[PATCH] rust: io: fix Mmio::from_raw safety docs

[Yilin Chen]

MmioRaw can be constructed safely. It also explicitly does not guarantee
that the represented MMIO range exists or is mapped.

The unsafe precondition for Mmio::from_raw() therefore belongs to the
range described by the MmioRaw argument, not to nonexistent addr and
maxsize parameters. Document that this range must stay valid for the
returned reference.

Assisted-by: Codex:GPT-5
Signed-off-by: Yilin Chen <1479826151@xxxxxx>
---
 rust/kernel/io.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index fcc7678fd..59b276a04 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -780,8 +780,9 @@ impl<const SIZE: usize> Mmio<SIZE> {
     ///
     /// # Safety
     ///
-    /// Callers must ensure that `addr` is the start of a valid I/O mapped memory region of size
-    /// `maxsize`.
+    /// Callers must ensure that the MMIO range described by `raw.addr()` and
+    /// `raw.maxsize()` is a valid I/O mapped memory region for the entire lifetime
+    /// of the returned reference.
     pub unsafe fn from_raw(raw: &MmioRaw<SIZE>) -> &Self {
         // SAFETY: `Mmio` is a transparent wrapper around `MmioRaw`.
         unsafe { &*core::ptr::from_ref(raw).cast() }
-- 
2.25.1