[PATCH 1/2] rust: io: gate ioremap/iounmap on CONFIG_HAS_IOMEM

[Danilo Krummrich <dakr@kernel.org>]

s390 does not provide ioremap()/iounmap() when CONFIG_HAS_IOMEM is not
set (which requires CONFIG_PCI on that architecture). This causes a
build failure with Rust enabled on e.g. s390 allnoconfig:

	In file included from rust/helpers/helpers.c:68:
	rust/helpers/io.c:8:9: error: call to undeclared function 'ioremap'; ISO C99 and later do not support implicit function declarations
	      [-Wimplicit-function-declaration]
	    8 |         return ioremap(offset, size);
	      |                ^
	rust/helpers/io.c:19:2: error: call to undeclared function 'iounmap'; ISO C99 and later do not support implicit function declarations
	      [-Wimplicit-function-declaration]
	   19 |         iounmap(addr);

Guard the C helpers behind #ifdef CONFIG_HAS_IOMEM and provide a
cfg-gated stub in IoMem::ioremap() that returns -EINVAL when IOMEM is
unavailable, mirroring the C pattern used by
devm_platform_ioremap_resource() and friends.

Reported-by: Miguel Ojeda <ojeda@kernel.org>
Closes: https://lore.kernel.org/all/20260803180931.97202-1-ojeda@kernel.org
Fixes: 3f70ebe63858 ("s390: Enable Rust support")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/helpers/io.c     |  2 ++
 rust/kernel/io/mem.rs | 11 ++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/rust/helpers/io.c b/rust/helpers/io.c
index 397810864a24..1edbc274951c 100644
--- a/rust/helpers/io.c
+++ b/rust/helpers/io.c
@@ -3,6 +3,7 @@
 #include <linux/io.h>
 #include <linux/ioport.h>
 
+#ifdef CONFIG_HAS_IOMEM
 __rust_helper void __iomem *rust_helper_ioremap(phys_addr_t offset, size_t size)
 {
 	return ioremap(offset, size);
@@ -18,6 +19,7 @@ __rust_helper void rust_helper_iounmap(void __iomem *addr)
 {
 	iounmap(addr);
 }
+#endif /* CONFIG_HAS_IOMEM */
 
 __rust_helper u8 rust_helper_readb(const void __iomem *addr)
 {
diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
index fc2a3e24f8d5..3f596bc4fb26 100644
--- a/rust/kernel/io/mem.rs
+++ b/rust/kernel/io/mem.rs
@@ -233,6 +233,12 @@ pub struct IoMem<'a, const SIZE: usize = 0> {
 }
 
 impl<'a, const SIZE: usize> IoMem<'a, SIZE> {
+    #[cfg(not(CONFIG_HAS_IOMEM))]
+    fn ioremap(_dev: &'a Device<Bound>, _resource: &Resource) -> Result<Self> {
+        Err(EINVAL)
+    }
+
+    #[cfg(CONFIG_HAS_IOMEM)]
     fn ioremap(dev: &'a Device<Bound>, resource: &Resource) -> Result<Self> {
         // Note: Some ioremap() implementations use types that depend on the CPU
         // word width rather than the bus address width.
@@ -286,8 +292,11 @@ pub fn into_devres(self) -> Result<Devres<IoMem<'static, SIZE>>> {
 
 impl<const SIZE: usize> Drop for IoMem<'_, SIZE> {
     fn drop(&mut self) {
+        #[cfg(CONFIG_HAS_IOMEM)]
         // SAFETY: Safe as by the invariant of `Io`.
-        unsafe { bindings::iounmap(self.io.addr() as *mut c_void) }
+        unsafe {
+            bindings::iounmap(self.io.addr() as *mut c_void)
+        }
     }
 }
 

base-commit: 667d0fb32149f023b8b34a1f6f3d384556eafb5a
-- 
2.55.0