Merge patch series "rust: I/O type generalization and projection"

Gary Guo <gary@garyguo.net> says:

This series presents a major rework of I/O types, as a summary:

- Make I/O regions typed. The existing untyped region still exists
  with a dynamically sized `Region` type.

- Create I/O view types to represent subregion of a full I/O region mapped.
  A projection macro is added to allow safely create such subviews.

- Split I/O traits, make I/O views play a central role, avoid
  duplicate monomorphization and less `unsafe` code.

- Add a `SysMem` backend, and make `Coherent` implement `Io`.

- Add copying methods (memcpy_{from,to}io and friends).

This series generalize `Mmio` type from just an untyped region to typed
representations (so `MmioRaw<T>` is `__iomem *T`). This allows us to remove
the `IoKnownSize` trait; the information is sourced from just the pointer
from the `KnownSize` trait instead.

Building on top of that, `Mmio` and `ConfigSpace` have been converted to
typed views of I/O regions rather than just a big chunk of untyped I/O
memory. These changes made it possible to implement `Io` trait for
`Coherent<T>`.

Shared system memory, `SysMem` is also added to the series, given it
similarity in implementation compared to `Coherent`. In fact, the series
use `SysMem` to implement `Coherent`'s I/O methods.

Built on these generalization, this series add `io_project!()`.
`io_project!()` performs a safe way to project a bigger view to a small
subviews, and some Nova code has been converted in this series to
demonstrate cleanups possible with this addition.

New `io_read!()`, `io_write!()` has been added that supersedes
`dma_read!()`, `dma_write!()` macro. Although, they work for primitives
only (to be exact, types that the backend is `IoCapable` of).
One feature that was lost from the old `dma_read!()` and `dma_write!()`
series was the ability to read/write a large structs. However, the
semantics was unclear to begin with, as there was no guarantee about their
atomicity even for structs that were small enough to fit in u32.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Generic.20I.2FO.20backends/near/571198078
Link: https://patch.msgid.link/20260706-io_projection-v6-0-72cd5d055d54@garyguo.net
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

3 files changed, 43 insertions, 36 deletions

diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
index 931f2fa3bb10..32a919099dcd 100644
--- a/rust/kernel/io/mem.rs
+++ b/rust/kernel/io/mem.rs
@@ -2,8 +2,6 @@
 
 //! Generic memory-mapped IO.
 
-use core::ops::Deref;
-
 use crate::{
     device::{
         Bound,
@@ -16,7 +14,9 @@ use crate::{
             Region,
             Resource, //
         },
+        IoBase,
         Mmio,
+        MmioBackend,
         MmioRaw, //
     },
     prelude::*,
@@ -225,11 +225,13 @@ impl<'a, const SIZE: usize> ExclusiveIoMem<'a, SIZE> {
     }
 }
 
-impl<const SIZE: usize> Deref for ExclusiveIoMem<'_, SIZE> {
-    type Target = Mmio<SIZE>;
+impl<'a, const SIZE: usize> IoBase<'a> for &'a ExclusiveIoMem<'_, SIZE> {
+    type Backend = MmioBackend;
+    type Target = super::Region<SIZE>;
 
-    fn deref(&self) -> &Self::Target {
-        &self.iomem
+    #[inline]
+    fn as_view(self) -> Mmio<'a, Self::Target> {
+        self.iomem.as_view()
     }
 }
 
@@ -244,7 +246,7 @@ impl<const SIZE: usize> Deref for ExclusiveIoMem<'_, SIZE> {
 /// start of the I/O memory mapped region.
 pub struct IoMem<'a, const SIZE: usize = 0> {
     dev: &'a Device<Bound>,
-    io: MmioRaw<SIZE>,
+    io: MmioRaw<super::Region<SIZE>>,
 }
 
 impl<const SIZE: usize> ForLt for IoMem<'static, SIZE> {
@@ -292,8 +294,7 @@ impl<'a, const SIZE: usize> IoMem<'a, SIZE> {
             return Err(ENOMEM);
         }
 
-        let io = MmioRaw::new(addr as usize, size)?;
-
+        let io = MmioRaw::new_region(addr as usize, size)?;
         Ok(IoMem { dev, io })
     }
 
@@ -316,11 +317,13 @@ impl<const SIZE: usize> Drop for IoMem<'_, SIZE> {
     }
 }
 
-impl<const SIZE: usize> Deref for IoMem<'_, SIZE> {
-    type Target = Mmio<SIZE>;
+impl<'a, const SIZE: usize> IoBase<'a> for &'a IoMem<'_, SIZE> {
+    type Backend = MmioBackend;
+    type Target = super::Region<SIZE>;
 
-    fn deref(&self) -> &Self::Target {
+    #[inline]
+    fn as_view(self) -> Mmio<'a, Self::Target> {
         // SAFETY: Safe as by the invariant of `IoMem`.
-        unsafe { Mmio::from_raw(&self.io) }
+        unsafe { Mmio::from_raw(self.io) }
     }
 }
diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
index 75d1b3e8596c..d75f2fcf46f2 100644
--- a/rust/kernel/io/poll.rs
+++ b/rust/kernel/io/poll.rs
@@ -48,13 +48,14 @@ use crate::{
 /// use kernel::io::{
 ///     Io,
 ///     Mmio,
+///     Region,
 ///     poll::read_poll_timeout, //
 /// };
 /// use kernel::time::Delta;
 ///
 /// const HW_READY: u16 = 0x01;
 ///
-/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) -> Result {
+/// fn wait_for_hardware<const SIZE: usize>(io: Mmio<'_, Region<SIZE>>) -> Result {
 ///     read_poll_timeout(
 ///         // The `op` closure reads the value of a specific status register.
 ///         || io.try_read16(0x1000),
@@ -135,13 +136,14 @@ where
 /// use kernel::io::{
 ///     Io,
 ///     Mmio,
+///     Region,
 ///     poll::read_poll_timeout_atomic, //
 /// };
 /// use kernel::time::Delta;
 ///
 /// const HW_READY: u16 = 0x01;
 ///
-/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) -> Result {
+/// fn wait_for_hardware<const SIZE: usize>(io: Mmio<'_, Region<SIZE>>) -> Result {
 ///     read_poll_timeout_atomic(
 ///         // The `op` closure reads the value of a specific status register.
 ///         || io.try_read16(0x1000),
diff --git a/rust/kernel/io/register.rs b/rust/kernel/io/register.rs
index 66449377a0b7..6cb07fc92cc3 100644
--- a/rust/kernel/io/register.rs
+++ b/rust/kernel/io/register.rs
@@ -58,7 +58,7 @@
 //!     },
 //!     num::Bounded,
 //! };
-//! # use kernel::io::Mmio;
+//! # use kernel::io::{Mmio, Region};
 //! # register! {
 //! #     pub BOOT_0(u32) @ 0x00000100 {
 //! #         15:8 vendor_id;
@@ -66,7 +66,7 @@
 //! #         3:0 minor_revision;
 //! #     }
 //! # }
-//! # fn test(io: &Mmio<0x1000>) {
+//! # fn test(io: Mmio<'_, Region<0x1000>>) {
 //! # fn obtain_vendor_id() -> u8 { 0xff }
 //!
 //! // Read from the register's defined offset (0x100).
@@ -113,6 +113,8 @@ use crate::{
     io::IoLoc, //
 };
 
+use super::Region;
+
 /// Trait implemented by all registers.
 pub trait Register: Sized {
     /// Backing primitive type of the register.
@@ -129,7 +131,7 @@ pub trait FixedRegister: Register {}
 
 /// Allows `()` to be used as the `location` parameter of [`Io::write`](super::Io::write) when
 /// passing a [`FixedRegister`] value.
-impl<T> IoLoc<T> for ()
+impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for ()
 where
     T: FixedRegister,
 {
@@ -143,7 +145,7 @@ where
 
 /// A [`FixedRegister`] carries its location in its type. Thus `FixedRegister` values can be used
 /// as an [`IoLoc`].
-impl<T> IoLoc<T> for T
+impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for T
 where
     T: FixedRegister,
 {
@@ -168,7 +170,7 @@ impl<T: FixedRegister> FixedRegisterLoc<T> {
     }
 }
 
-impl<T> IoLoc<T> for FixedRegisterLoc<T>
+impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for FixedRegisterLoc<T>
 where
     T: FixedRegister,
 {
@@ -239,7 +241,7 @@ where
     }
 }
 
-impl<T, B> IoLoc<T> for RelativeRegisterLoc<T, B>
+impl<const SIZE: usize, T, B> IoLoc<Region<SIZE>, T> for RelativeRegisterLoc<T, B>
 where
     T: RelativeRegister,
     B: RegisterBase<T::BaseFamily> + ?Sized,
@@ -283,7 +285,7 @@ impl<T: RegisterArray> RegisterArrayLoc<T> {
     }
 }
 
-impl<T> IoLoc<T> for RegisterArrayLoc<T>
+impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for RegisterArrayLoc<T>
 where
     T: RegisterArray,
 {
@@ -370,7 +372,7 @@ where
     }
 }
 
-impl<T, B> IoLoc<T> for RelativeRegisterArrayLoc<T, B>
+impl<const SIZE: usize, T, B> IoLoc<Region<SIZE>, T> for RelativeRegisterArrayLoc<T, B>
 where
     T: RelativeRegisterArray,
     B: RegisterBase<T::BaseFamily> + ?Sized,
@@ -387,18 +389,18 @@ where
 /// which to write it.
 ///
 /// Implementors can be used with [`Io::write_reg`](super::Io::write_reg).
-pub trait LocatedRegister {
+pub trait LocatedRegister<Base: ?Sized> {
     /// Register value to write.
     type Value: Register;
     /// Full location information at which to write the value.
-    type Location: IoLoc<Self::Value>;
+    type Location: IoLoc<Base, Self::Value>;
 
     /// Consumes `self` and returns a `(location, value)` tuple describing a valid I/O write
     /// operation.
     fn into_io_op(self) -> (Self::Location, Self::Value);
 }
 
-impl<T> LocatedRegister for T
+impl<const SIZE: usize, T> LocatedRegister<Region<SIZE>> for T
 where
     T: FixedRegister,
 {
@@ -444,7 +446,7 @@ where
 ///         Io,
 ///     },
 /// };
-/// # use kernel::io::Mmio;
+/// # use kernel::io::{Mmio, Region};
 ///
 /// register! {
 ///     FIXED_REG(u32) @ 0x100 {
@@ -453,7 +455,7 @@ where
 ///     }
 /// }
 ///
-/// # fn test(io: &Mmio<0x1000>) {
+/// # fn test(io: Mmio<'_, Region<0x1000>>) {
 /// let val = io.read(FIXED_REG);
 ///
 /// // Write from an already-existing value.
@@ -557,7 +559,7 @@ where
 ///         Io,
 ///     },
 /// };
-/// # use kernel::io::Mmio;
+/// # use kernel::io::{Mmio, Region};
 ///
 /// // Type used to identify the base.
 /// pub struct CpuCtlBase;
@@ -582,7 +584,7 @@ where
 ///     }
 /// }
 ///
-/// # fn test(io: Mmio<0x1000>) {
+/// # fn test(io: Mmio<'_, Region<0x1000>>) {
 /// // Read the status of `Cpu0`.
 /// let cpu0_started = io.read(CPU_CTL::of::<Cpu0>());
 ///
@@ -599,7 +601,7 @@ where
 ///     }
 /// }
 ///
-/// # fn test2(io: Mmio<0x1000>) {
+/// # fn test2(io: Mmio<'_, Region<0x1000>>) {
 /// // Start the aliased `CPU0`, leaving its other fields untouched.
 /// io.update(CPU_CTL_ALIAS::of::<Cpu0>(), |r| r.with_alias_start(true));
 /// # }
@@ -636,7 +638,7 @@ where
 ///         Io,
 ///     },
 /// };
-/// # use kernel::io::Mmio;
+/// # use kernel::io::{Mmio, Region};
 /// # fn get_scratch_idx() -> usize {
 /// #   0x15
 /// # }
@@ -649,7 +651,7 @@ where
 ///     }
 /// }
 ///
-/// # fn test(io: &Mmio<0x1000>)
+/// # fn test(io: Mmio<'_, Region<0x1000>>)
 /// #     -> Result<(), Error>{
 /// // Read scratch register 0, i.e. I/O address `0x80`.
 /// let scratch_0 = io.read(SCRATCH::at(0)).value();
@@ -722,7 +724,7 @@ where
 ///         Io,
 ///     },
 /// };
-/// # use kernel::io::Mmio;
+/// # use kernel::io::{Mmio, Region};
 /// # fn get_scratch_idx() -> usize {
 /// #   0x15
 /// # }
@@ -750,7 +752,7 @@ where
 ///     }
 /// }
 ///
-/// # fn test(io: &Mmio<0x1000>) -> Result<(), Error> {
+/// # fn test(io: Mmio<'_, Region<0x1000>>) -> Result<(), Error> {
 /// // Read scratch register 0 of CPU0.
 /// let scratch = io.read(CPU_SCRATCH::of::<Cpu0>().at(0));
 ///
@@ -792,7 +794,7 @@ where
 ///     }
 /// }
 ///
-/// # fn test2(io: &Mmio<0x1000>) -> Result<(), Error> {
+/// # fn test2(io: Mmio<'_, Region<0x1000>>) -> Result<(), Error> {
 /// let cpu0_status = io.read(CPU_FIRMWARE_STATUS::of::<Cpu0>()).status();
 /// # Ok(())
 /// # }