rust: io: add resource abstraction

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.

Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Co-developed-by: Fiona Behrens <me@kloenk.dev>
Signed-off-by: Fiona Behrens <me@kloenk.dev>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250717-topics-tyr-platform_iomem-v15-1-beca780b77e3@collabora.com
[ Capitalize safety comments and end it with a period. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/bindings/bindings_helper.h

@@ -53,6 +53,7 @@
 #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>

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 +100,38 @@ void rust_helper_writeq_relaxed(u64 value, void __iomem *addr)
 	writeq_relaxed(value, addr);
 }
 #endif
+
+resource_size_t rust_helper_resource_size(struct resource *res)
+{
+	return resource_size(res);
+}
+
+struct resource *rust_helper_request_mem_region(resource_size_t start,
+						resource_size_t n,
+						const char *name)
+{
+	return request_mem_region(start, n, name);
+}
+
+void rust_helper_release_mem_region(resource_size_t start, resource_size_t n)
+{
+	release_mem_region(start, n);
+}
+
+struct resource *rust_helper_request_region(resource_size_t start,
+					    resource_size_t n, const char *name)
+{
+	return request_region(start, n, name);
+}
+
+struct resource *rust_helper_request_muxed_region(resource_size_t start,
+						  resource_size_t n,
+						  const char *name)
+{
+	return request_muxed_region(start, n, name);
+}
+
+void rust_helper_release_region(resource_size_t start, resource_size_t n)
+{
+	release_region(start, n);
+}

rust/kernel/io.rs

@@ -7,6 +7,10 @@
 use crate::error::{code::EINVAL, Result};
 use crate::{bindings, build_assert};
 
+pub mod resource;
+
+pub use resource::Resource;
+
 /// Raw representation of an MMIO region.
 ///
 /// By itself, the existence of an instance of this structure does not provide any guarantees that

rust/kernel/io/resource.rs

@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Abstractions for [system
+//! resources](https://docs.kernel.org/core-api/kernel-api.html#resources-management).
+//!
+//! C header: [`include/linux/ioport.h`](srctree/include/linux/ioport.h)
+
+use core::ops::Deref;
+use core::ptr::NonNull;
+
+use crate::prelude::*;
+use crate::str::{CStr, CString};
+use crate::types::Opaque;
+
+/// Resource Size type.
+///
+/// This is a type alias to either `u32` or `u64` depending on the config option
+/// `CONFIG_PHYS_ADDR_T_64BIT`, and it can be a u64 even on 32-bit architectures.
+pub type ResourceSize = bindings::phys_addr_t;
+
+/// A region allocated from a parent [`Resource`].
+///
+/// # Invariants
+///
+/// - `self.0` points to a valid `bindings::resource` that was obtained through
+///   `bindings::__request_region`.
+pub struct Region {
+    /// The resource returned when the region was requested.
+    resource: NonNull<bindings::resource>,
+    /// The name that was passed in when the region was requested. We need to
+    /// store it for ownership reasons.
+    _name: CString,
+}
+
+impl Deref for Region {
+    type Target = Resource;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: Safe as per the invariant of `Region`.
+        unsafe { Resource::from_raw(self.resource.as_ptr()) }
+    }
+}
+
+impl Drop for Region {
+    fn drop(&mut self) {
+        let (flags, start, size) = {
+            let res = &**self;
+            (res.flags(), res.start(), res.size())
+        };
+
+        let release_fn = if flags.contains(Flags::IORESOURCE_MEM) {
+            bindings::release_mem_region
+        } else {
+            bindings::release_region
+        };
+
+        // SAFETY: Safe as per the invariant of `Region`.
+        unsafe { release_fn(start, size) };
+    }
+}
+
+// SAFETY: `Region` only holds a pointer to a C `struct resource`, which is safe to be used from
+// any thread.
+unsafe impl Send for Region {}
+
+// SAFETY: `Region` only holds a pointer to a C `struct resource`, references to which are
+// safe to be used from any thread.
+unsafe impl Sync for Region {}
+
+/// A resource abstraction.
+///
+/// # Invariants
+///
+/// [`Resource`] is a transparent wrapper around a valid `bindings::resource`.
+#[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) const unsafe fn from_raw<'a>(ptr: *mut bindings::resource) -> &'a Self {
+        // SAFETY: Self is a transparent wrapper around `Opaque<bindings::resource>`.
+        unsafe { &*ptr.cast() }
+    }
+
+    /// Requests a resource region.
+    ///
+    /// Exclusive access will be given and the region will be marked as busy.
+    /// Further calls to [`Self::request_region`] will return [`None`] if
+    /// the region, or a part of it, is already in use.
+    pub fn request_region(
+        &self,
+        start: ResourceSize,
+        size: ResourceSize,
+        name: CString,
+        flags: Flags,
+    ) -> Option<Region> {
+        // SAFETY:
+        // - Safe as per the invariant of `Resource`.
+        // - `__request_region` will store a reference to the name, but that is
+        // safe as we own it and it will not be dropped until the `Region` is
+        // dropped.
+        let region = unsafe {
+            bindings::__request_region(
+                self.0.get(),
+                start,
+                size,
+                name.as_char_ptr(),
+                flags.0 as c_int,
+            )
+        };
+
+        Some(Region {
+            resource: NonNull::new(region)?,
+            _name: name,
+        })
+    }
+
+    /// Returns the size of the resource.
+    pub fn size(&self) -> ResourceSize {
+        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) -> ResourceSize {
+        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) -> Option<&CStr> {
+        let inner = self.0.get();
+
+        // SAFETY: Safe as per the invariants of `Resource`.
+        let name = unsafe { (*inner).name };
+
+        if name.is_null() {
+            return None;
+        }
+
+        // SAFETY: In the C code, `resource::name` either contains a null
+        // pointer or points to a valid NUL-terminated C string, and at this
+        // point we know it is not null, so we can safely convert it to a
+        // `CStr`.
+        Some(unsafe { CStr::from_char_ptr(name) })
+    }
+
+    /// Returns the flags associated with the resource.
+    pub fn flags(&self) -> Flags {
+        let inner = self.0.get();
+        // SAFETY: Safe as per the invariants of `Resource`.
+        let flags = unsafe { (*inner).flags };
+
+        Flags(flags)
+    }
+}
+
+// SAFETY: `Resource` only holds a pointer to a C `struct resource`, which is
+// safe to be used from any thread.
+unsafe impl Send for Resource {}
+
+// SAFETY: `Resource` only holds a pointer to a C `struct resource`, references
+// to which are safe to be used from any thread.
+unsafe impl Sync for Resource {}
+
+/// Resource flags as stored in the C `struct resource::flags` field.
+///
+/// They can be combined with the operators `|`, `&`, and `!`.
+///
+/// Values can be used from the [`flags`] module.
+#[derive(Clone, Copy, PartialEq)]
+pub struct Flags(c_ulong);
+
+impl Flags {
+    /// Check whether `flags` is contained in `self`.
+    pub fn contains(self, flags: Flags) -> bool {
+        (self & flags) == flags
+    }
+}
+
+impl core::ops::BitOr for Flags {
+    type Output = Self;
+    fn bitor(self, rhs: Self) -> Self::Output {
+        Self(self.0 | rhs.0)
+    }
+}
+
+impl core::ops::BitAnd for Flags {
+    type Output = Self;
+    fn bitand(self, rhs: Self) -> Self::Output {
+        Self(self.0 & rhs.0)
+    }
+}
+
+impl core::ops::Not for Flags {
+    type Output = Self;
+    fn not(self) -> Self::Output {
+        Self(!self.0)
+    }
+}
+
+impl Flags {
+    /// PCI/ISA I/O ports.
+    pub const IORESOURCE_IO: Flags = Flags::new(bindings::IORESOURCE_IO);
+
+    /// Resource is software muxed.
+    pub const IORESOURCE_MUXED: Flags = Flags::new(bindings::IORESOURCE_MUXED);
+
+    /// Resource represents a memory region.
+    pub const IORESOURCE_MEM: Flags = Flags::new(bindings::IORESOURCE_MEM);
+
+    /// Resource represents a memory region that must be ioremaped using `ioremap_np`.
+    pub const IORESOURCE_MEM_NONPOSTED: Flags = Flags::new(bindings::IORESOURCE_MEM_NONPOSTED);
+
+    const fn new(value: u32) -> Self {
+        crate::build_assert!(value as u64 <= c_ulong::MAX as u64);
+        Flags(value as c_ulong)
+    }
+}