[PATCH WIP 1/5] rust: Add soc_device support

[Matthew Maurer <mmaurer@google.com>]

Adds the ability to register SoC devices.

(This will be sent upstream in a separate request, it's uploaded now as
a dependency of the example driver.)

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 MAINTAINERS                     |   1 +
 rust/bindings/bindings_helper.h |   1 +
 rust/kernel/lib.rs              |   2 +
 rust/kernel/soc.rs              | 137 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 141 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 2cbe890085dbb6a652623b38dd0eadeeaa127a94..e0ff2731f1c2ae4bb01d361e99c1f4517fbd45d5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7481,6 +7481,7 @@ F:	rust/kernel/devres.rs
 F:	rust/kernel/driver.rs
 F:	rust/kernel/faux.rs
 F:	rust/kernel/platform.rs
+F:	rust/kernel/soc.rs
 F:	samples/rust/rust_debugfs.rs
 F:	samples/rust/rust_scoped_debugfs.rs
 F:	samples/rust/rust_driver_platform.rs
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index e847820dc807fdda2d682d496a3c6361bb944c10..140e2f4e60c0b745ac5d5c7456d60af28e21f55a 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -72,6 +72,7 @@
 #include <linux/sched.h>
 #include <linux/security.h>
 #include <linux/slab.h>
+#include <linux/sys_soc.h>
 #include <linux/tracepoint.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 828620c8441566a638f31d03633fc1bf4c1bda85..045f1088938cf646519edea2102439402fb27660 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -117,6 +117,8 @@
 pub mod security;
 pub mod seq_file;
 pub mod sizes;
+#[cfg(CONFIG_SOC_BUS)]
+pub mod soc;
 mod static_assert;
 #[doc(hidden)]
 pub mod std_vendor;
diff --git a/rust/kernel/soc.rs b/rust/kernel/soc.rs
new file mode 100644
index 0000000000000000000000000000000000000000..b8412751a5ca8839e588cf5bd52f2e6a7f33d457
--- /dev/null
+++ b/rust/kernel/soc.rs
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! SoC Driver Abstraction
+//!
+//! C header: [`include/linux/sys_soc.h`](srctree/include/linux/sys_soc.h)
+
+use crate::bindings;
+use crate::error;
+use crate::prelude::*;
+use crate::str::CString;
+use core::marker::PhantomPinned;
+use core::ptr::addr_of;
+
+/// Attributes for a SoC device
+pub struct DeviceAttribute {
+    /// Machine
+    pub machine: Option<CString>,
+    /// Family
+    pub family: Option<CString>,
+    /// Revision
+    pub revision: Option<CString>,
+    /// Serial Number
+    pub serial_number: Option<CString>,
+    /// SoC ID
+    pub soc_id: Option<CString>,
+}
+
+// SAFETY: We provide no operations through `&BuiltDeviceAttribute`
+unsafe impl Sync for BuiltDeviceAttribute {}
+
+// SAFETY: All pointers are normal allocations, not thread-specific
+unsafe impl Send for BuiltDeviceAttribute {}
+
+#[pin_data]
+struct BuiltDeviceAttribute {
+    #[pin]
+    backing: DeviceAttribute,
+    inner: bindings::soc_device_attribute,
+    // Since `inner` has pointers to `backing`, we are !Unpin
+    #[pin]
+    _pin: PhantomPinned,
+}
+
+fn cstring_to_c(mcs: &Option<CString>) -> *const kernel::ffi::c_char {
+    mcs.as_ref()
+        .map(|cs| cs.as_char_ptr())
+        .unwrap_or(core::ptr::null())
+}
+
+impl BuiltDeviceAttribute {
+    fn as_mut_ptr(&self) -> *mut bindings::soc_device_attribute {
+        core::ptr::from_ref(&self.inner).cast_mut()
+    }
+}
+
+impl DeviceAttribute {
+    fn build(self) -> impl PinInit<BuiltDeviceAttribute> {
+        pin_init!(BuiltDeviceAttribute {
+            inner: bindings::soc_device_attribute {
+                machine: cstring_to_c(&self.machine),
+                family: cstring_to_c(&self.family),
+                revision: cstring_to_c(&self.revision),
+                serial_number: cstring_to_c(&self.serial_number),
+                soc_id: cstring_to_c(&self.soc_id),
+                data: core::ptr::null(),
+                custom_attr_group: core::ptr::null(),
+            },
+            backing: self,
+            _pin: PhantomPinned,
+        })
+    }
+}
+
+// SAFETY: We provide no operations through &Device
+unsafe impl Sync for Device {}
+
+// SAFETY: Device holds a pointer to a `soc_device`, which may be sent to any thread.
+unsafe impl Send for Device {}
+
+/// A registered soc device
+#[repr(transparent)]
+pub struct Device(*mut bindings::soc_device);
+
+impl Device {
+    /// # Safety
+    /// * `attr` must be pinned
+    /// * `attr` must be valid for reads during the function call
+    /// * If a device is returned (e.g. no error), `attr` must remain valid for reads until the
+    ///   returned `Device` is dropped.
+    unsafe fn register(attr: *const BuiltDeviceAttribute) -> Result<Device> {
+        let raw_soc =
+            // SAFETY: The struct provided through attr is backed by pinned data next to it, so as
+            // long as attr lives, the strings pointed to by the struct will too. By caller
+            // invariant, `attr` is pinned, so the pinned data won't move. By caller invariant,
+            // `attr` is valid during this call. If it returns a device, and so others may try to
+            // read this data, by caller invariant, `attr` won't be released until the device is.
+            error::from_err_ptr(unsafe { bindings::soc_device_register((*attr).as_mut_ptr()) })?;
+        Ok(Device(raw_soc))
+    }
+}
+
+#[pin_data(PinnedDrop)]
+/// Registration handle for your soc_dev. If you let it go out of scope, your soc_dev will be
+/// unregistered.
+pub struct DeviceRegistration {
+    #[pin]
+    attr: BuiltDeviceAttribute,
+    soc_dev: Device,
+    // Since Device transitively points to the contents of attr, we are !Unpin
+    #[pin]
+    _pin: PhantomPinned,
+}
+
+#[pinned_drop]
+impl PinnedDrop for DeviceRegistration {
+    fn drop(self: Pin<&mut Self>) {
+        // SAFETY: Device always contains a live pointer to a soc_device that can be unregistered
+        unsafe { bindings::soc_device_unregister(self.soc_dev.0) }
+    }
+}
+
+impl DeviceRegistration {
+    /// Register a new SoC device
+    pub fn register(attr: DeviceAttribute) -> impl PinInit<Self, Error> {
+        try_pin_init!(&this in Self {
+                    attr <- attr.build(),
+                    // SAFETY: We have already initialized attr, and we are inside PinInit and Self
+                    // is !Unpin, so attr won't be moved and is valid. If it returns success, attr
+                    // will not be dropped until after our `PinnedDrop` implementation runs, so the
+                    // device will be unregistered first.
+                    soc_dev: unsafe { Device::register(addr_of!((*this.as_ptr()).attr))? },
+                    _pin: PhantomPinned,
+        }? Error)
+    }
+}

-- 
2.51.0.rc1.167.g924127e9c0-goog