[RFC PATCH V3 6/8] rust: Extend cpufreq bindings for driver registration

[Viresh Kumar <viresh.kumar@linaro.org>]

This extends the cpufreq bindings with bindings for registering a
driver.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 rust/kernel/cpufreq.rs | 482 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 479 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
index 6f9d34ebbcb0..66dad18f4ab6 100644
--- a/rust/kernel/cpufreq.rs
+++ b/rust/kernel/cpufreq.rs
@@ -9,14 +9,16 @@
 use crate::{
     bindings, clk, cpumask,
     device::Device,
-    error::{code::*, from_err_ptr, to_result, Result, VTABLE_DEFAULT_ERROR},
+    error::{code::*, from_err_ptr, from_result, to_result, Result, VTABLE_DEFAULT_ERROR},
     prelude::*,
-    types::{ARef, ForeignOwnable},
+    types::ForeignOwnable,
 };
 
 use core::{
+    cell::UnsafeCell,
+    marker::PhantomData,
     pin::Pin,
-    ptr::self,
+    ptr::{self, addr_of_mut},
 };
 
 use macros::vtable;
@@ -563,3 +565,477 @@ fn register_em(_policy: &mut Policy) {
         kernel::build_error(VTABLE_DEFAULT_ERROR)
     }
 }
+
+/// Registration of a cpufreq driver.
+pub struct Registration<T: Driver> {
+    registered: bool,
+    drv: UnsafeCell<bindings::cpufreq_driver>,
+    _p: PhantomData<T>,
+}
+
+// SAFETY: `Registration` doesn't offer any methods or access to fields when shared between threads
+// or CPUs, so it is safe to share it.
+unsafe impl<T: Driver> Sync for Registration<T> {}
+
+// SAFETY: Registration with and unregistration from the cpufreq subsystem can happen from any thread.
+// Additionally, `T::Data` (which is dropped during unregistration) is `Send`, so it is okay to move
+// `Registration` to different threads.
+#[allow(clippy::non_send_fields_in_send_ty)]
+unsafe impl<T: Driver> Send for Registration<T> {}
+
+impl<T: Driver> Registration<T> {
+    /// Creates new [`Registration`] but does not register it yet.
+    ///
+    /// It is allowed to move.
+    fn new() -> Result<Box<Self>> {
+        Ok(Box::new(
+            Self {
+                registered: false,
+                drv: UnsafeCell::new(bindings::cpufreq_driver::default()),
+                _p: PhantomData,
+            },
+            GFP_KERNEL,
+        )?)
+    }
+
+    /// Registers a cpufreq driver with the rest of the kernel.
+    pub fn register(
+        name: &'static CStr,
+        data: T::Data,
+        flags: u16,
+        boost: bool,
+    ) -> Result<Box<Self>> {
+        let mut reg = Self::new()?;
+        let drv = reg.drv.get_mut();
+
+        // Account for the trailing null character.
+        let len = name.len() + 1;
+        if len > drv.name.len() {
+            return Err(EINVAL);
+        };
+
+        // SAFETY: `name` is a valid Cstr, and we are copying it to an array of equal or larger
+        // size.
+        let name = unsafe { &*(name.as_bytes_with_nul() as *const [u8] as *const [i8]) };
+        drv.name[..len].copy_from_slice(name);
+
+        drv.boost_enabled = boost;
+        drv.flags = flags;
+
+        // Allocate an array of 3 pointers to be passed to the C code.
+        let mut attr = Box::new([ptr::null_mut(); 3], GFP_KERNEL)?;
+        let mut next = 0;
+
+        // 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 _ };
+        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 _ };
+            next += 1;
+        }
+        attr[next] = ptr::null_mut();
+
+        // Pass the ownership of the memory block to the C code. This will be freed when
+        // the [`Registration`] object goes out of scope.
+        drv.attr = Box::leak(attr) as *mut _;
+
+        // Initialize mandatory callbacks.
+        drv.init = Some(Self::init_callback);
+        drv.verify = Some(Self::verify_callback);
+
+        // Initialize optional callbacks.
+        drv.setpolicy = if T::HAS_SETPOLICY {
+            Some(Self::setpolicy_callback)
+        } else {
+            None
+        };
+        drv.target = if T::HAS_TARGET {
+            Some(Self::target_callback)
+        } else {
+            None
+        };
+        drv.target_index = if T::HAS_TARGET_INDEX {
+            Some(Self::target_index_callback)
+        } else {
+            None
+        };
+        drv.fast_switch = if T::HAS_FAST_SWITCH {
+            Some(Self::fast_switch_callback)
+        } else {
+            None
+        };
+        drv.adjust_perf = if T::HAS_ADJUST_PERF {
+            Some(Self::adjust_perf_callback)
+        } else {
+            None
+        };
+        drv.get_intermediate = if T::HAS_GET_INTERMEDIATE {
+            Some(Self::get_intermediate_callback)
+        } else {
+            None
+        };
+        drv.target_intermediate = if T::HAS_TARGET_INTERMEDIATE {
+            Some(Self::target_intermediate_callback)
+        } else {
+            None
+        };
+        drv.get = if T::HAS_GET {
+            Some(Self::get_callback)
+        } else {
+            None
+        };
+        drv.update_limits = if T::HAS_UPDATE_LIMITS {
+            Some(Self::update_limits_callback)
+        } else {
+            None
+        };
+        drv.bios_limit = if T::HAS_BIOS_LIMIT {
+            Some(Self::bios_limit_callback)
+        } else {
+            None
+        };
+        drv.online = if T::HAS_ONLINE {
+            Some(Self::online_callback)
+        } else {
+            None
+        };
+        drv.offline = if T::HAS_OFFLINE {
+            Some(Self::offline_callback)
+        } else {
+            None
+        };
+        drv.exit = if T::HAS_EXIT {
+            Some(Self::exit_callback)
+        } else {
+            None
+        };
+        drv.suspend = if T::HAS_SUSPEND {
+            Some(Self::suspend_callback)
+        } else {
+            None
+        };
+        drv.resume = if T::HAS_RESUME {
+            Some(Self::resume_callback)
+        } else {
+            None
+        };
+        drv.ready = if T::HAS_READY {
+            Some(Self::ready_callback)
+        } else {
+            None
+        };
+        drv.set_boost = if T::HAS_SET_BOOST {
+            Some(Self::set_boost_callback)
+        } else {
+            None
+        };
+        drv.register_em = if T::HAS_REGISTER_EM {
+            Some(Self::register_em_callback)
+        } else {
+            None
+        };
+
+        // Set driver data before registering the driver, as the cpufreq core may call few
+        // callbacks before `cpufreq_register_driver()` returns.
+        reg.set_data(data)?;
+
+        // SAFETY: It is safe to register the driver with the cpufreq core in the C code.
+        to_result(unsafe { bindings::cpufreq_register_driver(reg.drv.get()) })?;
+        reg.registered = true;
+        Ok(reg)
+    }
+
+    /// Returns the previous set data for a cpufreq driver.
+    pub fn data<D: ForeignOwnable>() -> Option<<D>::Borrowed<'static>> {
+        // SAFETY: The driver data is earlier set by us from [`set_data()`].
+        let data = unsafe { bindings::cpufreq_get_driver_data() };
+        if data.is_null() {
+            None
+        } else {
+            // SAFETY: The driver data is earlier set by us from [`set_data()`].
+            Some(unsafe { D::borrow(data) })
+        }
+    }
+
+    // Sets the data for a cpufreq driver.
+    fn set_data(&mut self, data: T::Data) -> Result<()> {
+        let drv = self.drv.get_mut();
+
+        if drv.driver_data.is_null() {
+            // Pass the ownership of the data to the foreign interface.
+            drv.driver_data = <T::Data as ForeignOwnable>::into_foreign(data) as _;
+            Ok(())
+        } else {
+            Err(EBUSY)
+        }
+    }
+
+    // Clears and returns the data for a cpufreq driver.
+    fn clear_data(&mut self) -> Option<T::Data> {
+        let drv = self.drv.get_mut();
+
+        if drv.driver_data.is_null() {
+            None
+        } else {
+            // SAFETY: By the type invariants, we know that `self` owns a reference, so it is safe to
+            // relinquish it now.
+            let data = Some(unsafe { <T::Data as ForeignOwnable>::from_foreign(drv.driver_data) });
+            drv.driver_data = ptr::null_mut();
+            data
+        }
+    }
+}
+
+// cpufreq driver callbacks.
+impl<T: Driver> Registration<T> {
+    // Policy's init callback.
+    extern "C" fn init_callback(ptr: *mut bindings::cpufreq_policy) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+
+            let data = T::init(&mut policy)?;
+            policy.set_data(data)?;
+            Ok(0)
+        })
+    }
+
+    // Policy's exit callback.
+    extern "C" fn exit_callback(ptr: *mut bindings::cpufreq_policy) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+
+            let data = policy.clear_data();
+            T::exit(&mut policy, data).map(|_| 0)
+        })
+    }
+
+    // Policy's online callback.
+    extern "C" fn online_callback(ptr: *mut bindings::cpufreq_policy) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::online(&mut policy).map(|_| 0)
+        })
+    }
+
+    // Policy's offline callback.
+    extern "C" fn offline_callback(ptr: *mut bindings::cpufreq_policy) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::offline(&mut policy).map(|_| 0)
+        })
+    }
+
+    // Policy's suspend callback.
+    extern "C" fn suspend_callback(ptr: *mut bindings::cpufreq_policy) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::suspend(&mut policy).map(|_| 0)
+        })
+    }
+
+    // Policy's resume callback.
+    extern "C" fn resume_callback(ptr: *mut bindings::cpufreq_policy) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::resume(&mut policy).map(|_| 0)
+        })
+    }
+
+    // Policy's ready callback.
+    extern "C" fn ready_callback(ptr: *mut bindings::cpufreq_policy) {
+        // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+        // duration of this call, so it is guaranteed to remain alive for the lifetime of
+        // `ptr`.
+        let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+        T::ready(&mut policy);
+    }
+
+    // Policy's verify callback.
+    extern "C" fn verify_callback(ptr: *mut bindings::cpufreq_policy_data) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut data = unsafe { PolicyData::from_raw_policy_data(ptr) };
+            T::verify(&mut data).map(|_| 0)
+        })
+    }
+
+    // Policy's setpolicy callback.
+    extern "C" fn setpolicy_callback(ptr: *mut bindings::cpufreq_policy) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::setpolicy(&mut policy).map(|_| 0)
+        })
+    }
+
+    // Policy's target callback.
+    extern "C" fn target_callback(
+        ptr: *mut bindings::cpufreq_policy,
+        target_freq: u32,
+        relation: u32,
+    ) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::target(&mut policy, target_freq, Relation::new(relation)?).map(|_| 0)
+        })
+    }
+
+    // Policy's target_index callback.
+    extern "C" fn target_index_callback(
+        ptr: *mut bindings::cpufreq_policy,
+        index: u32,
+    ) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::target_index(&mut policy, index).map(|_| 0)
+        })
+    }
+
+    // Policy's fast_switch callback.
+    extern "C" fn fast_switch_callback(
+        ptr: *mut bindings::cpufreq_policy,
+        target_freq: u32,
+    ) -> core::ffi::c_uint {
+        // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+        // duration of this call, so it is guaranteed to remain alive for the lifetime of
+        // `ptr`.
+        let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+        T::fast_switch(&mut policy, target_freq)
+    }
+
+    // Policy's adjust_perf callback.
+    extern "C" fn adjust_perf_callback(cpu: u32, min_perf: u64, target_perf: u64, capacity: u64) {
+        if let Ok(mut policy) = Policy::from_cpu(cpu) {
+            T::adjust_perf(&mut policy, min_perf, target_perf, capacity);
+        }
+    }
+
+    // Policy's get_intermediate callback.
+    extern "C" fn get_intermediate_callback(
+        ptr: *mut bindings::cpufreq_policy,
+        index: u32,
+    ) -> core::ffi::c_uint {
+        // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+        // duration of this call, so it is guaranteed to remain alive for the lifetime of
+        // `ptr`.
+        let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+        T::get_intermediate(&mut policy, index)
+    }
+
+    // Policy's target_intermediate callback.
+    extern "C" fn target_intermediate_callback(
+        ptr: *mut bindings::cpufreq_policy,
+        index: u32,
+    ) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::target_intermediate(&mut policy, index).map(|_| 0)
+        })
+    }
+
+    // Policy's get callback.
+    extern "C" fn get_callback(cpu: u32) -> core::ffi::c_uint {
+        // SAFETY: Get the policy for a CPU.
+        Policy::from_cpu(cpu).map_or(0, |mut policy| T::get(&mut policy).map_or(0, |f| f))
+    }
+
+    // Policy's update_limit callback.
+    extern "C" fn update_limits_callback(cpu: u32) {
+        // SAFETY: Get the policy for a CPU.
+        if let Ok(mut policy) = Policy::from_cpu(cpu) {
+            T::update_limits(&mut policy);
+        }
+    }
+
+    // Policy's bios_limit callback.
+    extern "C" fn bios_limit_callback(cpu: i32, limit: *mut u32) -> core::ffi::c_int {
+        from_result(|| {
+            let mut policy = Policy::from_cpu(cpu as u32)?;
+
+            // SAFETY: The pointer is guaranteed by the C code to be valid.
+            T::bios_limit(&mut policy, &mut (unsafe { *limit })).map(|_| 0)
+        })
+    }
+
+    // Policy's set_boost callback.
+    extern "C" fn set_boost_callback(
+        ptr: *mut bindings::cpufreq_policy,
+        state: i32,
+    ) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+            // duration of this call, so it is guaranteed to remain alive for the lifetime of
+            // `ptr`.
+            let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+            T::set_boost(&mut policy, state).map(|_| 0)
+        })
+    }
+
+    // Policy's register_em callback.
+    extern "C" fn register_em_callback(ptr: *mut bindings::cpufreq_policy) {
+        // SAFETY: `ptr` is valid by the contract with the C code. `policy` is alive only for the
+        // duration of this call, so it is guaranteed to remain alive for the lifetime of
+        // `ptr`.
+        let mut policy = unsafe { Policy::from_raw_policy(ptr) };
+        T::register_em(&mut policy);
+    }
+}
+
+impl<T: Driver> Drop for Registration<T> {
+    // Removes the registration from the kernel if it has completed successfully before.
+    fn drop(&mut self) {
+        pr_info!("Registration dropped\n");
+        let drv = self.drv.get_mut();
+
+        if self.registered {
+            // SAFETY: The driver was earlier registered from `register()`.
+            unsafe { bindings::cpufreq_unregister_driver(drv) };
+        }
+
+        // Free the previously leaked memory to the C code.
+        if !drv.attr.is_null() {
+            // SAFETY: The pointer was earlier initialized from the result of `Box::leak`.
+            unsafe { drop(Box::from_raw(drv.attr)) };
+        }
+
+        // Free data
+        drop(self.clear_data());
+    }
+}
-- 
2.31.1.272.g89b43f80a514