rust: add device::Data.

This allows access to registrations and io resources to be automatically
revoked when devices are removed, even if the ref count to their state
is non-zero.

This is the last piece needed by the PL061 driver.

Signed-off-by: Wedson Almeida Filho <[email protected]>

rust/kernel/device.rs

@@ -4,7 +4,17 @@
 //!
 //! C header: [`include/linux/device.h`](../../../../include/linux/device.h)
 
-use crate::{bindings, str::CStr};
+use crate::{
+    bindings,
+    revocable::{Revocable, RevocableGuard},
+    str::CStr,
+    sync::{NeedsLockClass, RevocableMutex, RevocableMutexGuard, UniqueRef},
+    Result,
+};
+use core::{
+    ops::{Deref, DerefMut},
+    pin::Pin,
+};
 
 /// A raw device.
 ///
@@ -74,3 +84,123 @@ impl Drop for Device {
         unsafe { bindings::put_device(self.ptr) };
     }
 }
+
+/// Device data.
+///
+/// When a device is removed (for whatever reason, for example, because the device was unplugged or
+/// because the user decided to unbind the driver), the driver is given a chance to clean its state
+/// up, and all io resources should ideally not be used anymore.
+///
+/// However, the device data is reference-counted because other subsystems hold pointers to it. So
+/// some device state must be freed and not used anymore, while others must remain accessible.
+///
+/// This struct separates the device data into three categories:
+/// 1. Registrations: are destroyed when the device is removed, but before the io resources
+///    become inaccessible.
+/// 2. Io resources: are available until the device is removed.
+/// 3. General data: remain available as long as the ref count is nonzero.
+///
+/// This struct implements the `DeviceRemoval` trait so that it can clean resources up even if not
+/// explicitly called by the device drivers.
+pub struct Data<T, U, V> {
+    registrations: RevocableMutex<T>,
+    resources: Revocable<U>,
+    general: V,
+}
+
+/// Safely creates an new reference-counted instance of [`Data`].
+#[doc(hidden)]
+#[macro_export]
+macro_rules! new_device_data {
+    ($reg:expr, $res:expr, $gen:expr, $name:literal) => {{
+        static mut CLASS1: core::mem::MaybeUninit<$crate::bindings::lock_class_key> =
+            core::mem::MaybeUninit::uninit();
+        static mut CLASS2: core::mem::MaybeUninit<$crate::bindings::lock_class_key> =
+            core::mem::MaybeUninit::uninit();
+        let regs = $reg;
+        let res = $res;
+        let gen = $gen;
+        let name = $crate::c_str!($name);
+        // SAFETY: `CLASS1` and `CLASS2` are never used by Rust code directly; the C portion of the
+        // kernel may change it though.
+        unsafe {
+            $crate::device::Data::try_new(
+                regs,
+                res,
+                gen,
+                name,
+                CLASS1.as_mut_ptr(),
+                CLASS2.as_mut_ptr(),
+            )
+        }
+    }};
+}
+
+impl<T, U, V> Data<T, U, V> {
+    /// Creates a new instance of `Data`.
+    ///
+    /// It is recommended that the [`new_device_data`] macro be used as it automatically creates
+    /// the lock classes.
+    ///
+    /// # Safety
+    ///
+    /// `key1` and `key2` must point to valid memory locations and remain valid until `self` is
+    /// dropped.
+    pub unsafe fn try_new(
+        registrations: T,
+        resources: U,
+        general: V,
+        name: &'static CStr,
+        key1: *mut bindings::lock_class_key,
+        key2: *mut bindings::lock_class_key,
+    ) -> Result<Pin<UniqueRef<Self>>> {
+        let mut ret = Pin::from(UniqueRef::try_new(Self {
+            // SAFETY: We call `RevocableMutex::init` below.
+            registrations: unsafe { RevocableMutex::new(registrations) },
+            resources: Revocable::new(resources),
+            general,
+        })?);
+
+        // SAFETY: `Data::registrations` is pinned when `Data` is.
+        let pinned = unsafe { ret.as_mut().map_unchecked_mut(|d| &mut d.registrations) };
+
+        // SAFETY: The safety requirements of this function satisfy those of `RevocableMutex::init`.
+        unsafe { pinned.init(name, key1, key2) };
+        Ok(ret)
+    }
+
+    /// Returns the resources if they're still available.
+    pub fn resources(&self) -> Option<RevocableGuard<'_, U>> {
+        self.resources.try_access()
+    }
+
+    /// Returns the locked registrations if they're still available.
+    pub fn registrations(&self) -> Option<RevocableMutexGuard<'_, T>> {
+        self.registrations.try_lock()
+    }
+}
+
+impl<T, U, V> crate::driver::DeviceRemoval for Data<T, U, V> {
+    fn device_remove(&self) {
+        // We revoke the registrations first so that resources are still available to them during
+        // unregistration.
+        self.registrations.revoke();
+
+        // Release resources now. General data remains available.
+        self.resources.revoke();
+    }
+}
+
+impl<T, U, V> Deref for Data<T, U, V> {
+    type Target = V;
+
+    fn deref(&self) -> &V {
+        &self.general
+    }
+}
+
+impl<T, U, V> DerefMut for Data<T, U, V> {
+    fn deref_mut(&mut self) -> &mut V {
+        &mut self.general
+    }
+}