rust: helpers: Add dma_alloc_attrs() and dma_free_attrs()

Add dma_alloc_attrs() and dma_free_attrs() helpers to fix a build
error when CONFIG_HAS_DMA is not enabled.

Note that when CONFIG_HAS_DMA is enabled, dma_alloc_attrs() and
dma_free_attrs() are included in both bindings_generated.rs and
bindings_helpers_generated.rs. The former takes precedence so behavior
remains unchanged in that case.

This fixes the following build error on UML:

error[E0425]: cannot find function `dma_alloc_attrs` in crate `bindings`
     --> rust/kernel/dma.rs:171:23
      |
171   |               bindings::dma_alloc_attrs(
      |                         ^^^^^^^^^^^^^^^ help: a function with a similar name exists: `dma_alloc_pages`
      |
     ::: rust/bindings/bindings_generated.rs:44568:5
      |
44568 | /     pub fn dma_alloc_pages(
44569 | |         dev: *mut device,
44570 | |         size: usize,
44571 | |         dma_handle: *mut dma_addr_t,
44572 | |         dir: dma_data_direction,
44573 | |         gfp: gfp_t,
44574 | |     ) -> *mut page;
      | |___________________- similarly named function `dma_alloc_pages` defined here

error[E0425]: cannot find function `dma_free_attrs` in crate `bindings`
     --> rust/kernel/dma.rs:293:23
      |
293   |               bindings::dma_free_attrs(
      |                         ^^^^^^^^^^^^^^ help: a function with a similar name exists: `dma_free_pages`
      |
     ::: rust/bindings/bindings_generated.rs:44577:5
      |
44577 | /     pub fn dma_free_pages(
44578 | |         dev: *mut device,
44579 | |         size: usize,
44580 | |         page: *mut page,
44581 | |         dma_handle: dma_addr_t,
44582 | |         dir: dma_data_direction,
44583 | |     );
      | |______- similarly named function `dma_free_pages` defined here

Fixes: ad2907b ("rust: add dma coherent allocator abstraction")
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250412000507.157000-1-fujita.tomonori@gmail.com
[ Reworded for relative paths. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

MAINTAINERS

@@ -7020,6 +7020,7 @@ L:	rust-for-linux@vger.kernel.org
 S:	Supported
 W:	https://rust-for-linux.com
 T:	git https://github.com/Rust-for-Linux/linux.git alloc-next
+F:	rust/helpers/dma.c
 F:	rust/kernel/dma.rs
 F:	samples/rust/rust_dma.rs
 

rust/helpers/dma.c

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/dma-mapping.h>
+
+void *rust_helper_dma_alloc_attrs(struct device *dev, size_t size,
+				  dma_addr_t *dma_handle, gfp_t flag,
+				  unsigned long attrs)
+{
+	return dma_alloc_attrs(dev, size, dma_handle, flag, attrs);
+}
+
+void rust_helper_dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
+				dma_addr_t dma_handle, unsigned long attrs)
+{
+	dma_free_attrs(dev, size, cpu_addr, dma_handle, attrs);
+}

rust/helpers/helpers.c

@@ -14,6 +14,7 @@
 #include "cpumask.c"
 #include "cred.c"
 #include "device.c"
+#include "dma.c"
 #include "err.c"
 #include "fs.c"
 #include "io.c"