Date: Fri, 07 Jun 2024 13:38:17 +0300
From: Manos Pitsidianakis <manos.pitsidianakis@...aro.org>
To: Viresh Kumar <viresh.kumar@...aro.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, Bjö rn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>, Alice Ryhl <aliceryhl@...gle.com>
Cc: Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org, Vincent Guittot <vincent.guittot@...aro.org>, Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>, rust-for-linux@...r.kernel.org, Manos Pitsidianakis <manos.pitsidianakis@...aro.org>, Erik Schilling <erik.schilling@...aro.org>, Alex Benné e <alex.bennee@...aro.org>, Joakim Bech <joakim.bech@...aro.org>, Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH V2 2/8] rust: Extend OPP bindings for the OPP table

On Fri, 07 Jun 2024 12:12, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>This extends OPP bindings with the bindings for the `struct opp_table`.
>
>Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>---
> rust/kernel/opp.rs | 374 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 372 insertions(+), 2 deletions(-)
>
>diff --git a/rust/kernel/opp.rs b/rust/kernel/opp.rs
>index 9e5cf0412ed5..06f36845047f 100644
>--- a/rust/kernel/opp.rs
>+++ b/rust/kernel/opp.rs
>@@ -7,9 +7,9 @@
> //! C header: [`include/linux/pm_opp.h`](../../../../../../include/linux/pm_opp.h)
> 
> use crate::{
>-    bindings,
>+    bindings, cpumask,
>     device::Device,
>-    error::{code::*, to_result, Result},
>+    error::{code::*, from_err_ptr, to_result, Error, Result},
>     types::{ARef, AlwaysRefCounted, Opaque},
> };
> 
>@@ -31,6 +31,376 @@ pub fn new(freq: u64, u_volt: u64, level: u32, turbo: bool) -> Self {
>     }
> }
> 
>+/// OPP search types.
>+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
>+pub enum SearchType {
>+    /// Search for exact value.
>+    Exact,
>+    /// Search for highest value less than equal to value.
>+    Floor,
>+    /// Search for lowest value greater than equal to value.
>+    Ceil,
>+}

Seeing this enum made me think about memory layouts which are not stable 
in Rust and can change between compilations unless they have a specific 
`repr`.

Not related to this series directly, has there been discussion about 
guaranteeing struct layouts in kernel APIs? It'd require a lot of things 
to happen to cause a problem (multiple users of an API in the kernel in 
separate compilation units maybe even compiled with different rustc 
versions).

>+
>+/// Operating performance point (OPP) table.
>+///
>+/// # Invariants
>+///
>+/// The pointer stored in `Self` is non-null and valid for the lifetime of the ARef instance. In
>+/// particular, the ARef instance owns an increment on underlying object’s reference count.
>+pub struct Table {
>+    ptr: *mut bindings::opp_table,
>+    dev: ARef<Device>,
>+    em: bool,
>+    of: bool,
>+    cpumask: Option<cpumask::Cpumask>,
>+}
>+
>+// SAFETY: The fields of `Table` are safe to be used from any thread.
>+unsafe impl Send for Table {}
>+
>+// SAFETY: The fields of `Table` are safe to be referenced from any thread.
>+unsafe impl Sync for Table {}
>+
>+impl Table {
>+    /// Creates a new OPP table instance from raw pointer.
>+    ///
>+    /// # Safety
>+    ///
>+    /// Callers must ensure that `ptr` is valid and non-null.
>+    unsafe fn from_ptr(ptr: *mut bindings::opp_table, dev: ARef<Device>) -> Self {
>+        // SAFETY: By the safety requirements, ptr is valid and its refcount will be incremented.
>+        unsafe { bindings::dev_pm_opp_get_opp_table_ref(ptr) };
>+
>+        Self {
>+            ptr,
>+            dev,
>+            em: false,
>+            of: false,
>+            cpumask: None,
>+        }
>+    }
>+
>+    /// Find OPP table from device.
>+    pub fn from_dev(dev: ARef<Device>) -> Result<Self> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements. Refcount of the OPP table is incremented as well.
>+        let ptr = from_err_ptr(unsafe { bindings::dev_pm_opp_get_opp_table(dev.as_raw()) })?;
>+
>+        Ok(Self {
>+            ptr,
>+            dev: dev.clone(),

Clone is not probably not needed here, right? the argument value will be 
dropped after this.

>+            em: false,
>+            of: false,
>+            cpumask: None,
>+        })
>+    }
>+
>+    /// Add device tree based OPP table for the device.
>+    #[cfg(CONFIG_OF)]
>+    pub fn from_of(dev: ARef<Device>, index: i32) -> Result<Self> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements. Refcount of the OPP table is incremented as well.
>+        to_result(unsafe { bindings::dev_pm_opp_of_add_table_indexed(dev.as_raw(), index) })?;
>+
>+        // Fetch the newly created table.
>+        let mut table = Self::from_dev(dev)?;
>+        table.of = true;
>+
>+        Ok(table)
>+    }
>+
>+    // Remove device tree based OPP table for the device.
>+    #[cfg(CONFIG_OF)]
>+    fn remove_of(&self) {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements. We took the reference from `from_of` earlier, it is safe to drop the same
>+        // now.
>+        unsafe { bindings::dev_pm_opp_of_remove_table(self.dev.as_raw()) };
>+    }
>+
>+    /// Add device tree based OPP table for CPU devices.
>+    #[cfg(CONFIG_OF)]
>+    pub fn from_of_cpumask(dev: ARef<Device>, cpumask: &mut cpumask::Cpumask) -> Result<Self> {
>+        // SAFETY: The cpumask is valid and the returned ptr will be owned by the [`Table`] instance.
>+        to_result(unsafe { bindings::dev_pm_opp_of_cpumask_add_table(cpumask.as_ptr()) })?;
>+
>+        // Fetch the newly created table.
>+        let mut table = Self::from_dev(dev)?;
>+        // SAFETY: The `cpumask` is guaranteed by the C code to be valid.
>+        table.cpumask = Some(unsafe { cpumask::Cpumask::new(cpumask.as_mut_ptr()) });
>+
>+        Ok(table)
>+    }
>+
>+    // Remove device tree based OPP table for CPU devices.
>+    #[cfg(CONFIG_OF)]
>+    fn remove_of_cpumask(&self, cpumask: &cpumask::Cpumask) {
>+        // SAFETY: The cpumask is valid and we took the reference from `from_of_cpumask` earlier,
>+        // it is safe to drop the same now.
>+        unsafe { bindings::dev_pm_opp_of_cpumask_remove_table(cpumask.as_ptr()) };
>+    }
>+
>+    /// Returns the number of OPPs in the table.
>+    pub fn opp_count(&self) -> Result<u32> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        let ret = unsafe { bindings::dev_pm_opp_get_opp_count(self.dev.as_raw()) };
>+        if ret < 0 {
>+            Err(Error::from_errno(ret))
>+        } else {
>+            Ok(ret as u32)
>+        }
>+    }
>+
>+    /// Returns max clock latency of the OPPs in the table.
>+    pub fn max_clock_latency(&self) -> u64 {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        unsafe { bindings::dev_pm_opp_get_max_clock_latency(self.dev.as_raw()) }
>+    }
>+
>+    /// Returns max volt latency of the OPPs in the table.
>+    pub fn max_volt_latency(&self) -> u64 {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        unsafe { bindings::dev_pm_opp_get_max_volt_latency(self.dev.as_raw()) }
>+    }
>+
>+    /// Returns max transition latency of the OPPs in the table.
>+    pub fn max_transition_latency(&self) -> u64 {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        unsafe { bindings::dev_pm_opp_get_max_transition_latency(self.dev.as_raw()) }
>+    }
>+
>+    /// Returns the suspend OPP.
>+    pub fn suspend_freq(&self) -> u64 {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        unsafe { bindings::dev_pm_opp_get_suspend_opp_freq(self.dev.as_raw()) }
>+    }
>+
>+    /// Synchronizes regulators used by the OPP table.
>+    pub fn sync_regulators(&self) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe { bindings::dev_pm_opp_sync_regulators(self.dev.as_raw()) })
>+    }
>+
>+    /// Gets sharing CPUs.
>+    pub fn sharing_cpus(dev: ARef<Device>, cpumask: &mut cpumask::Cpumask) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe {
>+            bindings::dev_pm_opp_get_sharing_cpus(dev.as_raw(), cpumask.as_mut_ptr())
>+        })
>+    }
>+
>+    /// Sets sharing CPUs.
>+    pub fn set_sharing_cpus(&self, cpumask: &cpumask::Cpumask) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe {
>+            bindings::dev_pm_opp_set_sharing_cpus(self.dev.as_raw(), cpumask.as_ptr())
>+        })
>+    }
>+
>+    /// Gets sharing CPUs from Device tree.
>+    #[cfg(CONFIG_OF)]
>+    pub fn of_sharing_cpus(dev: ARef<Device>, cpumask: &mut cpumask::Cpumask) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe {
>+            bindings::dev_pm_opp_of_get_sharing_cpus(dev.as_raw(), cpumask.as_mut_ptr())
>+        })
>+    }
>+
>+    /// Updates the voltage value for an OPP.
>+    pub fn adjust_voltage(
>+        &self,
>+        freq: u64,
>+        u_volt: u64,
>+        u_volt_min: u64,
>+        u_volt_max: u64,
>+    ) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe {
>+            bindings::dev_pm_opp_adjust_voltage(
>+                self.dev.as_raw(),
>+                freq,
>+                u_volt,
>+                u_volt_min,
>+                u_volt_max,
>+            )
>+        })
>+    }
>+
>+    /// Sets a matching OPP based on frequency.
>+    pub fn set_rate(&self, freq: u64) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe { bindings::dev_pm_opp_set_rate(self.dev.as_raw(), freq) })
>+    }
>+
>+    /// Sets exact OPP.
>+    pub fn set_opp(&self, opp: ARef<OPP>) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe { bindings::dev_pm_opp_set_opp(self.dev.as_raw(), opp.as_mut_ptr()) })
>+    }
>+
>+    /// Finds OPP based on frequency.
>+    pub fn opp_from_freq(
>+        &self,
>+        mut freq: u64,
>+        available: Option<bool>,
>+        index: Option<u32>,
>+        stype: SearchType,
>+    ) -> Result<ARef<OPP>> {
>+        let rdev = self.dev.as_raw();
>+        let index = index.unwrap_or(0);
>+
>+        let ptr = from_err_ptr(match stype {
>+            SearchType::Exact => {
>+                if let Some(available) = available {
>+                    // SAFETY: The requirements are satisfied by the existence of `Device` and
>+                    // its safety requirements. The returned ptr will be owned by the new [`OPP`]
>+                    // instance.
>+                    unsafe {
>+                        bindings::dev_pm_opp_find_freq_exact_indexed(rdev, freq, index, available)
>+                    }
>+                } else {
>+                    return Err(EINVAL);
>+                }
>+            }
>+
>+            // SAFETY: The requirements are satisfied by the existence of `Device` and its
>+            // safety requirements. The returned ptr will be owned by the new [`OPP`] instance.
>+            SearchType::Ceil => unsafe {
>+                bindings::dev_pm_opp_find_freq_ceil_indexed(rdev, &mut freq as *mut u64, index)
>+            },
>+
>+            // SAFETY: The requirements are satisfied by the existence of `Device` and its
>+            // safety requirements. The returned ptr will be owned by the new [`OPP`] instance.
>+            SearchType::Floor => unsafe {
>+                bindings::dev_pm_opp_find_freq_floor_indexed(rdev, &mut freq as *mut u64, index)
>+            },
>+        })?;
>+
>+        // SAFETY: The `ptr` is guaranteed by the C code to be valid.
>+        unsafe { OPP::from_ptr_owned(ptr) }
>+    }
>+
>+    /// Finds OPP based on level.
>+    pub fn opp_from_level(&self, mut level: u32, stype: SearchType) -> Result<ARef<OPP>> {
>+        let rdev = self.dev.as_raw();
>+
>+        let ptr = from_err_ptr(match stype {
>+            // SAFETY: The requirements are satisfied by the existence of `Device` and its
>+            // safety requirements. The returned ptr will be owned by the new [`OPP`] instance.
>+            SearchType::Exact => unsafe { bindings::dev_pm_opp_find_level_exact(rdev, level) },
>+

Minor style comment, the empty lines between match patterns are unusual

>+            // SAFETY: The requirements are satisfied by the existence of `Device` and its
>+            // safety requirements. The returned ptr will be owned by the new [`OPP`] instance.
>+            SearchType::Ceil => unsafe {
>+                bindings::dev_pm_opp_find_level_ceil(rdev, &mut level as *mut u32)
>+            },
>+
>+            // SAFETY: The requirements are satisfied by the existence of `Device` and its
>+            // safety requirements. The returned ptr will be owned by the new [`OPP`] instance.
>+            SearchType::Floor => unsafe {
>+                bindings::dev_pm_opp_find_level_floor(rdev, &mut level as *mut u32)
>+            },
>+        })?;
>+
>+        // SAFETY: The `ptr` is guaranteed by the C code to be valid.
>+        unsafe { OPP::from_ptr_owned(ptr) }
>+    }
>+
>+    /// Finds OPP based on bandwidth.
>+    pub fn opp_from_bw(&self, mut bw: u32, index: i32, stype: SearchType) -> Result<ARef<OPP>> {
>+        let rdev = self.dev.as_raw();
>+
>+        let ptr = from_err_ptr(match stype {
>+            // The OPP core doesn't support this yet.
>+            SearchType::Exact => return Err(EINVAL),
>+
>+            // SAFETY: The requirements are satisfied by the existence of `Device` and its
>+            // safety requirements. The returned ptr will be owned by the new [`OPP`] instance.
>+            SearchType::Ceil => unsafe {
>+                bindings::dev_pm_opp_find_bw_ceil(rdev, &mut bw as *mut u32, index)
>+            },
>+
>+            // SAFETY: The requirements are satisfied by the existence of `Device` and its
>+            // safety requirements. The returned ptr will be owned by the new [`OPP`] instance.
>+            SearchType::Floor => unsafe {
>+                bindings::dev_pm_opp_find_bw_floor(rdev, &mut bw as *mut u32, index)
>+            },
>+        })?;
>+
>+        // SAFETY: The `ptr` is guaranteed by the C code to be valid.
>+        unsafe { OPP::from_ptr_owned(ptr) }
>+    }
>+
>+    /// Enable the OPP.
>+    pub fn enable_opp(&self, freq: u64) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe { bindings::dev_pm_opp_enable(self.dev.as_raw(), freq) })
>+    }
>+
>+    /// Disable the OPP.
>+    pub fn disable_opp(&self, freq: u64) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe { bindings::dev_pm_opp_disable(self.dev.as_raw(), freq) })
>+    }
>+
>+    /// Registers with Energy model.
>+    #[cfg(CONFIG_OF)]
>+    pub fn of_register_em(&mut self, cpumask: &mut cpumask::Cpumask) -> Result<()> {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements.
>+        to_result(unsafe {
>+            bindings::dev_pm_opp_of_register_em(self.dev.as_raw(), cpumask.as_mut_ptr())
>+        })?;
>+
>+        self.em = true;
>+        Ok(())
>+    }
>+
>+    // Unregisters with Energy model.
>+    #[cfg(CONFIG_OF)]
>+    fn of_unregister_em(&self) {
>+        // SAFETY: The requirements are satisfied by the existence of `Device` and its safety
>+        // requirements. We registered with the EM framework earlier, it is safe to unregister now.
>+        unsafe { bindings::em_dev_unregister_perf_domain(self.dev.as_raw()) };
>+    }
>+}
>+
>+impl Drop for Table {
>+    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_put_opp_table(self.ptr) };
>+
>+        #[cfg(CONFIG_OF)]
>+        {
>+            if self.em {
>+                self.of_unregister_em();
>+            }
>+
>+            if self.of {
>+                self.remove_of();
>+            } else if let Some(cpumask) = &self.cpumask {
>+                self.remove_of_cpumask(cpumask);
>+            }
>+        }
>+    }
>+}
>+
> /// Operating performance point (OPP).
> ///
> /// # Invariants
>-- 
>2.31.1.272.g89b43f80a514
>

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