[PATCH RFC 09/18] rust: drm: syncobj: Add DRM Sync Object abstraction

[Asahi Lina]

DRM Sync Objects are a container for a DMA fence, and can be waited on
signaled, exported, and imported from userspace. Add a Rust abstraction
so Rust DRM drivers can support this functionality.

Signed-off-by: Asahi Lina <lina@xxxxxxxxxxxxx>
---
 rust/bindings/bindings_helper.h |  1 +
 rust/helpers.c                  | 19 ++++++++++
 rust/kernel/drm/mod.rs          |  1 +
 rust/kernel/drm/syncobj.rs      | 77 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 98 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 705af292a5b4..b6696011f3a4 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -12,6 +12,7 @@
 #include <drm/drm_gem.h>
 #include <drm/drm_gem_shmem_helper.h>
 #include <drm/drm_ioctl.h>
+#include <drm/drm_syncobj.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/dma-fence.h>
diff --git a/rust/helpers.c b/rust/helpers.c
index 8e906a7a7d8a..11965b1e2f4e 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -20,6 +20,7 @@
 
 #include <drm/drm_gem.h>
 #include <drm/drm_gem_shmem_helper.h>
+#include <drm/drm_syncobj.h>
 #include <linux/bug.h>
 #include <linux/build_bug.h>
 #include <linux/device.h>
@@ -461,6 +462,24 @@ __u64 rust_helper_drm_vma_node_offset_addr(struct drm_vma_offset_node *node)
 }
 EXPORT_SYMBOL_GPL(rust_helper_drm_vma_node_offset_addr);
 
+void rust_helper_drm_syncobj_get(struct drm_syncobj *obj)
+{
+	drm_syncobj_get(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_syncobj_get);
+
+void rust_helper_drm_syncobj_put(struct drm_syncobj *obj)
+{
+	drm_syncobj_put(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_syncobj_put);
+
+struct dma_fence *rust_helper_drm_syncobj_fence_get(struct drm_syncobj *syncobj)
+{
+	return drm_syncobj_fence_get(syncobj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_syncobj_fence_get);
+
 #ifdef CONFIG_DRM_GEM_SHMEM_HELPER
 
 void rust_helper_drm_gem_shmem_object_free(struct drm_gem_object *obj)
diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
index 73fab2dee3af..dae98826edfd 100644
--- a/rust/kernel/drm/mod.rs
+++ b/rust/kernel/drm/mod.rs
@@ -8,3 +8,4 @@ pub mod file;
 pub mod gem;
 pub mod ioctl;
 pub mod mm;
+pub mod syncobj;
diff --git a/rust/kernel/drm/syncobj.rs b/rust/kernel/drm/syncobj.rs
new file mode 100644
index 000000000000..10eed05eb27a
--- /dev/null
+++ b/rust/kernel/drm/syncobj.rs
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+//! DRM Sync Objects
+//!
+//! C header: [`include/linux/drm/drm_syncobj.h`](../../../../include/linux/drm/drm_syncobj.h)
+
+use crate::{bindings, dma_fence::*, drm, error::Result, prelude::*};
+
+/// A DRM Sync Object
+///
+/// # Invariants
+/// ptr is a valid pointer to a drm_syncobj and we own a reference to it.
+pub struct SyncObj {
+    ptr: *mut bindings::drm_syncobj,
+}
+
+impl SyncObj {
+    /// Looks up a sync object by its handle for a given `File`.
+    pub fn lookup_handle(file: &impl drm::file::GenericFile, handle: u32) -> Result<SyncObj> {
+        // SAFETY: The arguments are all valid per the type invariants.
+        let ptr = unsafe { bindings::drm_syncobj_find(file.raw() as *mut _, handle) };
+
+        if ptr.is_null() {
+            Err(ENOENT)
+        } else {
+            Ok(SyncObj { ptr })
+        }
+    }
+
+    /// Returns the DMA fence associated with this sync object, if any.
+    pub fn fence_get(&self) -> Option<Fence> {
+        let fence = unsafe { bindings::drm_syncobj_fence_get(self.ptr) };
+        if fence.is_null() {
+            None
+        } else {
+            // SAFETY: The pointer is non-NULL and drm_syncobj_fence_get acquired an
+            // additional reference.
+            Some(unsafe { Fence::from_raw(fence) })
+        }
+    }
+
+    /// Replaces the DMA fence with a new one, or removes it if fence is None.
+    pub fn replace_fence(&self, fence: Option<&Fence>) {
+        unsafe {
+            bindings::drm_syncobj_replace_fence(
+                self.ptr,
+                fence.map_or(core::ptr::null_mut(), |a| a.raw()),
+            )
+        };
+    }
+
+    /// Adds a new timeline point to the syncobj.
+    pub fn add_point(&self, chain: FenceChain, fence: &Fence, point: u64) {
+        // SAFETY: All arguments should be valid per the respective type invariants.
+        // This takes over the FenceChain ownership.
+        unsafe { bindings::drm_syncobj_add_point(self.ptr, chain.into_raw(), fence.raw(), point) };
+    }
+}
+
+impl Drop for SyncObj {
+    fn drop(&mut self) {
+        // SAFETY: We own a reference to this syncobj.
+        unsafe { bindings::drm_syncobj_put(self.ptr) };
+    }
+}
+
+impl Clone for SyncObj {
+    fn clone(&self) -> Self {
+        // SAFETY: `ptr` is valid per the type invariant and we own a reference to it.
+        unsafe { bindings::drm_syncobj_get(self.ptr) };
+        SyncObj { ptr: self.ptr }
+    }
+}
+
+// SAFETY: drm_syncobj operations are internally locked.
+unsafe impl Sync for SyncObj {}
+unsafe impl Send for SyncObj {}

-- 
2.35.1