Re: [PATCH v5 00/20] rust: I/O type generalization and projection

On Fri Jun 26, 2026 at 4:45 PM CEST, Gary Guo wrote:
> This series presents a major rework of I/O types, as a summary:

There are two minor rustdoc warnings:

	warning: unresolved link to `include/linux/iosys-map.h`
	    --> rust/kernel/io.rs:1456:7
	     |
	1456 | /// [`include/linux/iosys-map.h`] in C.
	     |       ^^^^^^^^^^^^^^^^^^^^^^^^^ no item named `include/linux/iosys-map.h` in scope
	     |
	     = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
	     = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default
	
	warning: unresolved link to `View`
	    --> rust/kernel/io.rs:1620:74
	     |
	1620 | /// In addition to projecting from [`Io`], you may also project from a [`View`] of an [`Io`].
	     |                                                                          ^^^^ no item named `View` in scope
	     |
	     = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
	
	warning: 2 warnings emitted

> Gary Guo (19):
>       rust: io: add dynamically-sized `Region` type
>       rust: io: add missing safety requirement in `IoCapable` methods
>       rust: io: restrict untyped IO access and `register!` to `Region`
>       rust: io: implement `Io` on reference types instead
>       rust: io: generalize `MmioRaw` to pointer to arbitrary type
>       rust: io: rename `Mmio` to `MmioOwned`
>       rust: io: implement `Mmio` as view type
>       rust: pci: io: make `ConfigSpace` a view
>       rust: io: use view types instead of addresses for `Io`
>       pwm: th1520: remove unnecessary `deref`
>       rust: io: remove `MmioOwned`
>       rust: io: move `Io` methods to extension trait
>       rust: io: add projection macro and methods
>       rust: io: implement a view type for `Coherent`
>       rust: io: add `read_val` and `write_val` functions on `Io`
>       gpu: nova-core: use I/O projection for cleaner encapsulation
>       rust: dma: drop `dma_read!` and `dma_write!` API
>       rust: io: add copying methods
>       rust: io: implement `IoSysMap`
>
> Laura Nao (1):
>       rust: io: add I/O backend for system memory with volatile access

For sharing with the drm-rust tree:

diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs
index 3ee19ef6264e..6868b5d80ab7 100644
--- a/rust/kernel/drm/gem/shmem.rs
+++ b/rust/kernel/drm/gem/shmem.rs
@@ -29,9 +29,10 @@
         to_result, //
     },
     io::{
-        Io,
-        IoCapable,
-        IoKnownSize, //
+        IoBase,
+        Region,
+        SysMem,
+        SysMemBackend, //
     },
     prelude::*,
     scatterlist,
@@ -467,6 +468,28 @@ pub fn owner(&self) -> &Object<D, C> {
     }
 }

+impl<'a, D, R, C, const SIZE: usize> IoBase<'a> for &'a VMap<D, R, C, SIZE>
+where
+    D: DriverObject,
+    C: DeviceContext,
+    R: Deref<Target = Object<D, C>>,
+{
+    type Backend = SysMemBackend;
+    type Target = Region<SIZE>;
+
+    #[inline]
+    fn as_view(self) -> SysMem<'a, Region<SIZE>> {
+        let ptr = Region::ptr_from_raw_parts_mut(self.addr.cast(), self.owner.size());
+
+        // SAFETY: Per type invariants of `VMap`:
+        // - `addr .. addr + owner.size()` is a valid kernel accessible memory region.
+        // - `addr` is page-aligned, which satisfies `Region`'s 4-byte alignment requirement.
+        // - The memory remains valid until this `VMap` is dropped; since `self` is `&'a VMap`,
+        //   the borrow prevents the `VMap` from being dropped for the lifetime `'a`.
+        unsafe { SysMem::new(ptr) }
+    }
+}
+
 impl<D, R, C, const SIZE: usize> Drop for VMap<D, R, C, SIZE>
 where
     D: DriverObject,
@@ -508,69 +531,6 @@ unsafe impl<D, R, C, const SIZE: usize> Sync for VMap<D, R, C, SIZE>
 {
 }

-impl<D, R, C, const SIZE: usize> Io for VMap<D, R, C, SIZE>
-where
-    D: DriverObject,
-    C: DeviceContext,
-    R: Deref<Target = Object<D, C>>,
-{
-    #[inline]
-    fn addr(&self) -> usize {
-        self.addr as usize
-    }
-
-    #[inline]
-    fn maxsize(&self) -> usize {
-        self.owner.size()
-    }
-}
-
-impl<D, R, C, const SIZE: usize> IoKnownSize for VMap<D, R, C, SIZE>
-where
-    D: DriverObject,
-    C: DeviceContext,
-    R: Deref<Target = Object<D, C>>,
-{
-    const MIN_SIZE: usize = SIZE;
-}
-
-macro_rules! impl_vmap_io_capable {
-    ($ty:ty) => {
-        impl<D, R, C, const SIZE: usize> IoCapable<$ty> for VMap<D, R, C, SIZE>
-        where
-            D: DriverObject,
-            C: DeviceContext,
-            R: Deref<Target = Object<D, C>>,
-        {
-            #[inline]
-            unsafe fn io_read(&self, address: usize) -> $ty {
-                let ptr = address as *mut $ty;
-
-                // SAFETY: The safety contract of `io_read` guarantees that address is a valid
-                // address within the bounds of `Self` of at least the size of $ty, and is properly
-                // aligned.
-                unsafe { ptr::read_volatile(ptr) }
-            }
-
-            #[inline]
-            unsafe fn io_write(&self, value: $ty, address: usize) {
-                let ptr = address as *mut $ty;
-
-                // SAFETY: The safety contract of `io_write` guarantees that address is a valid
-                // address within the bounds of `Self` of at least the size of $ty, and is properly
-                // aligned.
-                unsafe { ptr::write_volatile(ptr, value) }
-            }
-        }
-    };
-}
-
-impl_vmap_io_capable!(u8);
-impl_vmap_io_capable!(u16);
-impl_vmap_io_capable!(u32);
-#[cfg(CONFIG_64BIT)]
-impl_vmap_io_capable!(u64);
-
 /// A reference to a GEM object that is known to have a mapped [`SGTable`].
 ///
 /// This is used by the Rust bindings with [`Devres`] in order to ensure that mappings for SGTables
@@ -638,6 +598,7 @@ mod tests {
             UnregisteredDevice, //
         },
         faux,
+        io::Io,
         page::PAGE_SIZE, //
     };

@@ -714,7 +675,7 @@ fn compile_time_vmap_sizes() -> Result {
         assert!(ptr::eq(vmap.owner(), obj.deref()));

         // Verify the max size matches the actual object size
-        assert_eq!(vmap.maxsize(), PAGE_SIZE);
+        assert_eq!(vmap.size(), PAGE_SIZE);

         // Make sure creating a vmap that's too large fails
         assert!(obj.vmap::<{ PAGE_SIZE + 200 }>().is_err());