Re: [PATCH RFC v6 03/26] rust: gpu: Add GPU buddy allocator bindings

+///
+/// These flags control the allocation behavior of the buddy allocator.
+#[derive(Clone, Copy, Default, PartialEq, Eq)]
+pub struct BuddyFlags(usize);
+
+impl BuddyFlags {
+    /// Range-based allocation from start to end addresses.
+    pub const RANGE_ALLOCATION: usize = bindings::GPU_BUDDY_RANGE_ALLOCATION;
+
+    /// Allocate from top of address space downward.
+    pub const TOPDOWN_ALLOCATION: usize = bindings::GPU_BUDDY_TOPDOWN_ALLOCATION;
+
+    /// Allocate physically contiguous blocks.
+    pub const CONTIGUOUS_ALLOCATION: usize = bindings::GPU_BUDDY_CONTIGUOUS_ALLOCATION;
+
+    /// Request allocation from the cleared (zeroed) memory. The zero'ing is not
+    /// done by the allocator, but by the caller before freeing old blocks.
+    pub const CLEAR_ALLOCATION: usize = bindings::GPU_BUDDY_CLEAR_ALLOCATION;
+
+    /// Disable trimming of partially used blocks.
+    pub const TRIM_DISABLE: usize = bindings::GPU_BUDDY_TRIM_DISABLE;
+
+    /// Mark blocks as cleared (zeroed) when freeing. When set during free,
+    /// indicates that the caller has already zeroed the memory.
+    pub const CLEARED: usize = bindings::GPU_BUDDY_CLEARED;
+
+    /// Create [`BuddyFlags`] from a raw value with validation.
+    ///
+    /// Use `|` operator to combine flags if needed, before calling this method.
+    pub fn try_new(flags: usize) -> Result<Self> {
+        // Flags must not exceed u32::MAX to satisfy the GPU buddy allocator C API.
+        if flags > u32::MAX as usize {
+            return Err(EINVAL);
+        }
+
+        // `TOPDOWN_ALLOCATION` only works without `RANGE_ALLOCATION`. When both are
+        // set, `TOPDOWN_ALLOCATION` is silently ignored by the allocator. Reject this.
+        if (flags & Self::RANGE_ALLOCATION) != 0 && (flags & Self::TOPDOWN_ALLOCATION) != 0 {
+            return Err(EINVAL);
+        }
+
+        Ok(Self(flags))
+    }
+
+    /// Get raw value of the flags.
+    pub(crate) fn as_raw(self) -> usize {
+        self.0
+    }
+}
+
+/// Parameters for creating a GPU buddy allocator.
+#[derive(Clone, Copy)]
+pub struct GpuBuddyParams {
+    /// Base offset in bytes where the managed memory region starts.
+    /// Allocations will be offset by this value.
+    pub base_offset_bytes: u64,
+    /// Total physical memory size managed by the allocator in bytes.
+    pub physical_memory_size_bytes: u64,
+    /// Minimum allocation unit / chunk size in bytes, must be >= 4KB.
+    pub chunk_size_bytes: u64,
+}
+
+/// Parameters for allocating blocks from a GPU buddy allocator.
+#[derive(Clone, Copy)]
+pub struct GpuBuddyAllocParams {
+    /// Start of allocation range in bytes. Use 0 for beginning.
+    pub start_range_address: u64,
+    /// End of allocation range in bytes. Use 0 for entire range.
+    pub end_range_address: u64,
+    /// Total size to allocate in bytes.
+    pub size_bytes: u64,
+    /// Minimum block size for fragmented allocations in bytes.
+    pub min_block_size_bytes: u64,
+    /// Buddy allocator behavior flags.
+    pub buddy_flags: BuddyFlags,
+}
+

(not a full review)

Any reason these two need Clone, Copy? I'm not seeing a use case for
that, maybe we should pass them as non-mutable references, but I don't
think there is any point in passing them by value ever.

Dave.