rust: soc: apple: rtkit: Add Apple RTKit abstraction

RTKit is Apple's proprietary real-time operating system framework, used
across many subdevices on Apple Silicon platforms including NVMe, system
management, GPU, etc. Add Rust abstractions for this subsystem, so that
it can be used by upcoming Rust drivers.

Note: Although ARM64 support is not yet merged, this can be built on amd64
with CONFIG_COMPILE_TEST=y.

FIXME: order in drivers/soc/apple/Kconfig to avoid merge conflicts in
asahi tree

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

drivers/soc/apple/Kconfig

@@ -41,6 +41,11 @@ config APPLE_SART
 
 	  Say 'y' here if you have an Apple SoC.
 
+config RUST_APPLE_RTKIT
+	bool
+	depends on RUST
+	depends on APPLE_RTKIT
+
 endmenu
 
 endif

rust/bindings/bindings_helper.h

@@ -32,6 +32,7 @@
 #include <linux/siphash.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/soc/apple/rtkit.h>
 #include <linux/timekeeping.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>

rust/kernel/lib.rs

@@ -67,6 +67,7 @@ pub mod rbtree;
 pub mod revocable;
 pub mod siphash;
 pub mod sizes;
+pub mod soc;
 mod static_assert;
 #[doc(hidden)]
 pub mod std_vendor;

rust/kernel/soc/apple/mod.rs

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+
+//! Apple SoC drivers
+
+#[cfg(CONFIG_APPLE_RTKIT = "y")]
+pub mod rtkit;

rust/kernel/soc/apple/rtkit.rs

@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+
+//! Support for Apple RTKit coprocessors.
+//!
+//! C header: [`include/linux/soc/apple/rtkit.h`](../../../../include/linux/gpio/driver.h)
+
+use crate::{
+    alloc::{box_ext::BoxExt, flags::*},
+    bindings, device,
+    error::{code::*, from_err_ptr, from_result, to_result, Result},
+    str::CStr,
+    types::{ForeignOwnable, ScopeGuard},
+};
+
+use alloc::boxed::Box;
+use core::marker::PhantomData;
+use core::ptr;
+use macros::vtable;
+
+/// Trait to represent allocatable buffers for the RTKit core.
+///
+/// Users must implement this trait for their own representation of those allocations.
+pub trait Buffer {
+    /// Returns the IOVA (virtual address) of the buffer from RTKit's point of view, or an error if
+    /// unavailable.
+    fn iova(&self) -> Result<usize>;
+
+    /// Returns a mutable byte slice of the buffer contents, or an
+    /// error if unavailable.
+    fn buf(&mut self) -> Result<&mut [u8]>;
+}
+
+/// Callback operations for an RTKit client.
+#[vtable]
+pub trait Operations {
+    /// Arbitrary user context type.
+    type Data: ForeignOwnable + Send + Sync;
+
+    /// Type representing an allocated buffer for RTKit.
+    type Buffer: Buffer;
+
+    /// Called when RTKit crashes.
+    fn crashed(_data: <Self::Data as ForeignOwnable>::Borrowed<'_>) {}
+
+    /// Called when a message was received on a non-system endpoint. Called in non-IRQ context.
+    fn recv_message(
+        _data: <Self::Data as ForeignOwnable>::Borrowed<'_>,
+        _endpoint: u8,
+        _message: u64,
+    ) {
+    }
+
+    /// Called in IRQ context when a message was received on a non-system endpoint.
+    ///
+    /// Must return `true` if the message is handled, or `false` to process it in
+    /// the handling thread.
+    fn recv_message_early(
+        _data: <Self::Data as ForeignOwnable>::Borrowed<'_>,
+        _endpoint: u8,
+        _message: u64,
+    ) -> bool {
+        false
+    }
+
+    /// Allocate a buffer for use by RTKit.
+    fn shmem_alloc(
+        _data: <Self::Data as ForeignOwnable>::Borrowed<'_>,
+        _size: usize,
+    ) -> Result<Self::Buffer> {
+        Err(EINVAL)
+    }
+
+    /// Map an existing buffer used by RTKit at a device-specified virtual address.
+    fn shmem_map(
+        _data: <Self::Data as ForeignOwnable>::Borrowed<'_>,
+        _iova: usize,
+        _size: usize,
+    ) -> Result<Self::Buffer> {
+        Err(EINVAL)
+    }
+}
+
+/// Represents `struct apple_rtkit *`.
+///
+/// # Invariants
+///
+/// The rtk pointer is valid.
+/// The data pointer is a valid pointer from T::Data::into_foreign().
+pub struct RtKit<T: Operations> {
+    rtk: *mut bindings::apple_rtkit,
+    data: *mut core::ffi::c_void,
+    _p: PhantomData<T>,
+}
+
+unsafe extern "C" fn crashed_callback<T: Operations>(cookie: *mut core::ffi::c_void) {
+    // SAFETY: cookie is always a T::Data in this API
+    T::crashed(unsafe { T::Data::borrow(cookie) });
+}
+
+unsafe extern "C" fn recv_message_callback<T: Operations>(
+    cookie: *mut core::ffi::c_void,
+    endpoint: u8,
+    message: u64,
+) {
+    // SAFETY: cookie is always a T::Data in this API
+    T::recv_message(unsafe { T::Data::borrow(cookie) }, endpoint, message);
+}
+
+unsafe extern "C" fn recv_message_early_callback<T: Operations>(
+    cookie: *mut core::ffi::c_void,
+    endpoint: u8,
+    message: u64,
+) -> bool {
+    // SAFETY: cookie is always a T::Data in this API
+    T::recv_message_early(unsafe { T::Data::borrow(cookie) }, endpoint, message)
+}
+
+unsafe extern "C" fn shmem_setup_callback<T: Operations>(
+    cookie: *mut core::ffi::c_void,
+    bfr: *mut bindings::apple_rtkit_shmem,
+) -> core::ffi::c_int {
+    // SAFETY: `bfr` is a valid buffer
+    let bfr_mut = unsafe { &mut *bfr };
+
+    from_result(|| {
+        let mut buf = if bfr_mut.iova != 0 {
+            bfr_mut.is_mapped = true;
+            T::shmem_map(
+                // SAFETY: `cookie` came from a previous call to `into_foreign`.
+                unsafe { T::Data::borrow(cookie) },
+                bfr_mut.iova as usize,
+                bfr_mut.size,
+            )?
+        } else {
+            bfr_mut.is_mapped = false;
+            // SAFETY: `cookie` came from a previous call to `into_foreign`.
+            T::shmem_alloc(unsafe { T::Data::borrow(cookie) }, bfr_mut.size)?
+        };
+
+        let iova = buf.iova()?;
+        let slice = buf.buf()?;
+
+        if slice.len() < bfr_mut.size {
+            return Err(ENOMEM);
+        }
+
+        bfr_mut.iova = iova as u64;
+        bfr_mut.buffer = slice.as_mut_ptr() as *mut _;
+
+        // Now box the returned buffer type and stash it in the private pointer of the
+        // `apple_rtkit_shmem` struct for safekeeping.
+        let boxed = Box::new(buf, GFP_KERNEL)?;
+        bfr_mut.private = Box::into_raw(boxed) as *mut _;
+        Ok(0)
+    })
+}
+
+unsafe extern "C" fn shmem_destroy_callback<T: Operations>(
+    _cookie: *mut core::ffi::c_void,
+    bfr: *mut bindings::apple_rtkit_shmem,
+) {
+    // SAFETY: `bfr` is a valid buffer
+    let bfr_mut = unsafe { &mut *bfr };
+    if !bfr_mut.private.is_null() {
+        // SAFETY: Per shmem_setup_callback, this has to be a pointer to a Buffer if it is set.
+        unsafe {
+            core::mem::drop(Box::from_raw(bfr_mut.private as *mut T::Buffer));
+        }
+        bfr_mut.private = core::ptr::null_mut();
+    }
+}
+
+impl<T: Operations> RtKit<T> {
+    const VTABLE: bindings::apple_rtkit_ops = bindings::apple_rtkit_ops {
+        crashed: Some(crashed_callback::<T>),
+        recv_message: Some(recv_message_callback::<T>),
+        recv_message_early: Some(recv_message_early_callback::<T>),
+        shmem_setup: if T::HAS_SHMEM_ALLOC || T::HAS_SHMEM_MAP {
+            Some(shmem_setup_callback::<T>)
+        } else {
+            None
+        },
+        shmem_destroy: if T::HAS_SHMEM_ALLOC || T::HAS_SHMEM_MAP {
+            Some(shmem_destroy_callback::<T>)
+        } else {
+            None
+        },
+    };
+
+    /// Creates a new RTKit client for a given device and optional mailbox name or index.
+    pub fn new(
+        dev: &dyn device::RawDevice,
+        mbox_name: Option<&'static CStr>,
+        mbox_idx: usize,
+        data: T::Data,
+    ) -> Result<Self> {
+        let ptr = data.into_foreign() as *mut _;
+        let guard = ScopeGuard::new(|| {
+            // SAFETY: `ptr` came from a previous call to `into_foreign`.
+            unsafe { T::Data::from_foreign(ptr) };
+        });
+        // SAFETY: This just calls the C init function.
+        let rtk = unsafe {
+            from_err_ptr(bindings::apple_rtkit_init(
+                dev.raw_device(),
+                ptr,
+                match mbox_name {
+                    Some(s) => s.as_char_ptr(),
+                    None => ptr::null(),
+                },
+                mbox_idx.try_into()?,
+                &Self::VTABLE,
+            ))
+        }?;
+
+        guard.dismiss();
+        // INVARIANT: `rtk` and `data` are valid here.
+        Ok(Self {
+            rtk,
+            data: ptr,
+            _p: PhantomData,
+        })
+    }
+
+    /// Boots (wakes up) the RTKit coprocessor.
+    pub fn boot(&mut self) -> Result {
+        // SAFETY: `rtk` is valid per the type invariant.
+        to_result(unsafe { bindings::apple_rtkit_boot(self.rtk) })
+    }
+
+    /// Starts a non-system endpoint.
+    pub fn start_endpoint(&mut self, endpoint: u8) -> Result {
+        // SAFETY: `rtk` is valid per the type invariant.
+        to_result(unsafe { bindings::apple_rtkit_start_ep(self.rtk, endpoint) })
+    }
+
+    /// Sends a message to a given endpoint.
+    pub fn send_message(&mut self, endpoint: u8, message: u64) -> Result {
+        // SAFETY: `rtk` is valid per the type invariant.
+        to_result(unsafe {
+            bindings::apple_rtkit_send_message(self.rtk, endpoint, message, ptr::null_mut(), false)
+        })
+    }
+}
+
+// SAFETY: `RtKit` operations require a mutable reference
+unsafe impl<T: Operations> Sync for RtKit<T> {}
+
+// SAFETY: `RtKit` operations require a mutable reference
+unsafe impl<T: Operations> Send for RtKit<T> {}
+
+impl<T: Operations> Drop for RtKit<T> {
+    fn drop(&mut self) {
+        // SAFETY: The pointer is valid by the type invariant.
+        unsafe { bindings::apple_rtkit_free(self.rtk) };
+
+        // Free context data.
+        //
+        // SAFETY: This matches the call to `into_foreign` from `new` in the success case.
+        unsafe { T::Data::from_foreign(self.data) };
+    }
+}

rust/kernel/soc/mod.rs

@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! SoC drivers
+
+pub mod apple;