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| -rw-r--r-- | rust/kernel/device.rs | 139 |
1 files changed, 126 insertions, 13 deletions
diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs index fe095a8eccb1..5902b3714a16 100644 --- a/rust/kernel/device.rs +++ b/rust/kernel/device.rs @@ -15,23 +15,130 @@ use crate::c_str; pub mod property; -/// A reference-counted device. +/// The core representation of a device in the kernel's driver model. /// -/// This structure represents the Rust abstraction for a C `struct device`. This implementation -/// abstracts the usage of an already existing C `struct device` within Rust code that we get -/// passed from the C side. +/// This structure represents the Rust abstraction for a C `struct device`. A [`Device`] can either +/// exist as temporary reference (see also [`Device::from_raw`]), which is only valid within a +/// certain scope or as [`ARef<Device>`], owning a dedicated reference count. /// -/// An instance of this abstraction can be obtained temporarily or permanent. +/// # Device Types /// -/// A temporary one is bound to the lifetime of the C `struct device` pointer used for creation. -/// A permanent instance is always reference-counted and hence not restricted by any lifetime -/// boundaries. +/// A [`Device`] can represent either a bus device or a class device. /// -/// For subsystems it is recommended to create a permanent instance to wrap into a subsystem -/// specific device structure (e.g. `pci::Device`). This is useful for passing it to drivers in -/// `T::probe()`, such that a driver can store the `ARef<Device>` (equivalent to storing a -/// `struct device` pointer in a C driver) for arbitrary purposes, e.g. allocating DMA coherent -/// memory. +/// ## Bus Devices +/// +/// A bus device is a [`Device`] that is associated with a physical or virtual bus. Examples of +/// buses include PCI, USB, I2C, and SPI. Devices attached to a bus are registered with a specific +/// bus type, which facilitates matching devices with appropriate drivers based on IDs or other +/// identifying information. Bus devices are visible in sysfs under `/sys/bus/<bus-name>/devices/`. +/// +/// ## Class Devices +/// +/// A class device is a [`Device`] that is associated with a logical category of functionality +/// rather than a physical bus. Examples of classes include block devices, network interfaces, sound +/// cards, and input devices. Class devices are grouped under a common class and exposed to +/// userspace via entries in `/sys/class/<class-name>/`. +/// +/// # Device Context +/// +/// [`Device`] references are generic over a [`DeviceContext`], which represents the type state of +/// a [`Device`]. +/// +/// As the name indicates, this type state represents the context of the scope the [`Device`] +/// reference is valid in. For instance, the [`Bound`] context guarantees that the [`Device`] is +/// bound to a driver for the entire duration of the existence of a [`Device<Bound>`] reference. +/// +/// Other [`DeviceContext`] types besides [`Bound`] are [`Normal`], [`Core`] and [`CoreInternal`]. +/// +/// Unless selected otherwise [`Device`] defaults to the [`Normal`] [`DeviceContext`], which by +/// itself has no additional requirements. +/// +/// It is always up to the caller of [`Device::from_raw`] to select the correct [`DeviceContext`] +/// type for the corresponding scope the [`Device`] reference is created in. +/// +/// All [`DeviceContext`] types other than [`Normal`] are intended to be used with +/// [bus devices](#bus-devices) only. +/// +/// # Implementing Bus Devices +/// +/// This section provides a guideline to implement bus specific devices, such as [`pci::Device`] or +/// [`platform::Device`]. +/// +/// A bus specific device should be defined as follows. +/// +/// ```ignore +/// #[repr(transparent)] +/// pub struct Device<Ctx: device::DeviceContext = device::Normal>( +/// Opaque<bindings::bus_device_type>, +/// PhantomData<Ctx>, +/// ); +/// ``` +/// +/// Since devices are reference counted, [`AlwaysRefCounted`] should be implemented for `Device` +/// (i.e. `Device<Normal>`). Note that [`AlwaysRefCounted`] must not be implemented for any other +/// [`DeviceContext`], since all other device context types are only valid within a certain scope. +/// +/// In order to be able to implement the [`DeviceContext`] dereference hierarchy, bus device +/// implementations should call the [`impl_device_context_deref`] macro as shown below. +/// +/// ```ignore +/// // SAFETY: `Device` is a transparent wrapper of a type that doesn't depend on `Device`'s +/// // generic argument. +/// kernel::impl_device_context_deref!(unsafe { Device }); +/// ``` +/// +/// In order to convert from a any [`Device<Ctx>`] to [`ARef<Device>`], bus devices can implement +/// the following macro call. +/// +/// ```ignore +/// kernel::impl_device_context_into_aref!(Device); +/// ``` +/// +/// Bus devices should also implement the following [`AsRef`] implementation, such that users can +/// easily derive a generic [`Device`] reference. +/// +/// ```ignore +/// impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> { +/// fn as_ref(&self) -> &device::Device<Ctx> { +/// ... +/// } +/// } +/// ``` +/// +/// # Implementing Class Devices +/// +/// Class device implementations require less infrastructure and depend slightly more on the +/// specific subsystem. +/// +/// An example implementation for a class device could look like this. +/// +/// ```ignore +/// #[repr(C)] +/// pub struct Device<T: class::Driver> { +/// dev: Opaque<bindings::class_device_type>, +/// data: T::Data, +/// } +/// ``` +/// +/// This class device uses the sub-classing pattern to embed the driver's private data within the +/// allocation of the class device. For this to be possible the class device is generic over the +/// class specific `Driver` trait implementation. +/// +/// Just like any device, class devices are reference counted and should hence implement +/// [`AlwaysRefCounted`] for `Device`. +/// +/// Class devices should also implement the following [`AsRef`] implementation, such that users can +/// easily derive a generic [`Device`] reference. +/// +/// ```ignore +/// impl<T: class::Driver> AsRef<device::Device> for Device<T> { +/// fn as_ref(&self) -> &device::Device { +/// ... +/// } +/// } +/// ``` +/// +/// An example for a class device implementation is [`drm::Device`]. /// /// # Invariants /// @@ -42,6 +149,12 @@ pub mod property; /// /// `bindings::device::release` is valid to be called from any thread, hence `ARef<Device>` can be /// dropped from any thread. +/// +/// [`AlwaysRefCounted`]: kernel::types::AlwaysRefCounted +/// [`drm::Device`]: kernel::drm::Device +/// [`impl_device_context_deref`]: kernel::impl_device_context_deref +/// [`pci::Device`]: kernel::pci::Device +/// [`platform::Device`]: kernel::platform::Device #[repr(transparent)] pub struct Device<Ctx: DeviceContext = Normal>(Opaque<bindings::device>, PhantomData<Ctx>); |