rust: cpu: Add from_cpu()

This implements cpu::from_cpu(), which returns a reference to
Device for a CPU. The C struct is created at initialization time for
CPUs and is never freed and so ARef isn't returned from this function.

The new helper will be used by Rust based cpufreq drivers.

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

diff --git a/MAINTAINERS b/MAINTAINERS
index 12cde55579a0c9e6eeaff45b1919e14331395ba8..475abf72869c02e3738dea26cc49c2359281fcab 100644 (file)
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6155,6 +6155,7 @@ F:        include/linux/cpuhotplug.h
 F:     include/linux/smpboot.h
 F:     kernel/cpu.c
 F:     kernel/smpboot.*
+F:     rust/kernel/cpu.rs
 
 CPU IDLE TIME MANAGEMENT FRAMEWORK
 M:     "Rafael J. Wysocki" <rafael@kernel.org>

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index f53d6e1a21f24070fa528631842f3b9e1171e42d..ac92c67d2c3805108588984ae04f0c4c5b371268 100644 (file)
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -11,6 +11,7 @@
 #include <linux/blk_types.h>
 #include <linux/blkdev.h>
 #include <linux/clk.h>
+#include <linux/cpu.h>
 #include <linux/cpumask.h>
 #include <linux/cred.h>
 #include <linux/device/faux.h>

diff --git a/rust/kernel/cpu.rs b/rust/kernel/cpu.rs
new file mode 100644 (file)
index 0000000..10c5c3b
--- /dev/null
+++ b/rust/kernel/cpu.rs
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generic CPU definitions.
+//!
+//! C header: [`include/linux/cpu.h`](srctree/include/linux/cpu.h)
+
+use crate::{bindings, device::Device, error::Result, prelude::ENODEV};
+
+/// Creates a new instance of CPU's device.
+///
+/// # Safety
+///
+/// Reference counting is not implemented for the CPU device in the C code. When a CPU is
+/// hot-unplugged, the corresponding CPU device is unregistered, but its associated memory
+/// is not freed.
+///
+/// Callers must ensure that the CPU device is not used after it has been unregistered.
+/// This can be achieved, for example, by registering a CPU hotplug notifier and removing
+/// any references to the CPU device within the notifier's callback.
+pub unsafe fn from_cpu(cpu: u32) -> Result<&'static Device> {
+    // SAFETY: It is safe to call `get_cpu_device()` for any CPU.
+    let ptr = unsafe { bindings::get_cpu_device(cpu) };
+    if ptr.is_null() {
+        return Err(ENODEV);
+    }
+
+    // SAFETY: The pointer returned by `get_cpu_device()`, if not `NULL`, is a valid pointer to
+    // a `struct device` and is never freed by the C code.
+    Ok(unsafe { Device::as_ref(ptr) })
+}

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 3fd7c17cbc0656f363184234521c2fe2106e95e3..de0a840fcc999d5e1324e02ebc4faf2daec5c585 100644 (file)
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -43,6 +43,7 @@ pub mod block;
 #[doc(hidden)]
 pub mod build_assert;
 pub mod clk;
+pub mod cpu;
 pub mod cpumask;
 pub mod cred;
 pub mod device;