[RFC,V2,3/8] rust: Extend OPP bindings for the configuration options

diff --git a/rust/kernel/opp.rs b/rust/kernel/opp.rs
index 06f36845047f..ebcb77b52558 100644
--- a/rust/kernel/opp.rs
+++ b/rust/kernel/opp.rs
@@ -9,11 +9,28 @@ 
 use crate::{
     bindings, cpumask,
     device::Device,
-    error::{code::*, from_err_ptr, to_result, Error, Result},
+    error::{code::*, from_err_ptr, from_result, to_result, Error, Result, VTABLE_DEFAULT_ERROR},
+    prelude::*,
+    str::CString,
     types::{ARef, AlwaysRefCounted, Opaque},
 };
 
-use core::ptr;
+use core::{ffi::c_char, marker::PhantomData, ptr};
+
+use macros::vtable;
+
+// Creates a null-terminated slice of pointers to Cstrings.
+fn to_c_str_array(names: &Vec<CString>) -> Result<Vec<*const c_char>> {
+    // Allocated a null-terminated vector of pointers.
+    let mut list = Vec::with_capacity(names.len() + 1, GFP_KERNEL)?;
+
+    for name in names.iter() {
+        list.push(name.as_ptr() as _, GFP_KERNEL)?;
+    }
+
+    list.push(ptr::null(), GFP_KERNEL)?;
+    Ok(list)
+}
 
 /// Equivalent to `struct dev_pm_opp_data` in the C Code.
 #[repr(transparent)]
@@ -42,6 +59,290 @@  pub enum SearchType {
     Ceil,
 }
 
+/// Implement this trait to provide OPP Configuration callbacks.
+#[vtable]
+pub trait ConfigOps {
+    /// Called by the OPP core to configure OPP clks.
+    fn config_clks(
+        _dev: ARef<Device>,
+        _table: &Table,
+        _opp: ARef<OPP>,
+        _scaling_down: bool,
+    ) -> Result<()> {
+        kernel::build_error(VTABLE_DEFAULT_ERROR)
+    }
+
+    /// Called by the OPP core to configure OPP regulators.
+    fn config_regulators(
+        _dev: ARef<Device>,
+        _opp_old: ARef<OPP>,
+        _opp_new: ARef<OPP>,
+        _data: *mut *mut bindings::regulator,
+        _count: u32,
+    ) -> Result<()> {
+        kernel::build_error(VTABLE_DEFAULT_ERROR)
+    }
+}
+
+/// Config token returned by the C code.
+pub struct ConfigToken(i32);
+
+impl Drop for ConfigToken {
+    fn drop(&mut self) {
+        // SAFETY: By the type invariants, we know that `self` owns a reference, so it is safe
+        // to relinquish it now.
+        unsafe { bindings::dev_pm_opp_clear_config(self.0) };
+    }
+}
+
+/// Equivalent to `struct dev_pm_opp_config` in the C Code.
+pub struct Config<T: ConfigOps> {
+    clk_names: Option<Vec<CString>>,
+    prop_name: Option<CString>,
+    regulator_names: Option<Vec<CString>>,
+    genpd_names: Option<Vec<CString>>,
+    supported_hw: Option<Vec<u32>>,
+    required_devs: Option<Vec<ARef<Device>>>,
+    _data: PhantomData<T>,
+}
+
+impl<T: ConfigOps> Config<T> {
+    /// Creates a new instance of [`Config`].
+    pub fn new() -> Self {
+        Self {
+            clk_names: None,
+            prop_name: None,
+            regulator_names: None,
+            genpd_names: None,
+            supported_hw: None,
+            required_devs: None,
+            _data: PhantomData,
+        }
+    }
+
+    /// Initializes clock names.
+    pub fn set_clk_names(mut self, names: Vec<CString>) -> Result<Self> {
+        // Already configured.
+        if self.clk_names.is_some() {
+            return Err(EBUSY);
+        }
+
+        if names.is_empty() {
+            return Err(EINVAL);
+        }
+
+        self.clk_names = Some(names);
+        Ok(self)
+    }
+
+    /// Initializes property name.
+    pub fn set_prop_name(mut self, name: CString) -> Result<Self> {
+        // Already configured.
+        if self.prop_name.is_some() {
+            return Err(EBUSY);
+        }
+
+        self.prop_name = Some(name);
+        Ok(self)
+    }
+
+    /// Initializes regulator names.
+    pub fn set_regulator_names(mut self, names: Vec<CString>) -> Result<Self> {
+        // Already configured.
+        if self.regulator_names.is_some() {
+            return Err(EBUSY);
+        }
+
+        if names.is_empty() {
+            return Err(EINVAL);
+        }
+
+        self.regulator_names = Some(names);
+
+        Ok(self)
+    }
+
+    /// Initializes genpd names.
+    pub fn set_genpd_names(mut self, names: Vec<CString>) -> Result<Self> {
+        // Already configured. Only one of genpd or required devs can be configured.
+        if self.genpd_names.is_some() || self.required_devs.is_some() {
+            return Err(EBUSY);
+        }
+
+        if names.is_empty() {
+            return Err(EINVAL);
+        }
+
+        self.genpd_names = Some(names);
+        Ok(self)
+    }
+
+    /// Initializes required devices.
+    pub fn set_required_devs(mut self, devs: Vec<ARef<Device>>) -> Result<Self> {
+        // Already configured. Only one of genpd or required devs can be configured.
+        if self.genpd_names.is_some() || self.required_devs.is_some() {
+            return Err(EBUSY);
+        }
+
+        if devs.is_empty() {
+            return Err(EINVAL);
+        }
+
+        self.required_devs = Some(devs);
+        Ok(self)
+    }
+
+    /// Initializes supported hardware.
+    pub fn set_supported_hw(mut self, hw: Vec<u32>) -> Result<Self> {
+        // Already configured.
+        if self.supported_hw.is_some() {
+            return Err(EBUSY);
+        }
+
+        if hw.is_empty() {
+            return Err(EINVAL);
+        }
+
+        self.supported_hw = Some(hw);
+        Ok(self)
+    }
+
+    /// Sets the configuration with the OPP core.
+    pub fn set(self, dev: ARef<Device>) -> Result<ConfigToken> {
+        let (_clk_list, clk_names) = match &self.clk_names {
+            Some(x) => {
+                let list = to_c_str_array(x)?;
+                let ptr = list.as_ptr();
+                (Some(list), ptr)
+            }
+            None => (None, ptr::null()),
+        };
+
+        let (_regulator_list, regulator_names) = match &self.regulator_names {
+            Some(x) => {
+                let list = to_c_str_array(x)?;
+                let ptr = list.as_ptr();
+                (Some(list), ptr)
+            }
+            None => (None, ptr::null()),
+        };
+
+        let (_genpd_list, genpd_names) = match &self.genpd_names {
+            Some(x) => {
+                let list = to_c_str_array(x)?;
+                let ptr = list.as_ptr();
+                (Some(list), ptr)
+            }
+            None => (None, ptr::null()),
+        };
+
+        let prop_name = match &self.prop_name {
+            Some(x) => x.as_char_ptr(),
+            None => ptr::null(),
+        };
+
+        let (supported_hw, supported_hw_count) = match &self.supported_hw {
+            Some(x) => (x.as_ptr(), x.len() as u32),
+            None => (ptr::null(), 0),
+        };
+
+        let (_required_devs_list, required_devs) = match &self.required_devs {
+            Some(x) => {
+                // Create a non-NULL-terminated vectorof pointers.
+                let mut list = Vec::with_capacity(x.len(), GFP_KERNEL)?;
+
+                for dev in x.iter() {
+                    list.push(dev.as_raw(), GFP_KERNEL)?;
+                }
+
+                let ptr = list.as_mut_ptr();
+                (Some(list), ptr)
+            }
+            None => (None, ptr::null_mut()),
+        };
+
+        let mut config = bindings::dev_pm_opp_config {
+            clk_names,
+            config_clks: if T::HAS_CONFIG_CLKS {
+                Some(Self::config_clks)
+            } else {
+                None
+            },
+            prop_name,
+            regulator_names,
+            config_regulators: if T::HAS_CONFIG_REGULATORS {
+                Some(Self::config_regulators)
+            } else {
+                None
+            },
+            genpd_names,
+            supported_hw,
+            supported_hw_count,
+
+            // Don't need to support virt_devs for now.
+            virt_devs: ptr::null_mut(),
+            required_devs,
+        };
+
+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
+        // requirements. The OPP core guarantees to not use fields of `config`, after this call has
+        // returned and so we don't need to save a copy of them for future use
+        let ret = unsafe { bindings::dev_pm_opp_set_config(dev.as_raw(), &mut config) };
+        if ret < 0 {
+            Err(Error::from_errno(ret))
+        } else {
+            Ok(ConfigToken(ret))
+        }
+    }
+
+    // Config's config_clks callback.
+    extern "C" fn config_clks(
+        dev: *mut bindings::device,
+        opp_table: *mut bindings::opp_table,
+        opp: *mut bindings::dev_pm_opp,
+        _data: *mut core::ffi::c_void,
+        scaling_down: bool,
+    ) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: 'dev' is guaranteed by the C code to be valid.
+            let dev = unsafe { Device::from_raw(dev) };
+            T::config_clks(
+                dev.clone(),
+                // SAFETY: 'opp_table' is guaranteed by the C code to be valid.
+                &unsafe { Table::from_ptr(opp_table, dev) },
+                // SAFETY: 'opp' is guaranteed by the C code to be valid.
+                unsafe { OPP::from_ptr(opp)? },
+                scaling_down,
+            )
+            .map(|_| 0)
+        })
+    }
+
+    // Config's config_regulators callback.
+    extern "C" fn config_regulators(
+        dev: *mut bindings::device,
+        old_opp: *mut bindings::dev_pm_opp,
+        new_opp: *mut bindings::dev_pm_opp,
+        regulators: *mut *mut bindings::regulator,
+        count: core::ffi::c_uint,
+    ) -> core::ffi::c_int {
+        from_result(|| {
+            // SAFETY: 'dev' is guaranteed by the C code to be valid.
+            let dev = unsafe { Device::from_raw(dev) };
+            T::config_regulators(
+                dev,
+                // SAFETY: 'old_opp' is guaranteed by the C code to be valid.
+                unsafe { OPP::from_ptr(old_opp)? },
+                // SAFETY: 'new_opp' is guaranteed by the C code to be valid.
+                unsafe { OPP::from_ptr(new_opp)? },
+                regulators,
+                count,
+            )
+            .map(|_| 0)
+        })
+    }
+}
+
 /// Operating performance point (OPP) table.
 ///
 /// # Invariants