rust: drm: gem: shmem: Add DRM shmem helper abstraction

The DRM shmem helper includes common code useful for drivers which
allocate GEM objects as anonymous shmem. Add a Rust abstraction for
this. Drivers can choose the raw GEM implementation or the shmem layer,
depending on their needs.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

rust/bindings/bindings_helper.h

@@ -10,6 +10,7 @@
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
 #include <drm/drm_gem.h>
+#include <drm/drm_gem_shmem_helper.h>
 #include <drm/drm_ioctl.h>
 #include <linux/delay.h>
 #include <linux/device.h>
@@ -18,6 +19,7 @@
 #include <linux/slab.h>
 #include <linux/fs.h>
 #include <linux/io-pgtable.h>
+#include <linux/iosys-map.h>
 #include <linux/ktime.h>
 #include <linux/lockdep.h>
 #include <linux/of.h>

rust/helpers.c

@@ -19,6 +19,7 @@
  */
 
 #include <drm/drm_gem.h>
+#include <drm/drm_gem_shmem_helper.h>
 #include <linux/bug.h>
 #include <linux/build_bug.h>
 #include <linux/device.h>
@@ -423,6 +424,18 @@ resource_size_t rust_helper_resource_size(const struct resource *res)
 }
 EXPORT_SYMBOL_GPL(rust_helper_resource_size);
 
+dma_addr_t rust_helper_sg_dma_address(const struct scatterlist *sg)
+{
+	return sg_dma_address(sg);
+}
+EXPORT_SYMBOL_GPL(rust_helper_sg_dma_address);
+
+int rust_helper_sg_dma_len(const struct scatterlist *sg)
+{
+	return sg_dma_len(sg);
+}
+EXPORT_SYMBOL_GPL(rust_helper_sg_dma_len);
+
 #ifdef CONFIG_DRM
 
 void rust_helper_drm_gem_object_get(struct drm_gem_object *obj)
@@ -443,6 +456,60 @@ __u64 rust_helper_drm_vma_node_offset_addr(struct drm_vma_offset_node *node)
 }
 EXPORT_SYMBOL_GPL(rust_helper_drm_vma_node_offset_addr);
 
+#ifdef CONFIG_DRM_GEM_SHMEM_HELPER
+
+void rust_helper_drm_gem_shmem_object_free(struct drm_gem_object *obj)
+{
+	return drm_gem_shmem_object_free(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_free);
+
+void rust_helper_drm_gem_shmem_object_print_info(struct drm_printer *p, unsigned int indent,
+						   const struct drm_gem_object *obj)
+{
+	drm_gem_shmem_object_print_info(p, indent, obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_print_info);
+
+int rust_helper_drm_gem_shmem_object_pin(struct drm_gem_object *obj)
+{
+	return drm_gem_shmem_object_pin(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_pin);
+
+void rust_helper_drm_gem_shmem_object_unpin(struct drm_gem_object *obj)
+{
+	drm_gem_shmem_object_unpin(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_unpin);
+
+struct sg_table *rust_helper_drm_gem_shmem_object_get_sg_table(struct drm_gem_object *obj)
+{
+	return drm_gem_shmem_object_get_sg_table(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_get_sg_table);
+
+int rust_helper_drm_gem_shmem_object_vmap(struct drm_gem_object *obj,
+					    struct iosys_map *map)
+{
+	return drm_gem_shmem_object_vmap(obj, map);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_vmap);
+
+void rust_helper_drm_gem_shmem_object_vunmap(struct drm_gem_object *obj,
+					       struct iosys_map *map)
+{
+	drm_gem_shmem_object_vunmap(obj, map);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_vunmap);
+
+int rust_helper_drm_gem_shmem_object_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
+{
+	return drm_gem_shmem_object_mmap(obj, vma);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_mmap);
+
+#endif
 #endif
 
 /*

rust/kernel/drm/gem/mod.rs

@@ -4,6 +4,9 @@
 //!
 //! C header: [`include/linux/drm/drm_gem.h`](../../../../include/linux/drm/drm_gem.h)
 
+#[cfg(CONFIG_DRM_GEM_SHMEM_HELPER = "y")]
+pub mod shmem;
+
 use alloc::boxed::Box;
 
 use crate::{
@@ -195,8 +198,6 @@ impl<T: IntoGEMObject> BaseObject for T {}
 #[pin_data]
 pub struct Object<T: DriverObject> {
     obj: bindings::drm_gem_object,
-    // The DRM core ensures the Device exists as long as its objects exist, so we don't need to
-    // manage the reference count here.
     dev: *const bindings::drm_device,
     #[pin]
     inner: T,
@@ -236,14 +237,12 @@ impl<T: DriverObject> Object<T> {
                 ..Default::default()
             },
             inner <- T::new(dev, size),
-            // SAFETY: The drm subsystem guarantees that the drm_device will live as long as
-            // the GEM object lives, so we can conjure a reference out of thin air.
             dev: dev.drm.get(),
             _p: PhantomPinned
         }))?;
 
         to_result(unsafe {
-            bindings::drm_gem_object_init(dev.raw() as *mut _, &obj.obj as *const _ as *mut _, size)
+            bindings::drm_gem_object_init(dev.raw_mut(), &obj.obj as *const _ as *mut _, size)
         })?;
 
         // SAFETY: We never move out of self