[PATCH v4 1/3] rust: io: add resource abstraction

[Daniel Almeida <daniel.almeida@collabora.com>]

In preparation for ioremap support, add a Rust abstraction for struct
resource.

A future commit will introduce the Rust API to ioremap a resource from a
platform device. The current abstraction, therefore, adds only the
minimum API needed to get that done.

Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
---
 rust/bindings/bindings_helper.h |  1 +
 rust/helpers/io.c               |  7 +++++
 rust/kernel/io.rs               |  2 ++
 rust/kernel/io/resource.rs      | 49 +++++++++++++++++++++++++++++++++
 4 files changed, 59 insertions(+)
 create mode 100644 rust/kernel/io/resource.rs

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index e9fdceb568b8..f9c2eedb5b9b 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -16,6 +16,7 @@
 #include <linux/file.h>
 #include <linux/firmware.h>
 #include <linux/fs.h>
+#include <linux/ioport.h>
 #include <linux/jiffies.h>
 #include <linux/jump_label.h>
 #include <linux/mdio.h>
diff --git a/rust/helpers/io.c b/rust/helpers/io.c
index 4c2401ccd720..3cb47bd01942 100644
--- a/rust/helpers/io.c
+++ b/rust/helpers/io.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/io.h>
+#include <linux/ioport.h>
 
 void __iomem *rust_helper_ioremap(phys_addr_t offset, size_t size)
 {
@@ -99,3 +100,9 @@ void rust_helper_writeq_relaxed(u64 value, volatile void __iomem *addr)
 	writeq_relaxed(value, addr);
 }
 #endif
+
+resource_size_t rust_helper_resource_size(struct resource *res)
+{
+	return resource_size(res);
+}
+
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index d4a73e52e3ee..566d8b177e01 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -7,6 +7,8 @@
 use crate::error::{code::EINVAL, Result};
 use crate::{bindings, build_assert};
 
+pub mod resource;
+
 /// Raw representation of an MMIO region.
 ///
 /// By itself, the existence of an instance of this structure does not provide any guarantees that
diff --git a/rust/kernel/io/resource.rs b/rust/kernel/io/resource.rs
new file mode 100644
index 000000000000..84876af1699c
--- /dev/null
+++ b/rust/kernel/io/resource.rs
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Abstraction for system resources.
+//!
+//! C header: [`include/linux/ioport.h`](../../../../include/linux/ioport.h)
+
+use crate::str::CStr;
+use crate::types::Opaque;
+
+/// A resource abstraction.
+#[repr(transparent)]
+pub struct Resource(Opaque<bindings::resource>);
+
+impl Resource {
+    /// Creates a reference to a [`Resource`] from a valid pointer.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that for the duration of 'a, the pointer will
+    /// point at a valid `bindings::resource`
+    ///
+    /// The caller must also ensure that the `Resource` is only accessed via the
+    /// returned reference for the duration of 'a.
+    pub(crate) unsafe fn from_ptr<'a>(ptr: *mut bindings::resource) -> &'a Self {
+        // SAFETY: Self is a transparent wrapper around `Opaque<bindings::resource>`.
+        unsafe { &mut *ptr.cast() }
+    }
+
+    /// Returns the size of the resource.
+    pub fn size(&self) -> bindings::resource_size_t {
+        let inner = self.0.get();
+        // SAFETY: safe as per the invariants of `Resource`
+        unsafe { bindings::resource_size(inner) }
+    }
+
+    /// Returns the start address of the resource.
+    pub fn start(&self) -> u64 {
+        let inner = self.0.get();
+        // SAFETY: safe as per the invariants of `Resource`
+        unsafe { *inner }.start
+    }
+
+    /// Returns the name of the resource.
+    pub fn name(&self) -> &CStr {
+        let inner = self.0.get();
+        // SAFETY: safe as per the invariants of `Resource`
+        unsafe { CStr::from_char_ptr((*inner).name) }
+    }
+}
-- 
2.47.1