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/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;