spi: aspeed: Improve handling of shared SPI

Merge series from Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>:

This patch series improves handling of SPI controllers that are
shared by spi-mem devices and other SPI peripherals.

The primary goal of this series is to support non-spi-mem devices in
the ASPEED FMC/SPI controller driver. It also addresses an issue in
the spi-mem framework observed when different types of SPI devices
operate concurrently on the same controller, ensuring that spi-mem
operations are properly serialized.

1 files changed, 11 insertions, 9 deletions

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 71b200df0f40..031720bf5d8c 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -232,30 +232,32 @@ impl Device<CoreInternal> {
     ///
     /// # Safety
     ///
-    /// - Must only be called once after a preceding call to [`Device::set_drvdata`].
     /// - The type `T` must match the type of the `ForeignOwnable` previously stored by
     ///   [`Device::set_drvdata`].
-    pub unsafe fn drvdata_obtain<T: 'static>(&self) -> Pin<KBox<T>> {
+    pub(crate) unsafe fn drvdata_obtain<T: 'static>(&self) -> Option<Pin<KBox<T>>> {
         // SAFETY: By the type invariants, `self.as_raw()` is a valid pointer to a `struct device`.
         let ptr = unsafe { bindings::dev_get_drvdata(self.as_raw()) };
 
         // SAFETY: By the type invariants, `self.as_raw()` is a valid pointer to a `struct device`.
         unsafe { bindings::dev_set_drvdata(self.as_raw(), core::ptr::null_mut()) };
 
+        if ptr.is_null() {
+            return None;
+        }
+
         // SAFETY:
-        // - By the safety requirements of this function, `ptr` comes from a previous call to
-        //   `into_foreign()`.
+        // - If `ptr` is not NULL, it comes from a previous call to `into_foreign()`.
         // - `dev_get_drvdata()` guarantees to return the same pointer given to `dev_set_drvdata()`
         //   in `into_foreign()`.
-        unsafe { Pin::<KBox<T>>::from_foreign(ptr.cast()) }
+        Some(unsafe { Pin::<KBox<T>>::from_foreign(ptr.cast()) })
     }
 
     /// Borrow the driver's private data bound to this [`Device`].
     ///
     /// # Safety
     ///
-    /// - Must only be called after a preceding call to [`Device::set_drvdata`] and before
-    ///   [`Device::drvdata_obtain`].
+    /// - Must only be called after a preceding call to [`Device::set_drvdata`] and before the
+    ///   device is fully unbound.
     /// - The type `T` must match the type of the `ForeignOwnable` previously stored by
     ///   [`Device::set_drvdata`].
     pub unsafe fn drvdata_borrow<T: 'static>(&self) -> Pin<&T> {
@@ -271,7 +273,7 @@ impl Device<Bound> {
     /// # Safety
     ///
     /// - Must only be called after a preceding call to [`Device::set_drvdata`] and before
-    ///   [`Device::drvdata_obtain`].
+    ///   the device is fully unbound.
     /// - The type `T` must match the type of the `ForeignOwnable` previously stored by
     ///   [`Device::set_drvdata`].
     unsafe fn drvdata_unchecked<T: 'static>(&self) -> Pin<&T> {
@@ -320,7 +322,7 @@ impl Device<Bound> {
 
         // SAFETY:
         // - The above check of `dev_get_drvdata()` guarantees that we are called after
-        //   `set_drvdata()` and before `drvdata_obtain()`.
+        //   `set_drvdata()`.
         // - We've just checked that the type of the driver's private data is in fact `T`.
         Ok(unsafe { self.drvdata_unchecked() })
     }