[PATCH 5/5] rust: drm: add KUnit tests for panel

[Albert Esteve <aesteve@redhat.com>]

Add a test module to verify basic data type conversions
and layout. The tests covers:

- PanelOrientation and ConnectorType: TryFrom conversion for valid
  values and also out-of-range invalid inputs.
- PanelContainer: layout invariants (offset, alignment, size) on which
  Panel::new relies on for memory access.

Tests are gated on CONFIG_RUST_DRM_PANEL_KUNIT_TEST.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 rust/kernel/Kconfig.test | 10 ++++++
 rust/kernel/drm/panel.rs | 87 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)

diff --git a/rust/kernel/Kconfig.test b/rust/kernel/Kconfig.test
index e6a5c7a795f0f..397b916dca0d4 100644
--- a/rust/kernel/Kconfig.test
+++ b/rust/kernel/Kconfig.test
@@ -83,4 +83,14 @@ config RUST_BITFIELD_KUNIT_TEST
 
 	  If unsure, say N.
 
+config RUST_DRM_PANEL_KUNIT_TEST
+	bool "KUnit tests for Rust panel API" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables KUnit tests for the Rust panel API.
+	  These are only for development and testing, not for regular
+	  kernel use cases.
+
+	  If unsure, say N.
+
 endif
diff --git a/rust/kernel/drm/panel.rs b/rust/kernel/drm/panel.rs
index 8f87774e06ed7..3da203c39edd6 100644
--- a/rust/kernel/drm/panel.rs
+++ b/rust/kernel/drm/panel.rs
@@ -595,3 +595,90 @@ pub(crate) const fn build() -> &'static bindings::drm_panel_funcs {
         &Self::VTABLE
     }
 }
+
+#[cfg(CONFIG_RUST_DRM_PANEL_KUNIT_TEST)]
+#[macros::kunit_tests(rust_kernel_drm_panel)]
+mod tests {
+    use super::*;
+    use core::mem::{align_of, offset_of, size_of, ManuallyDrop, MaybeUninit};
+
+    struct TestData {
+        _ptr: *const u8,
+        _byte: u8,
+    }
+
+    #[test]
+    fn panel_orientation() {
+        // Test valid values.
+        assert!(matches!(
+            PanelOrientation::try_from(-1),
+            Ok(PanelOrientation::Unknown)
+        ));
+        assert!(matches!(
+            PanelOrientation::try_from(0),
+            Ok(PanelOrientation::Normal)
+        ));
+        assert!(matches!(
+            PanelOrientation::try_from(1),
+            Ok(PanelOrientation::BottomUp)
+        ));
+        assert!(matches!(
+            PanelOrientation::try_from(2),
+            Ok(PanelOrientation::LeftUp)
+        ));
+        assert!(matches!(
+            PanelOrientation::try_from(3),
+            Ok(PanelOrientation::RightUp)
+        ));
+
+        // Test invalid values.
+        assert!(PanelOrientation::try_from(4).is_err());
+        assert!(PanelOrientation::try_from(-2).is_err());
+    }
+
+    #[test]
+    fn connector_type() {
+        // Test valid values.
+        assert!(matches!(
+            ConnectorType::try_from(0),
+            Ok(ConnectorType::Unknown)
+        ));
+        assert!(matches!(
+            ConnectorType::try_from(10),
+            Ok(ConnectorType::DisplayPort)
+        ));
+        assert!(matches!(
+            ConnectorType::try_from(14),
+            Ok(ConnectorType::eDP)
+        ));
+        assert!(matches!(
+            ConnectorType::try_from(16),
+            Ok(ConnectorType::DSI)
+        ));
+        assert!(matches!(
+            ConnectorType::try_from(20),
+            Ok(ConnectorType::USB)
+        ));
+
+        // Test invalid values.
+        assert!(ConnectorType::try_from(21).is_err());
+    }
+
+    #[test]
+    fn panel_container_layout() {
+        assert_eq!(offset_of!(PanelContainer<TestData>, data), 0);
+
+        assert_eq!(size_of::<ManuallyDrop<TestData>>(), size_of::<TestData>());
+
+        let panel_offset = offset_of!(PanelContainer<TestData>, panel);
+        assert_eq!(
+            panel_offset % align_of::<MaybeUninit<bindings::drm_panel>>(),
+            0
+        );
+
+        assert!(
+            size_of::<PanelContainer<TestData>>()
+                >= panel_offset + size_of::<bindings::drm_panel>()
+        );
+    }
+}

-- 
2.55.0