rust: auxiliary: consider auxiliary devices always have a parent

An auxiliary device is guaranteed to always have a parent device (both
in C and Rust), hence don't return an Option<&auxiliary::Device> in
auxiliary::Device::parent().

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

drivers/gpu/drm/nova/file.rs

@@ -28,7 +28,7 @@ impl File {
         _file: &drm::File<File>,
     ) -> Result<u32> {
         let adev = &dev.adev;
-        let parent = adev.parent().ok_or(ENOENT)?;
+        let parent = adev.parent();
         let pdev: &pci::Device = parent.try_into()?;
 
         let value = match getparam.param as u32 {

rust/kernel/auxiliary.rs

@@ -215,9 +215,10 @@ impl<Ctx: device::DeviceContext> Device<Ctx> {
         unsafe { (*self.as_raw()).id }
     }
 
-    /// Returns a reference to the parent [`device::Device`], if any.
-    pub fn parent(&self) -> Option<&device::Device> {
-        self.as_ref().parent()
+    /// Returns a reference to the parent [`device::Device`].
+    pub fn parent(&self) -> &device::Device {
+        // SAFETY: A `struct auxiliary_device` always has a parent.
+        unsafe { self.as_ref().parent().unwrap_unchecked() }
     }
 }
 

samples/rust/rust_driver_auxiliary.rs

@@ -68,7 +68,7 @@ impl pci::Driver for ParentDriver {
 
 impl ParentDriver {
     fn connect(adev: &auxiliary::Device) -> Result<()> {
-        let parent = adev.parent().ok_or(EINVAL)?;
+        let parent = adev.parent();
         let pdev: &pci::Device = parent.try_into()?;
 
         let vendor = pdev.vendor_id();