rust: io: always inline functions using build_assert with arguments

`build_assert` relies on the compiler to optimize out its error path.
Functions using it with its arguments must thus always be inlined,
otherwise the error path of `build_assert` might not be optimized out,
triggering a build error.

Cc: stable@vger.kernel.org
Fixes: ce30d94 ("rust: add `io::{Io, IoRaw}` base types")
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Timur Tabi <ttabi@nvidia.com>
Link: https://patch.msgid.link/20251208-io-build-assert-v3-2-98aded02c1ea@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: Gnurou

rust/kernel/io.rs

@@ -142,7 +142,8 @@ macro_rules! define_read {
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
         /// time, the build will fail.
         $(#[$attr])*
-        #[inline]
+        // Always inline to optimize out error path of `io_addr_assert`.
+        #[inline(always)]
         pub fn $name(&self, offset: usize) -> $type_name {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
@@ -171,7 +172,8 @@ macro_rules! define_write {
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
         /// time, the build will fail.
         $(#[$attr])*
-        #[inline]
+        // Always inline to optimize out error path of `io_addr_assert`.
+        #[inline(always)]
         pub fn $name(&self, value: $type_name, offset: usize) {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
@@ -239,7 +241,8 @@ impl<const SIZE: usize> Io<SIZE> {
         self.addr().checked_add(offset).ok_or(EINVAL)
     }
 
-    #[inline]
+    // Always inline to optimize out error path of `build_assert`.
+    #[inline(always)]
     fn io_addr_assert<U>(&self, offset: usize) -> usize {
         build_assert!(Self::offset_valid::<U>(offset, SIZE));
 

rust/kernel/io/resource.rs

@@ -226,6 +226,8 @@ impl Flags {
     /// Resource represents a memory region that must be ioremaped using `ioremap_np`.
     pub const IORESOURCE_MEM_NONPOSTED: Flags = Flags::new(bindings::IORESOURCE_MEM_NONPOSTED);
 
+    // Always inline to optimize out error path of `build_assert`.
+    #[inline(always)]
     const fn new(value: u32) -> Self {
         crate::build_assert!(value as u64 <= c_ulong::MAX as u64);
         Flags(value as c_ulong)