[PATCH RFC 4/4] samples: rust: Add sample demonstrating DRM buddy allocator

[Joel Fernandes <joelagnelf@nvidia.com>]

Demonstrates usage of the DRM buddy allocator bindings through
a simple test module that initializes the allocator, performs
allocations, and prints information about the allocated blocks.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
 samples/rust/Kconfig           |  14 +++++
 samples/rust/Makefile          |   1 +
 samples/rust/rust_drm_buddy.rs | 106 +++++++++++++++++++++++++++++++++
 3 files changed, 121 insertions(+)
 create mode 100644 samples/rust/rust_drm_buddy.rs

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index b45631e2593c..8ccb4064ba91 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -21,6 +21,20 @@ config SAMPLE_RUST_CLIST
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DRM_BUDDY
+	tristate "DRM buddy allocator sample"
+	depends on DRM_BUDDY
+	help
+	  This option builds the Rust DRM buddy allocator sample.
+
+	  The sample demonstrates using the DRM buddy allocator bindings
+	  to allocate and free memory blocks.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_drm_buddy.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_CONFIGFS
 	tristate "Configfs sample"
 	depends on CONFIGFS_FS
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index f8899c0df762..a56204ee4e96 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -2,6 +2,7 @@
 ccflags-y += -I$(src)				# needed for trace events
 
 obj-$(CONFIG_SAMPLE_RUST_CLIST)			+= rust_clist.o
+obj-$(CONFIG_SAMPLE_RUST_DRM_BUDDY)		+= rust_drm_buddy.o
 obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
 obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
diff --git a/samples/rust/rust_drm_buddy.rs b/samples/rust/rust_drm_buddy.rs
new file mode 100644
index 000000000000..96907bc19243
--- /dev/null
+++ b/samples/rust/rust_drm_buddy.rs
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust DRM buddy allocator sample.
+//!
+//! This sample demonstrates using the DRM buddy allocator from Rust.
+
+use kernel::{
+    drm::buddy::{
+        BuddyFlags,
+        DrmBuddy, //
+    },
+    prelude::*,
+    sizes::*, //
+};
+
+module! {
+    type: RustDrmBuddySample,
+    name: "rust_drm_buddy",
+    authors: ["Joel Fernandes"],
+    description: "DRM buddy allocator sample",
+    license: "GPL",
+}
+
+struct RustDrmBuddySample;
+
+impl kernel::Module for RustDrmBuddySample {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        // Create a buddy allocator managing 1GB with 4KB chunks.
+        let buddy = DrmBuddy::new(SZ_1G, SZ_4K)?;
+
+        pr_info!("=== Test 1: Single 16MB block ===\n");
+        let allocated = buddy.alloc_blocks(
+            0,
+            0,
+            SZ_16M,
+            SZ_4K,
+            BuddyFlags::RANGE_ALLOCATION,
+            GFP_KERNEL,
+        )?;
+
+        let mut count = 0;
+        for block in &allocated {
+            pr_info!(
+                "  Block {}: offset=0x{:x}, order={}, size={}\n",
+                count,
+                block.offset(),
+                block.order(),
+                block.size(&buddy)
+            );
+            count += 1;
+        }
+        pr_info!("  Total: {} blocks\n", count);
+        drop(allocated);
+
+        pr_info!("=== Test 2: Three 4MB blocks ===\n");
+        let allocated = buddy.alloc_blocks(
+            0,
+            0,
+            SZ_4M * 3,
+            SZ_4K,
+            BuddyFlags::RANGE_ALLOCATION,
+            GFP_KERNEL,
+        )?;
+
+        count = 0;
+        for block in &allocated {
+            pr_info!(
+                "  Block {}: offset=0x{:x}, order={}, size={}\n",
+                count,
+                block.offset(),
+                block.order(),
+                block.size(&buddy)
+            );
+            count += 1;
+        }
+        pr_info!("  Total: {} blocks\n", count);
+        drop(allocated);
+
+        pr_info!("=== Test 3: Two 8MB blocks ===\n");
+        let allocated = buddy.alloc_blocks(
+            0,
+            0,
+            SZ_8M * 2,
+            SZ_4K,
+            BuddyFlags::RANGE_ALLOCATION,
+            GFP_KERNEL,
+        )?;
+
+        count = 0;
+        for block in &allocated {
+            pr_info!(
+                "  Block {}: offset=0x{:x}, order={}, size={}\n",
+                count,
+                block.offset(),
+                block.order(),
+                block.size(&buddy)
+            );
+            count += 1;
+        }
+        pr_info!("  Total: {} blocks\n", count);
+
+        pr_info!("=== All tests passed! ===\n");
+
+        Ok(RustDrmBuddySample {})
+    }
+}
-- 
2.34.1