projects/linux·blob v6.14-rc2 · refs

201 lines · 6.6 KiB

1// SPDX-License-Identifier: GPL-2.0
2
3//! Devres abstraction
4//!
5//! [`Devres`] represents an abstraction for the kernel devres (device resource management)
6//! implementation.
7
8use crate::{
9 alloc::Flags,
10 bindings,
11 device::Device,
12 error::{Error, Result},
13 ffi::c_void,
14 prelude::*,
15 revocable::Revocable,
16 sync::Arc,
17 types::ARef,
18};
19
20use core::ops::Deref;
21
22#[pin_data]
23struct DevresInner<T> {
24 dev: ARef<Device>,
25 callback: unsafe extern "C" fn(*mut c_void),
26 #[pin]
27 data: Revocable<T>,
28}
29
30/// This abstraction is meant to be used by subsystems to containerize [`Device`] bound resources to
31/// manage their lifetime.
32///
33/// [`Device`] bound resources should be freed when either the resource goes out of scope or the
34/// [`Device`] is unbound respectively, depending on what happens first.
35///
36/// To achieve that [`Devres`] registers a devres callback on creation, which is called once the
37/// [`Device`] is unbound, revoking access to the encapsulated resource (see also [`Revocable`]).
38///
39/// After the [`Devres`] has been unbound it is not possible to access the encapsulated resource
40/// anymore.
41///
42/// [`Devres`] users should make sure to simply free the corresponding backing resource in `T`'s
43/// [`Drop`] implementation.
44///
45/// # Example
46///
47/// ```no_run
48/// # use kernel::{bindings, c_str, device::Device, devres::Devres, io::{Io, IoRaw}};
49/// # use core::ops::Deref;
50///
51/// // See also [`pci::Bar`] for a real example.
52/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
53///
54/// impl<const SIZE: usize> IoMem<SIZE> {
55/// /// # Safety
56/// ///
57/// /// [`paddr`, `paddr` + `SIZE`) must be a valid MMIO region that is mappable into the CPUs
58/// /// virtual address space.
59/// unsafe fn new(paddr: usize) -> Result<Self>{
60/// // SAFETY: By the safety requirements of this function [`paddr`, `paddr` + `SIZE`) is
61/// // valid for `ioremap`.
62/// let addr = unsafe { bindings::ioremap(paddr as _, SIZE as _) };
63/// if addr.is_null() {
64/// return Err(ENOMEM);
65/// }
66///
67/// Ok(IoMem(IoRaw::new(addr as _, SIZE)?))
68/// }
69/// }
70///
71/// impl<const SIZE: usize> Drop for IoMem<SIZE> {
72/// fn drop(&mut self) {
73/// // SAFETY: `self.0.addr()` is guaranteed to be properly mapped by `Self::new`.
74/// unsafe { bindings::iounmap(self.0.addr() as _); };
75/// }
76/// }
77///
78/// impl<const SIZE: usize> Deref for IoMem<SIZE> {
79/// type Target = Io<SIZE>;
80///
81/// fn deref(&self) -> &Self::Target {
82/// // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
83/// unsafe { Io::from_raw(&self.0) }
84/// }
85/// }
86/// # fn no_run() -> Result<(), Error> {
87/// # // SAFETY: Invalid usage; just for the example to get an `ARef<Device>` instance.
88/// # let dev = unsafe { Device::get_device(core::ptr::null_mut()) };
89///
90/// // SAFETY: Invalid usage for example purposes.
91/// let iomem = unsafe { IoMem::<{ core::mem::size_of::<u32>() }>::new(0xBAAAAAAD)? };
92/// let devres = Devres::new(&dev, iomem, GFP_KERNEL)?;
93///
94/// let res = devres.try_access().ok_or(ENXIO)?;
95/// res.writel(0x42, 0x0);
96/// # Ok(())
97/// # }
98/// ```
99pub struct Devres<T>(Arc<DevresInner<T>>);
100
101impl<T> DevresInner<T> {
102 fn new(dev: &Device, data: T, flags: Flags) -> Result<Arc<DevresInner<T>>> {
103 let inner = Arc::pin_init(
104 pin_init!( DevresInner {
105 dev: dev.into(),
106 callback: Self::devres_callback,
107 data <- Revocable::new(data),
108 }),
109 flags,
110 )?;
111
112 // Convert `Arc<DevresInner>` into a raw pointer and make devres own this reference until
113 // `Self::devres_callback` is called.
114 let data = inner.clone().into_raw();
115
116 // SAFETY: `devm_add_action` guarantees to call `Self::devres_callback` once `dev` is
117 // detached.
118 let ret =
119 unsafe { bindings::devm_add_action(dev.as_raw(), Some(inner.callback), data as _) };
120
121 if ret != 0 {
122 // SAFETY: We just created another reference to `inner` in order to pass it to
123 // `bindings::devm_add_action`. If `bindings::devm_add_action` fails, we have to drop
124 // this reference accordingly.
125 let _ = unsafe { Arc::from_raw(data) };
126 return Err(Error::from_errno(ret));
127 }
128
129 Ok(inner)
130 }
131
132 fn as_ptr(&self) -> *const Self {
133 self as _
134 }
135
136 fn remove_action(this: &Arc<Self>) {
137 // SAFETY:
138 // - `self.inner.dev` is a valid `Device`,
139 // - the `action` and `data` pointers are the exact same ones as given to devm_add_action()
140 // previously,
141 // - `self` is always valid, even if the action has been released already.
142 let ret = unsafe {
143 bindings::devm_remove_action_nowarn(
144 this.dev.as_raw(),
145 Some(this.callback),
146 this.as_ptr() as _,
147 )
148 };
149
150 if ret == 0 {
151 // SAFETY: We leaked an `Arc` reference to devm_add_action() in `DevresInner::new`; if
152 // devm_remove_action_nowarn() was successful we can (and have to) claim back ownership
153 // of this reference.
154 let _ = unsafe { Arc::from_raw(this.as_ptr()) };
155 }
156 }
157
158 #[allow(clippy::missing_safety_doc)]
159 unsafe extern "C" fn devres_callback(ptr: *mut kernel::ffi::c_void) {
160 let ptr = ptr as *mut DevresInner<T>;
161 // Devres owned this memory; now that we received the callback, drop the `Arc` and hence the
162 // reference.
163 // SAFETY: Safe, since we leaked an `Arc` reference to devm_add_action() in
164 // `DevresInner::new`.
165 let inner = unsafe { Arc::from_raw(ptr) };
166
167 inner.data.revoke();
168 }
169}
170
171impl<T> Devres<T> {
172 /// Creates a new [`Devres`] instance of the given `data`. The `data` encapsulated within the
173 /// returned `Devres` instance' `data` will be revoked once the device is detached.
174 pub fn new(dev: &Device, data: T, flags: Flags) -> Result<Self> {
175 let inner = DevresInner::new(dev, data, flags)?;
176
177 Ok(Devres(inner))
178 }
179
180 /// Same as [`Devres::new`], but does not return a `Devres` instance. Instead the given `data`
181 /// is owned by devres and will be revoked / dropped, once the device is detached.
182 pub fn new_foreign_owned(dev: &Device, data: T, flags: Flags) -> Result {
183 let _ = DevresInner::new(dev, data, flags)?;
184
185 Ok(())
186 }
187}
188
189impl<T> Deref for Devres<T> {
190 type Target = Revocable<T>;
191
192 fn deref(&self) -> &Self::Target {
193 &self.0.data
194 }
195}
196
197impl<T> Drop for Devres<T> {
198 fn drop(&mut self) {
199 DevresInner::remove_action(&self.0);
200 }
201}