[PATCH 1/8] rust: io: generalize `MmioRaw` to pointer to arbitrary type

[Gary Guo <gary@kernel.org>]

From: Gary Guo <gary@garyguo.net>

Conceptually, `MmioRaw` is just `__iomem *`, so it should work for any
types. The existing use case where it represents a region of compile-time
known minimum size and run-time known actual size is moved to a custom
dynamic-sized type `Region<SIZE>` instead. The `maxsize` method is also
renamed to `size` to reflect that it is the actual size (not a bound) of
the region.

Signed-off-by: Gary Guo <gary@garyguo.net>
---
 rust/kernel/devres.rs |  7 ++--
 rust/kernel/io.rs     | 84 +++++++++++++++++++++++++++++++++----------
 rust/kernel/io/mem.rs |  4 +--
 rust/kernel/pci/io.rs |  4 +--
 4 files changed, 74 insertions(+), 25 deletions(-)

diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index 9e5f93aed20c..65a4082122af 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -71,14 +71,15 @@ struct Inner<T> {
 ///         IoKnownSize,
 ///         Mmio,
 ///         MmioRaw,
-///         PhysAddr, //
+///         PhysAddr,
+///         Region, //
 ///     },
 ///     prelude::*,
 /// };
 /// use core::ops::Deref;
 ///
 /// // See also [`pci::Bar`] for a real example.
-/// struct IoMem<const SIZE: usize>(MmioRaw<SIZE>);
+/// struct IoMem<const SIZE: usize>(MmioRaw<Region<SIZE>>);
 ///
 /// impl<const SIZE: usize> IoMem<SIZE> {
 ///     /// # Safety
@@ -93,7 +94,7 @@ struct Inner<T> {
 ///             return Err(ENOMEM);
 ///         }
 ///
-///         Ok(IoMem(MmioRaw::new(addr as usize, SIZE)?))
+///         Ok(IoMem(MmioRaw::new_region(addr as usize, SIZE)?))
 ///     }
 /// }
 ///
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index fcc7678fd9e3..d7f2145fa9b9 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -6,7 +6,8 @@
 
 use crate::{
     bindings,
-    prelude::*, //
+    prelude::*,
+    ptr::KnownSize, //
 };
 
 pub mod mem;
@@ -31,39 +32,85 @@
 /// `CONFIG_PHYS_ADDR_T_64BIT`, and it can be a u64 even on 32-bit architectures.
 pub type ResourceSize = bindings::resource_size_t;
 
+/// Untyped I/O region.
+///
+/// This type can be used when an I/O region without known type information has a compile-time known
+/// minimum size (and a runtime known actual size).
+///
+/// The `SIZE` generic parameter indicate the minimum size of the region.
+#[repr(transparent)]
+pub struct Region<const SIZE: usize = 0> {
+    inner: [u8],
+}
+
+impl<const SIZE: usize> KnownSize for Region<SIZE> {
+    #[inline(always)]
+    fn size(p: *const Self) -> usize {
+        (p as *const [u8]).len()
+    }
+}
+
 /// Raw representation of an MMIO region.
 ///
+/// `MmioRaw<T>` is equivalent to `T __iomem *` in C.
+///
 /// By itself, the existence of an instance of this structure does not provide any guarantees that
 /// the represented MMIO region does exist or is properly mapped.
 ///
 /// Instead, the bus specific MMIO implementation must convert this raw representation into an
 /// `Mmio` instance providing the actual memory accessors. Only by the conversion into an `Mmio`
 /// structure any guarantees are given.
-pub struct MmioRaw<const SIZE: usize = 0> {
-    addr: usize,
-    maxsize: usize,
+pub struct MmioRaw<T: ?Sized> {
+    /// Pointer is in I/O address space.
+    ///
+    /// The provenance does not matter, only the address and metadata do.
+    addr: *mut T,
 }
 
-impl<const SIZE: usize> MmioRaw<SIZE> {
-    /// Returns a new `MmioRaw` instance on success, an error otherwise.
-    pub fn new(addr: usize, maxsize: usize) -> Result<Self> {
-        if maxsize < SIZE {
+// SAFETY: `MmioRaw` is just an address, so is thread-safe.
+unsafe impl<T: ?Sized> Send for MmioRaw<T> {}
+// SAFETY: `MmioRaw` is just an address, so is thread-safe.
+unsafe impl<T: ?Sized> Sync for MmioRaw<T> {}
+
+impl<T> MmioRaw<T> {
+    /// Create a `MmioRaw` from address.
+    #[inline]
+    pub fn new(addr: usize) -> Self {
+        Self {
+            addr: core::ptr::without_provenance_mut(addr),
+        }
+    }
+}
+
+impl<const SIZE: usize> MmioRaw<Region<SIZE>> {
+    /// Create a `MmioRaw` representing a I/O region with given size.
+    ///
+    /// The size is checked against the minimum size specified via const generics.
+    #[inline]
+    pub fn new_region(addr: usize, size: usize) -> Result<Self> {
+        if size < SIZE {
             return Err(EINVAL);
         }
 
-        Ok(Self { addr, maxsize })
+        let addr = core::ptr::slice_from_raw_parts_mut::<u8>(
+            core::ptr::without_provenance_mut(addr),
+            size,
+        ) as *mut Region<SIZE>;
+        Ok(Self { addr })
     }
+}
 
+impl<T: ?Sized + KnownSize> MmioRaw<T> {
     /// Returns the base address of the MMIO region.
     #[inline]
     pub fn addr(&self) -> usize {
-        self.addr
+        self.addr.addr()
     }
 
-    /// Returns the maximum size of the MMIO region.
+    /// Returns the size of the MMIO region.
     #[inline]
-    pub fn maxsize(&self) -> usize {
-        self.maxsize
+    pub fn size(&self) -> usize {
+        KnownSize::size(self.addr)
     }
 }
 
@@ -89,12 +136,13 @@ pub fn maxsize(&self) -> usize {
 ///         Mmio,
 ///         MmioRaw,
 ///         PhysAddr,
+///         Region,
 ///     },
 /// };
 /// use core::ops::Deref;
 ///
 /// // See also `pci::Bar` for a real example.
-/// struct IoMem<const SIZE: usize>(MmioRaw<SIZE>);
+/// struct IoMem<const SIZE: usize>(MmioRaw<Region<SIZE>>);
 ///
 /// impl<const SIZE: usize> IoMem<SIZE> {
 ///     /// # Safety
@@ -109,7 +157,7 @@ pub fn maxsize(&self) -> usize {
 ///             return Err(ENOMEM);
 ///         }
 ///
-///         Ok(IoMem(MmioRaw::new(addr as usize, SIZE)?))
+///         Ok(IoMem(MmioRaw::new_region(addr as usize, SIZE)?))
 ///     }
 /// }
 ///
@@ -139,7 +187,7 @@ pub fn maxsize(&self) -> usize {
 /// # }
 /// ```
 #[repr(transparent)]
-pub struct Mmio<const SIZE: usize = 0>(MmioRaw<SIZE>);
+pub struct Mmio<const SIZE: usize = 0>(MmioRaw<Region<SIZE>>);
 
 /// Checks whether an access of type `U` at the given `offset`
 /// is valid within this region.
@@ -767,7 +815,7 @@ fn addr(&self) -> usize {
     /// Returns the maximum size of this mapping.
     #[inline]
     fn maxsize(&self) -> usize {
-        self.0.maxsize()
+        self.0.size()
     }
 }
 
@@ -782,7 +830,7 @@ impl<const SIZE: usize> Mmio<SIZE> {
     ///
     /// Callers must ensure that `addr` is the start of a valid I/O mapped memory region of size
     /// `maxsize`.
-    pub unsafe fn from_raw(raw: &MmioRaw<SIZE>) -> &Self {
+    pub unsafe fn from_raw(raw: &MmioRaw<Region<SIZE>>) -> &Self {
         // SAFETY: `Mmio` is a transparent wrapper around `MmioRaw`.
         unsafe { &*core::ptr::from_ref(raw).cast() }
     }
diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
index 7dc78d547f7a..9117d417f99c 100644
--- a/rust/kernel/io/mem.rs
+++ b/rust/kernel/io/mem.rs
@@ -231,7 +231,7 @@ fn deref(&self) -> &Self::Target {
 /// [`IoMem`] always holds an [`MmioRaw`] instance that holds a valid pointer to the
 /// start of the I/O memory mapped region.
 pub struct IoMem<const SIZE: usize = 0> {
-    io: MmioRaw<SIZE>,
+    io: MmioRaw<super::Region<SIZE>>,
 }
 
 impl<const SIZE: usize> IoMem<SIZE> {
@@ -266,7 +266,7 @@ fn ioremap(resource: &Resource) -> Result<Self> {
             return Err(ENOMEM);
         }
 
-        let io = MmioRaw::new(addr as usize, size)?;
+        let io = MmioRaw::new_region(addr as usize, size)?;
         let io = IoMem { io };
 
         Ok(io)
diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
index ae78676c927f..0335b5068f69 100644
--- a/rust/kernel/pci/io.rs
+++ b/rust/kernel/pci/io.rs
@@ -148,7 +148,7 @@ impl<'a, S: ConfigSpaceKind> IoKnownSize for ConfigSpace<'a, S> {
 /// memory mapped PCI BAR and its size.
 pub struct Bar<const SIZE: usize = 0> {
     pdev: ARef<Device>,
-    io: MmioRaw<SIZE>,
+    io: MmioRaw<crate::io::Region<SIZE>>,
     num: i32,
 }
 
@@ -184,7 +184,7 @@ pub(super) fn new(pdev: &Device, num: u32, name: &CStr) -> Result<Self> {
             return Err(ENOMEM);
         }
 
-        let io = match MmioRaw::new(ioptr, len as usize) {
+        let io = match MmioRaw::new_region(ioptr, len as usize) {
             Ok(io) => io,
             Err(err) => {
                 // SAFETY:
-- 
2.51.2