetching platform data from cpufreq-dt-platdev.c.

This is tested with the help of QEMU for now and switching of
frequencies work as expected.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
drivers/cpufreq/Kconfig | 12 ++
drivers/cpufreq/Makefile | 1 +
drivers/cpufreq/rcpufreq_dt.rs | 238 +++++++++++++++++++++++++++++++++
rust/kernel/cpufreq.rs | 10 +-
4 files changed, 257 insertions(+), 4 deletions(-)
create mode 100644 drivers/cpufreq/rcpufreq_dt.rs

diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
index d64b07ec48e5..78702a08364f 100644
--- a/drivers/cpufreq/Kconfig
+++ b/drivers/cpufreq/Kconfig
@@ -217,6 +217,18 @@ config CPUFREQ_DT

If in doubt, say N.

+config CPUFREQ_DT_RUST
+ tristate "Rust based Generic DT based cpufreq driver"
+ depends on HAVE_CLK && OF && RUST
+ select CPUFREQ_DT_PLATDEV
+ select PM_OPP
+ help
+ This adds a Rust based generic DT based cpufreq driver for frequency
+ management. It supports both uniprocessor (UP) and symmetric
+ multiprocessor (SMP) systems.
+
+ If in doubt, say N.
+
config CPUFREQ_VIRT
tristate "Virtual cpufreq driver"
depends on GENERIC_ARCH_TOPOLOGY
diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
index 890fff99f37d..7fa29bdec3c7 100644
--- a/drivers/cpufreq/Makefile
+++ b/drivers/cpufreq/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_CPU_FREQ_GOV_COMMON) += cpufreq_governor.o
obj-$(CONFIG_CPU_FREQ_GOV_ATTR_SET) += cpufreq_governor_attr_set.o

obj-$(CONFIG_CPUFREQ_DT) += cpufreq-dt.o
+obj-$(CONFIG_CPUFREQ_DT_RUST) += rcpufreq_dt.o
obj-$(CONFIG_CPUFREQ_DT_PLATDEV) += cpufreq-dt-platdev.o
obj-$(CONFIG_CPUFREQ_VIRT) += virtual-cpufreq.o

diff --git a/drivers/cpufreq/rcpufreq_dt.rs b/drivers/cpufreq/rcpufreq_dt.rs
new file mode 100644
index 000000000000..461e88006ed9
--- /dev/null
+++ b/drivers/cpufreq/rcpufreq_dt.rs
@@ -0,0 +1,238 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust based implementation of the cpufreq-dt driver.
+
+use core::format_args;
+
+use kernel::{
+ c_str, clk, cpu, cpufreq, cpumask::Cpumask, device::Device, error::code::*, fmt,
+ macros::vtable, module_platform_driver, of, opp, platform, prelude::*, str::CString, sync::Arc,
+};
+
+// Finds exact supply name from the OF node.
+fn find_supply_name_exact(dev: &Device, name: &str) -> Option<CString> {
+ let name_cstr = CString::try_from_fmt(fmt!("{}-supply", name)).ok()?;
+
+ if dev.property_present(&name_cstr) {
+ CString::try_from_fmt(fmt!("{}", name)).ok()
+ } else {
+ None
+ }
+}
+
+// Finds supply name for the CPU from DT.
+fn find_supply_names(dev: &Device, cpu: u32) -> Option<KVec<CString>> {
+ // Try "cpu0" for older DTs.
+ let name = match cpu {
+ 0 => find_supply_name_exact(dev, "cpu0"),
+ _ => None,
+ }
+ .or(find_supply_name_exact(dev, "cpu"))?;
+
+ let mut list = KVec::with_capacity(1, GFP_KERNEL).ok()?;
+ list.push(name, GFP_KERNEL).ok()?;
+
+ Some(list)
+}
+
+// Represents the cpufreq dt device.
+struct CPUFreqDTDevice {
+ opp_table: opp::Table,
+ freq_table: opp::FreqTable,
+ #[allow(dead_code)]
+ mask: Cpumask,
+ #[allow(dead_code)]
+ token: Option<opp::ConfigToken>,
+ #[allow(dead_code)]
+ clk: clk::Clk,
+}
+
+struct CPUFreqDTDriver {
+ _pdev: platform::Device,
+}
+
+#[vtable]
+impl opp::ConfigOps for CPUFreqDTDriver {}
+
+#[vtable]
+impl cpufreq::Driver for CPUFreqDTDriver {
+ type Data = ();
+ type PData = Arc<CPUFreqDTDevice>;
+
+ fn init(policy: &mut cpufreq::Policy) -> Result<Self::PData> {
+ let cpu = policy.cpu();
+ // SAFETY: The CPU device is only used from the init() callback during which the CPU can't
+ // get hot-unplugged. Also the cpufreq core in C library, registers with CPU notifiers and
+ // the cpufreq core/driver won't use the CPU device, once the CPU is hot-unplugged.
+ let dev = unsafe { cpu::from_cpu(cpu)? };
+ let mut mask = Cpumask::new()?;
+
+ mask.set(cpu);
+
+ let token = match find_supply_names(dev, cpu) {
+ Some(names) => Some(
+ opp::Config::<Self>::new()
+ .set_regulator_names(names)?
+ .set(dev)?,
+ ),
+ _ => None,
+ };
+
+ // Get OPP-sharing information from "operating-points-v2" bindings.
+ let fallback = match opp::Table::of_sharing_cpus(dev, &mut mask) {
+ Ok(()) => false,
+ Err(e) => {
+ if e != ENOENT {
+ return Err(e);
+ }
+
+ // "operating-points-v2" not supported. If the platform hasn't
+ // set sharing CPUs, fallback to all CPUs share the `Policy`
+ // for backward compatibility.
+ opp::Table::sharing_cpus(dev, &mut mask).is_err()
+ }
+ };
+
+ // Initialize OPP tables for all policy cpus.
+ //
+ // For platforms not using "operating-points-v2" bindings, we do this
+ // before updating policy cpus. Otherwise, we will end up creating
+ // duplicate OPPs for the CPUs.
+ //
+ // OPPs might be populated at runtime, don't fail for error here unless
+ // it is -EPROBE_DEFER.
+ let mut opp_table = match opp::Table::from_of_cpumask(dev, &mut mask) {
+ Ok(table) => table,
+ Err(e) => {
+ if e == EPROBE_DEFER {
+ return Err(e);
+ }
+
+ // The table is added dynamically ?
+ opp::Table::from_dev(dev)?
+ }
+ };
+
+ // The OPP table must be initialized, statically or dynamically, by this point.
+ opp_table.opp_count()?;
+
+ // Set sharing cpus for fallback scenario.
+ if fallback {
+ mask.set_all();
+ opp_table.set_sharing_cpus(&mut mask)?;
+ }
+
+ let mut transition_latency = opp_table.max_transition_latency() as u32;
+ if transition_latency == 0 {
+ transition_latency = cpufreq::ETERNAL_LATENCY;
+ }
+
+ let freq_table = opp_table.to_cpufreq_table()?;
+ let clk = policy
+ .set_freq_table(freq_table.table())
+ .set_dvfs_possible_from_any_cpu()
+ .set_suspend_freq((opp_table.suspend_freq() / 1000) as u32)
+ .set_transition_latency(transition_latency)
+ .set_clk(dev, None)?;
+
+ mask.copy(policy.cpus());
+
+ Ok(Arc::new(
+ CPUFreqDTDevice {
+ opp_table,
+ freq_table,
+ mask,
+ token,
+ clk,
+ },
+ GFP_KERNEL,
+ )?)
+ }
+
+ fn exit(_policy: &mut cpufreq::Policy, _data: Option<Self::PData>) -> Result<()> {
+ Ok(())
+ }
+
+ fn online(_policy: &mut cpufreq::Policy) -> Result<()> {
+ // We did light-weight tear down earlier, nothing to do here.
+ Ok(())
+ }
+
+ fn offline(_policy: &mut cpufreq::Policy) -> Result<()> {
+ // Preserve policy->data and don't free resources on light-weight
+ // tear down.
+ Ok(())
+ }
+
+ fn suspend(policy: &mut cpufreq::Policy) -> Result<()> {
+ policy.generic_suspend()
+ }
+
+ fn verify(data: &mut cpufreq::PolicyData) -> Result<()> {
+ data.generic_verify()
+ }
+
+ fn target_index(policy: &mut cpufreq::Policy, index: u32) -> Result<()> {
+ let data = match policy.data::<Self::PData>() {
+ Some(data) => data,
+ None => return Err(ENOENT),
+ };
+
+ let freq = data.freq_table.freq(index.try_into().unwrap())? as usize;
+ data.opp_table.set_rate(freq * 1000)
+ }
+
+ fn get(policy: &mut cpufreq::Policy) -> Result<u32> {
+ policy.generic_get()
+ }
+
+ fn set_boost(_policy: &mut cpufreq::Policy, _state: i32) -> Result<()> {
+ Ok(())
+ }
+
+ fn register_em(policy: &mut cpufreq::Policy) {
+ policy.register_em_opp()
+ }
+}
+
+kernel::of_device_table!(
+ OF_TABLE,
+ MODULE_OF_TABLE,
+ <CPUFreqDTDriver as platform::Driver>::IdInfo,
+ [(of::DeviceId::new(c_str!("operating-points-v2")), ())]
+);
+
+impl platform::Driver for CPUFreqDTDriver {
+ type IdInfo = ();
+ const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
+
+ fn probe(
+ pdev: &mut platform::Device,
+ _id_info: Option<&Self::IdInfo>,
+ ) -> Result<Pin<KBox<Self>>> {
+ cpufreq::Registration::<CPUFreqDTDriver>::new_foreign_owned(
+ pdev.as_ref(),
+ c_str!("cpufreq-dt"),
+ (),
+ cpufreq::flags::NEED_INITIAL_FREQ_CHECK | cpufreq::flags::IS_COOLING_DEV,
+ true,
+ )?;
+
+ let drvdata = KBox::new(
+ Self {
+ _pdev: pdev.clone(),
+ },
+ GFP_KERNEL,
+ )?;
+
+ Ok(drvdata.into())
+ }
+}
+
+module_platform_driver! {
+ type: CPUFreqDTDriver,
+ name: "cpufreq-dt",
+ author: "Viresh Kumar <viresh.kumar@linaro.org>",
+ description: "Generic CPUFreq DT driver",
+ license: "GPL v2",
+}
diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
index f92259d339d3..ecf7c6e2cb89 100644
--- a/rust/kernel/cpufreq.rs
+++ b/rust/kernel/cpufreq.rs
@@ -628,15 +628,17 @@ pub fn new(name: &'static CStr, data: T::Data, flags: u16, boost: bool) -> Resul

// SAFETY: The C code returns a valid pointer here, which is again passed to the C code in
// an array.
- attr[next] =
- unsafe { addr_of_mut!(bindings::cpufreq_freq_attr_scaling_available_freqs) as *mut _ };
+ attr[next] = unsafe {
+ addr_of_mut!(bindings::cpufreq_freq_attr_scaling_available_freqs) as *mut _
+ };
next += 1;

if boost {
// SAFETY: The C code returns a valid pointer here, which is again passed to the C code
// in an array.
- attr[next] =
- unsafe { addr_of_mut!(bindings::cpufreq_freq_attr_scaling_boost_freqs) as *mut _ };
+ attr[next] = unsafe {
+ addr_of_mut!(bindings::cpufreq_freq_attr_scaling_boost_freqs) as *mut _
+ };
next += 1;
}
attr[next] = ptr::null_mut();
--
2.31.1.272.g89b43f80a514