rust: opp: Extend OPP abstractions with cpufreq support

Extend the OPP abstractions to include support for interacting with the
cpufreq core, including the ability to retrieve frequency tables from
OPP table.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Author: vireshk

rust/kernel/opp.rs

@@ -19,6 +19,69 @@ use crate::{
     types::{ARef, AlwaysRefCounted, Opaque},
 };
 
+#[cfg(CONFIG_CPU_FREQ)]
+/// Frequency table implementation.
+mod freq {
+    use super::*;
+    use crate::cpufreq;
+    use core::ops::Deref;
+
+    /// OPP frequency table.
+    ///
+    /// A [`cpufreq::Table`] created from [`Table`].
+    pub struct FreqTable {
+        dev: ARef<Device>,
+        ptr: *mut bindings::cpufreq_frequency_table,
+    }
+
+    impl FreqTable {
+        /// Creates a new instance of [`FreqTable`] from [`Table`].
+        pub(crate) fn new(table: &Table) -> Result<Self> {
+            let mut ptr: *mut bindings::cpufreq_frequency_table = ptr::null_mut();
+
+            // SAFETY: The requirements are satisfied by the existence of [`Device`] and its safety
+            // requirements.
+            to_result(unsafe {
+                bindings::dev_pm_opp_init_cpufreq_table(table.dev.as_raw(), &mut ptr)
+            })?;
+
+            Ok(Self {
+                dev: table.dev.clone(),
+                ptr,
+            })
+        }
+
+        /// Returns a reference to the underlying [`cpufreq::Table`].
+        #[inline]
+        fn table(&self) -> &cpufreq::Table {
+            // SAFETY: The `ptr` is guaranteed by the C code to be valid.
+            unsafe { cpufreq::Table::from_raw(self.ptr) }
+        }
+    }
+
+    impl Deref for FreqTable {
+        type Target = cpufreq::Table;
+
+        #[inline]
+        fn deref(&self) -> &Self::Target {
+            self.table()
+        }
+    }
+
+    impl Drop for FreqTable {
+        fn drop(&mut self) {
+            // SAFETY: The pointer was created via `dev_pm_opp_init_cpufreq_table`, and is only
+            // freed here.
+            unsafe {
+                bindings::dev_pm_opp_free_cpufreq_table(self.dev.as_raw(), &mut self.as_raw())
+            };
+        }
+    }
+}
+
+#[cfg(CONFIG_CPU_FREQ)]
+pub use freq::FreqTable;
+
 use core::{marker::PhantomData, ptr};
 
 use macros::vtable;
@@ -753,6 +816,13 @@ impl Table {
         })
     }
 
+    /// Creates [`FreqTable`] from [`Table`].
+    #[cfg(CONFIG_CPU_FREQ)]
+    #[inline]
+    pub fn cpufreq_table(&mut self) -> Result<FreqTable> {
+        FreqTable::new(self)
+    }
+
     /// Configures device with [`OPP`] matching the frequency value.
     #[inline]
     pub fn set_rate(&self, freq: Hertz) -> Result {