| Message ID | 854f7b8c9cbcc7f38fe5ed548290f41224478b40.1736766672.git.viresh.kumar@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | Rust bindings for cpufreq and OPP core + sample driver | expand |
On Wed, Jan 15, 2025 at 01:28:59PM +0530, Viresh Kumar wrote: > On 15-01-25, 08:54, Greg KH wrote: > > Ah, but that's not really something that SAFETY should override, right? > > > > Yes, you know your implementation of this will stop using the pointer in > > the hotplug callback before it goes away but that's not documented here. > > And having the device "fail" afterward isn't really ok either as you are > > relying on the driver core to always check for this and I'm not so sure > > that it always does on all codepaths. > > > > But, I'm ok with this for now, as you are just copying the bad C model > > at the moment, but it really feels like a huge foot-gun waiting to go > > off. Any way to put some more documentation here as in "use this at > > your own risk!"? > > What about marking it unsafe ? That would require callers to document > why it is safe to call this. And yes add more documentation here too. Sure, that's fine with me.
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index e9fdceb568b8..d63e7f6d10ea 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -10,6 +10,7 @@ #include <linux/blk-mq.h> #include <linux/blk_types.h> #include <linux/blkdev.h> +#include <linux/cpu.h> #include <linux/cred.h> #include <linux/errname.h> #include <linux/ethtool.h> diff --git a/rust/kernel/cpu.rs b/rust/kernel/cpu.rs new file mode 100644 index 000000000000..422e874627d2 --- /dev/null +++ b/rust/kernel/cpu.rs @@ -0,0 +1,26 @@ +// 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. +pub fn from_cpu(cpu: u32) -> Result<&'static Device> { + // 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. + 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 2d5c3d7d2e21..e9106b29c359 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -39,6 +39,7 @@ pub mod block; #[doc(hidden)] pub mod build_assert; +pub mod cpu; pub mod cred; pub mod device; pub mod device_id;
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> --- rust/bindings/bindings_helper.h | 1 + rust/kernel/cpu.rs | 26 ++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 3 files changed, 28 insertions(+) create mode 100644 rust/kernel/cpu.rs