rust/timer/hpet: define hpet_fw_cfg

Define HPETFwEntry structure with the same memory layout as
hpet_fw_entry in C.

Further, define the global hpet_cfg variable in Rust which is the
same as the C version. This hpet_cfg variable in Rust will replace
the C version one and allows both Rust code and C code to access it.

The Rust version of hpet_cfg is self-contained, avoiding unsafe
access to C code.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250210030051.2562726-8-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/Cargo.lock

@@ -37,6 +37,14 @@ version = "1.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3dca9240753cf90908d7e4aac30f630662b02aebaa1b58a3cadabdb23385b58b"
 
+[[package]]
+name = "hpet"
+version = "0.1.0"
+dependencies = [
+ "qemu_api",
+ "qemu_api_macros",
+]
+
 [[package]]
 name = "itertools"
 version = "0.11.0"

rust/Cargo.toml

@@ -4,6 +4,7 @@ members = [
     "qemu-api-macros",
     "qemu-api",
     "hw/char/pl011",
+    "hw/timer/hpet",
 ]
 
 [workspace.lints.rust]

rust/hw/meson.build

@@ -1 +1,2 @@
 subdir('char')
+subdir('timer')

rust/hw/timer/hpet/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "hpet"
+version = "0.1.0"
+edition = "2021"
+authors = ["Zhao Liu <zhao1.liu@intel.com>"]
+license = "GPL-2.0-or-later"
+description = "IA-PC High Precision Event Timer emulation in Rust"
+rust-version = "1.63.0"
+
+[lib]
+crate-type = ["staticlib"]
+
+[dependencies]
+qemu_api = { path = "../../../qemu-api" }
+qemu_api_macros = { path = "../../../qemu-api-macros" }
+
+[lints]
+workspace = true

rust/hw/timer/hpet/meson.build

@@ -0,0 +1,18 @@
+_libhpet_rs = static_library(
+  'hpet',
+  files('src/lib.rs'),
+  override_options: ['rust_std=2021', 'build.rust_std=2021'],
+  rust_abi: 'rust',
+  dependencies: [
+    qemu_api,
+    qemu_api_macros,
+  ],
+)
+
+rust_devices_ss.add(when: 'CONFIG_X_HPET_RUST', if_true: [declare_dependency(
+  link_whole: [_libhpet_rs],
+  # Putting proc macro crates in `dependencies` is necessary for Meson to find
+  # them when compiling the root per-target static rust lib.
+  dependencies: [qemu_api_macros],
+  variables: {'crate': 'hpet'},
+)])

rust/hw/timer/hpet/src/fw_cfg.rs

@@ -0,0 +1,71 @@
+// Copyright (C) 2024 Intel Corporation.
+// Author(s): Zhao Liu <zhai1.liu@intel.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#![allow(dead_code)]
+
+use std::ptr::addr_of_mut;
+
+use qemu_api::{cell::bql_locked, impl_zeroable, zeroable::Zeroable};
+
+/// Each `HPETState` represents a Event Timer Block. The v1 spec supports
+/// up to 8 blocks. QEMU only uses 1 block (in PC machine).
+const HPET_MAX_NUM_EVENT_TIMER_BLOCK: usize = 8;
+
+#[repr(C, packed)]
+#[derive(Copy, Clone, Default)]
+pub struct HPETFwEntry {
+    pub event_timer_block_id: u32,
+    pub address: u64,
+    pub min_tick: u16,
+    pub page_prot: u8,
+}
+impl_zeroable!(HPETFwEntry);
+
+#[repr(C, packed)]
+#[derive(Copy, Clone, Default)]
+pub struct HPETFwConfig {
+    pub count: u8,
+    pub hpet: [HPETFwEntry; HPET_MAX_NUM_EVENT_TIMER_BLOCK],
+}
+impl_zeroable!(HPETFwConfig);
+
+#[allow(non_upper_case_globals)]
+#[no_mangle]
+pub static mut hpet_fw_cfg: HPETFwConfig = HPETFwConfig {
+    count: u8::MAX,
+    ..Zeroable::ZERO
+};
+
+impl HPETFwConfig {
+    pub(crate) fn assign_hpet_id() -> usize {
+        assert!(bql_locked());
+        // SAFETY: all accesses go through these methods, which guarantee
+        // that the accesses are protected by the BQL.
+        let mut fw_cfg = unsafe { *addr_of_mut!(hpet_fw_cfg) };
+
+        if fw_cfg.count == u8::MAX {
+            // first instance
+            fw_cfg.count = 0;
+        }
+
+        if fw_cfg.count == 8 {
+            // TODO: Add error binding: error_setg()
+            panic!("Only 8 instances of HPET is allowed");
+        }
+
+        let id: usize = fw_cfg.count.into();
+        fw_cfg.count += 1;
+        id
+    }
+
+    pub(crate) fn update_hpet_cfg(hpet_id: usize, timer_block_id: u32, address: u64) {
+        assert!(bql_locked());
+        // SAFETY: all accesses go through these methods, which guarantee
+        // that the accesses are protected by the BQL.
+        let mut fw_cfg = unsafe { *addr_of_mut!(hpet_fw_cfg) };
+
+        fw_cfg.hpet[hpet_id].event_timer_block_id = timer_block_id;
+        fw_cfg.hpet[hpet_id].address = address;
+    }
+}

rust/hw/timer/hpet/src/lib.rs

@@ -0,0 +1,10 @@
+// Copyright (C) 2024 Intel Corporation.
+// Author(s): Zhao Liu <zhai1.liu@intel.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! # HPET QEMU Device Model
+//!
+//! This library implements a device model for the IA-PC HPET (High
+//! Precision Event Timers) device in QEMU.
+
+pub mod fw_cfg;

rust/hw/timer/meson.build

@@ -0,0 +1 @@
+subdir('hpet')

rust/qemu-api/src/zeroable.rs

@@ -56,6 +56,7 @@ pub unsafe trait Zeroable: Default {
 /// ## Differences with `core::mem::zeroed`
 ///
 /// `const_zero` zeroes padding bits, while `core::mem::zeroed` doesn't
+#[macro_export]
 macro_rules! const_zero {
     // This macro to produce a type-generic zero constant is taken from the
     // const_zero crate (v0.1.1):
@@ -77,10 +78,11 @@ union TypeAsBytes {
 }
 
 /// A wrapper to implement the `Zeroable` trait through the `const_zero` macro.
+#[macro_export]
 macro_rules! impl_zeroable {
     ($type:ty) => {
-        unsafe impl Zeroable for $type {
-            const ZERO: Self = unsafe { const_zero!($type) };
+        unsafe impl $crate::zeroable::Zeroable for $type {
+            const ZERO: Self = unsafe { $crate::const_zero!($type) };
         }
     };
 }