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device: rust: expand documentation for DeviceContext
Expand the documentation around DeviceContext states and types, in order to provide detailed information about their purpose and relationship with each other. Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com> Link: https://lore.kernel.org/r/20250722150110.23565-2-dakr@kernel.org [ Fix two minor typos. - Danilo ] Signed-off-by: Danilo Krummrich <dakr@kernel.org>
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@ -311,28 +311,75 @@ unsafe impl Send for Device {}
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// synchronization in `struct device`.
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unsafe impl Sync for Device {}
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/// Marker trait for the context of a bus specific device.
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/// Marker trait for the context or scope of a bus specific device.
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///
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/// Some functions of a bus specific device should only be called from a certain context, i.e. bus
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/// callbacks, such as `probe()`.
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/// [`DeviceContext`] is a marker trait for types representing the context of a bus specific
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/// [`Device`].
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///
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/// This is the marker trait for structures representing the context of a bus specific device.
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/// The specific device context types are: [`CoreInternal`], [`Core`], [`Bound`] and [`Normal`].
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///
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/// [`DeviceContext`] types are hierarchical, which means that there is a strict hierarchy that
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/// defines which [`DeviceContext`] type can be derived from another. For instance, any
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/// [`Device<Core>`] can dereference to a [`Device<Bound>`].
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///
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/// The following enumeration illustrates the dereference hierarchy of [`DeviceContext`] types.
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///
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/// - [`CoreInternal`] => [`Core`] => [`Bound`] => [`Normal`]
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///
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/// Bus devices can automatically implement the dereference hierarchy by using
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/// [`impl_device_context_deref`].
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///
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/// Note that the guarantee for a [`Device`] reference to have a certain [`DeviceContext`] comes
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/// from the specific scope the [`Device`] reference is valid in.
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///
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/// [`impl_device_context_deref`]: kernel::impl_device_context_deref
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pub trait DeviceContext: private::Sealed {}
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/// The [`Normal`] context is the context of a bus specific device when it is not an argument of
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/// any bus callback.
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/// The [`Normal`] context is the default [`DeviceContext`] of any [`Device`].
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///
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/// The normal context does not indicate any specific context. Any `Device<Ctx>` is also a valid
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/// [`Device<Normal>`]. It is the only [`DeviceContext`] for which it is valid to implement
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/// [`AlwaysRefCounted`] for.
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///
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/// [`AlwaysRefCounted`]: kernel::types::AlwaysRefCounted
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pub struct Normal;
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/// The [`Core`] context is the context of a bus specific device when it is supplied as argument of
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/// any of the bus callbacks, such as `probe()`.
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/// The [`Core`] context is the context of a bus specific device when it appears as argument of
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/// any bus specific callback, such as `probe()`.
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///
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/// The core context indicates that the [`Device<Core>`] reference's scope is limited to the bus
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/// callback it appears in. It is intended to be used for synchronization purposes. Bus device
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/// implementations can implement methods for [`Device<Core>`], such that they can only be called
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/// from bus callbacks.
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pub struct Core;
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/// Semantically the same as [`Core`] but reserved for internal usage of the corresponding bus
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/// Semantically the same as [`Core`], but reserved for internal usage of the corresponding bus
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/// abstraction.
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///
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/// The internal core context is intended to be used in exactly the same way as the [`Core`]
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/// context, with the difference that this [`DeviceContext`] is internal to the corresponding bus
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/// abstraction.
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///
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/// This context mainly exists to share generic [`Device`] infrastructure that should only be called
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/// from bus callbacks with bus abstractions, but without making them accessible for drivers.
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pub struct CoreInternal;
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/// The [`Bound`] context is the context of a bus specific device reference when it is guaranteed to
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/// be bound for the duration of its lifetime.
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/// The [`Bound`] context is the [`DeviceContext`] of a bus specific device when it is guaranteed to
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/// be bound to a driver.
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///
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/// The bound context indicates that for the entire duration of the lifetime of a [`Device<Bound>`]
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/// reference, the [`Device`] is guaranteed to be bound to a driver.
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///
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/// Some APIs, such as [`dma::CoherentAllocation`] or [`Devres`] rely on the [`Device`] to be bound,
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/// which can be proven with the [`Bound`] device context.
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///
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/// Any abstraction that can guarantee a scope where the corresponding bus device is bound, should
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/// provide a [`Device<Bound>`] reference to its users for this scope. This allows users to benefit
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/// from optimizations for accessing device resources, see also [`Devres::access`].
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///
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/// [`Devres`]: kernel::devres::Devres
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/// [`Devres::access`]: kernel::devres::Devres::access
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/// [`dma::CoherentAllocation`]: kernel::dma::CoherentAllocation
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pub struct Bound;
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mod private {
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