1 // SPDX-License-Identifier: GPL-2.0 2 3 //! Generic devices that are part of the kernel's driver model. 4 //! 5 //! C header: [`include/linux/device.h`](srctree/include/linux/device.h) 6 7 use crate::{ 8 bindings, 9 types::{ARef, Opaque}, 10 }; 11 use core::ptr; 12 13 /// A reference-counted device. 14 /// 15 /// This structure represents the Rust abstraction for a C `struct device`. This implementation 16 /// abstracts the usage of an already existing C `struct device` within Rust code that we get 17 /// passed from the C side. 18 /// 19 /// An instance of this abstraction can be obtained temporarily or permanent. 20 /// 21 /// A temporary one is bound to the lifetime of the C `struct device` pointer used for creation. 22 /// A permanent instance is always reference-counted and hence not restricted by any lifetime 23 /// boundaries. 24 /// 25 /// For subsystems it is recommended to create a permanent instance to wrap into a subsystem 26 /// specific device structure (e.g. `pci::Device`). This is useful for passing it to drivers in 27 /// `T::probe()`, such that a driver can store the `ARef<Device>` (equivalent to storing a 28 /// `struct device` pointer in a C driver) for arbitrary purposes, e.g. allocating DMA coherent 29 /// memory. 30 /// 31 /// # Invariants 32 /// 33 /// A `Device` instance represents a valid `struct device` created by the C portion of the kernel. 34 /// 35 /// Instances of this type are always reference-counted, that is, a call to `get_device` ensures 36 /// that the allocation remains valid at least until the matching call to `put_device`. 37 /// 38 /// `bindings::device::release` is valid to be called from any thread, hence `ARef<Device>` can be 39 /// dropped from any thread. 40 #[repr(transparent)] 41 pub struct Device(Opaque<bindings::device>); 42 43 impl Device { 44 /// Creates a new reference-counted abstraction instance of an existing `struct device` pointer. 45 /// 46 /// # Safety 47 /// 48 /// Callers must ensure that `ptr` is valid, non-null, and has a non-zero reference count, 49 /// i.e. it must be ensured that the reference count of the C `struct device` `ptr` points to 50 /// can't drop to zero, for the duration of this function call. 51 /// 52 /// It must also be ensured that `bindings::device::release` can be called from any thread. 53 /// While not officially documented, this should be the case for any `struct device`. get_device(ptr: *mut bindings::device) -> ARef<Self>54 pub unsafe fn get_device(ptr: *mut bindings::device) -> ARef<Self> { 55 // SAFETY: By the safety requirements ptr is valid 56 unsafe { Self::as_ref(ptr) }.into() 57 } 58 59 /// Obtain the raw `struct device *`. as_raw(&self) -> *mut bindings::device60 pub(crate) fn as_raw(&self) -> *mut bindings::device { 61 self.0.get() 62 } 63 64 /// Convert a raw C `struct device` pointer to a `&'a Device`. 65 /// 66 /// # Safety 67 /// 68 /// Callers must ensure that `ptr` is valid, non-null, and has a non-zero reference count, 69 /// i.e. it must be ensured that the reference count of the C `struct device` `ptr` points to 70 /// can't drop to zero, for the duration of this function call and the entire duration when the 71 /// returned reference exists. as_ref<'a>(ptr: *mut bindings::device) -> &'a Self72 pub unsafe fn as_ref<'a>(ptr: *mut bindings::device) -> &'a Self { 73 // SAFETY: Guaranteed by the safety requirements of the function. 74 unsafe { &*ptr.cast() } 75 } 76 } 77 78 // SAFETY: Instances of `Device` are always reference-counted. 79 unsafe impl crate::types::AlwaysRefCounted for Device { inc_ref(&self)80 fn inc_ref(&self) { 81 // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. 82 unsafe { bindings::get_device(self.as_raw()) }; 83 } 84 dec_ref(obj: ptr::NonNull<Self>)85 unsafe fn dec_ref(obj: ptr::NonNull<Self>) { 86 // SAFETY: The safety requirements guarantee that the refcount is non-zero. 87 unsafe { bindings::put_device(obj.cast().as_ptr()) } 88 } 89 } 90 91 // SAFETY: As by the type invariant `Device` can be sent to any thread. 92 unsafe impl Send for Device {} 93 94 // SAFETY: `Device` can be shared among threads because all immutable methods are protected by the 95 // synchronization in `struct device`. 96 unsafe impl Sync for Device {} 97