Add RISC-V timer support

kernel/comps/time/src/rtc/goldfish.rs

@@ -1,28 +1,40 @@
 // SPDX-License-Identifier: MPL-2.0
 
-use ostd::{arch::timer::GOLDFISH_IO_MEM, mm::VmIoOnce};
+use ostd::{arch::boot::DEVICE_TREE, io::IoMem, mm::VmIoOnce};
 use chrono::{DateTime, Datelike, Timelike};
 
 use crate::{SystemTime, rtc::Driver};
 
-pub struct RtcGoldfish;
+pub struct RtcGoldfish {
+    io_mem: IoMem,
+}
 
 impl Driver for RtcGoldfish {
     fn try_new() -> Option<RtcGoldfish> {
-        GOLDFISH_IO_MEM.get()?;
-        Some(RtcGoldfish)
+        let chosen = DEVICE_TREE.get().unwrap().find_node("/soc/rtc").unwrap();
+        if let Some(compatible) = chosen.compatible()
+            && compatible.all().any(|c| c == "google,goldfish-rtc")
+        {
+            let region = chosen.reg().unwrap().next().unwrap();
+            let io_mem = IoMem::acquire(
+                region.starting_address as usize
+                    ..region.starting_address as usize + region.size.unwrap(),
+            )
+            .unwrap();
+            Some(RtcGoldfish { io_mem })
+        } else {
+            None
+        }
     }
 
     fn read_rtc(&self) -> SystemTime {
         const TIME_LOW: usize = 0;
         const TIME_HIGH: usize = 4;
 
-        let io_mem = GOLDFISH_IO_MEM.get().unwrap();
-
-        let mut last_time_high = io_mem.read_once(TIME_HIGH).unwrap();
+        let mut last_time_high = self.io_mem.read_once(TIME_HIGH).unwrap();
         let timestamp = loop {
-            let time_low: u32 = io_mem.read_once(TIME_LOW).unwrap();
-            let time_high: u32 = io_mem.read_once(TIME_HIGH).unwrap();
+            let time_low: u32 = self.io_mem.read_once(TIME_LOW).unwrap();
+            let time_high: u32 = self.io_mem.read_once(TIME_HIGH).unwrap();
             if last_time_high == time_high {
                 break ((time_high as u64) << 32) | time_low as u64;
             }

ostd/src/arch/riscv/cpu/context.rs

@@ -4,11 +4,14 @@
 
 use core::fmt::Debug;
 
-use riscv::register::scause::{Exception, Trap};
+use riscv::register::scause::{Exception, Interrupt, Trap};
 
 pub use crate::arch::trap::GeneralRegs as RawGeneralRegs;
 use crate::{
-    arch::trap::{TrapFrame, UserContext as RawUserContext},
+    arch::{
+        timer::handle_timer_interrupt,
+        trap::{TrapFrame, UserContext as RawUserContext},
+    },
     user::{ReturnReason, UserContextApi, UserContextApiInternal},
 };
 
@@ -111,6 +114,9 @@ impl UserContextApiInternal for UserContext {
         let ret = loop {
             self.user_context.run();
             match riscv::register::scause::read().cause() {
+                Trap::Interrupt(Interrupt::SupervisorTimer) => {
+                    handle_timer_interrupt();
+                }
                 Trap::Interrupt(_) => todo!(),
                 Trap::Exception(Exception::UserEnvCall) => {
                     self.user_context.sepc += 4;

ostd/src/arch/riscv/mod.rs

@@ -15,8 +15,6 @@ pub mod task;
 pub mod timer;
 pub mod trap;
 
-use core::sync::atomic::Ordering;
-
 #[cfg(feature = "cvm_guest")]
 pub(crate) fn init_cvm_guest() {
     // Unimplemented, no-op
@@ -29,7 +27,10 @@ pub(crate) unsafe fn late_init_on_bsp() {
     // SAFETY: We're on the BSP and we're ready to boot all APs.
     unsafe { crate::boot::smp::boot_all_aps() };
 
-    timer::init();
+    // SAFETY: This function is called once and at most once at a proper timing
+    // in the boot context of the BSP, with no timer-related operations having
+    // been performed.
+    unsafe { timer::init() };
     let _ = pci::init();
 }
 
@@ -43,7 +44,7 @@ pub(crate) fn interrupts_ack(irq_number: usize) {
 
 /// Return the frequency of TSC. The unit is Hz.
 pub fn tsc_freq() -> u64 {
-    timer::TIMEBASE_FREQ.load(Ordering::Relaxed)
+    timer::get_timebase_freq()
 }
 
 /// Reads the current value of the processor’s time-stamp counter (TSC).

ostd/src/arch/riscv/timer/mod.rs

@@ -2,48 +2,123 @@
 
 //! The timer support.
 
-use core::sync::atomic::{AtomicU64, Ordering};
+use core::{
+    arch::asm,
+    sync::atomic::{AtomicU64, Ordering},
+};
 
-use spin::Once;
+use crate::{
+    arch::boot::DEVICE_TREE,
+    cpu::{CpuId, PinCurrentCpu},
+    timer::INTERRUPT_CALLBACKS,
+    trap,
+};
 
-use crate::{arch::boot::DEVICE_TREE, io::IoMem};
-
-/// The timer frequency (Hz). Here we choose 1000Hz since 1000Hz is easier for unit conversion and
-/// convenient for timer. What's more, the frequency cannot be set too high or too low, 1000Hz is
-/// a modest choice.
+/// The timer frequency (Hz). Here we choose 1000Hz since 1000Hz is easier for
+/// unit conversion and convenient for timer. What's more, the frequency cannot
+/// be set too high or too low, 1000Hz is a modest choice.
 ///
-/// For system performance reasons, this rate cannot be set too high, otherwise most of the time
-/// is spent executing timer code.
+/// For system performance reasons, this rate cannot be set too high, otherwise
+/// most of the time is spent executing timer code.
 pub const TIMER_FREQ: u64 = 1000;
 
-pub(crate) static TIMEBASE_FREQ: AtomicU64 = AtomicU64::new(1);
+static TIMEBASE_FREQ: AtomicU64 = AtomicU64::new(0);
+static TIMER_INTERVAL: AtomicU64 = AtomicU64::new(0);
 
-/// [`IoMem`] of goldfish RTC, which will be used by `aster-time`.
-pub static GOLDFISH_IO_MEM: Once<IoMem> = Once::new();
-
-pub(super) fn init() {
-    let timer_freq = DEVICE_TREE
+/// Initializes the timer module.
+///
+/// # Safety
+///
+/// This function is safe to call on the following conditions:
+/// 1. It is called once and at most once at a proper timing in the boot context.
+/// 2. It is called before any other public functions of this module is called.
+pub(super) unsafe fn init() {
+    TIMEBASE_FREQ.store(
+        DEVICE_TREE
             .get()
             .unwrap()
             .cpus()
             .next()
             .unwrap()
-        .timebase_frequency() as u64;
-    TIMEBASE_FREQ.store(timer_freq, Ordering::Relaxed);
+            .timebase_frequency() as u64,
+        Ordering::Relaxed,
+    );
+    TIMER_INTERVAL.store(
+        TIMEBASE_FREQ.load(Ordering::Relaxed) / TIMER_FREQ,
+        Ordering::Relaxed,
+    );
 
-    let chosen = DEVICE_TREE.get().unwrap().find_node("/soc/rtc").unwrap();
-    if let Some(compatible) = chosen.compatible()
-        && compatible.all().any(|c| c == "google,goldfish-rtc")
-    {
-        let region = chosen.reg().unwrap().next().unwrap();
-        let io_mem = unsafe {
-            IoMem::new(
-                (region.starting_address as usize)
-                    ..(region.starting_address as usize) + region.size.unwrap(),
-                crate::mm::page_prop::PageFlags::RW,
-                crate::mm::page_prop::CachePolicy::Uncacheable,
-            )
-        };
-        GOLDFISH_IO_MEM.call_once(|| io_mem);
+    if is_sstc_enabled() {
+        // SAFETY: Mutating the static variable `SET_NEXT_TIMER_FN` is safe here
+        // because we ensure that it is only modified during the initialization
+        // phase of the timer.
+        unsafe {
+            SET_NEXT_TIMER_FN = set_next_timer_sstc;
+        }
+    }
+    set_next_timer();
+    // SAFETY: Accessing the `sie` CSR to enable the timer interrupt is safe
+    // here because this function is only called during timer initialization,
+    // and we ensure that only the timer interrupt bit is set without affecting
+    // other interrupt sources.
+    unsafe {
+        riscv::register::sie::set_stimer();
     }
 }
+
+pub(super) fn handle_timer_interrupt() {
+    let irq_guard = trap::disable_local();
+    if irq_guard.current_cpu() == CpuId::bsp() {
+        crate::timer::jiffies::ELAPSED.fetch_add(1, Ordering::Relaxed);
+    }
+
+    let callbacks_guard = INTERRUPT_CALLBACKS.get_with(&irq_guard);
+    for callback in callbacks_guard.borrow().iter() {
+        (callback)();
+    }
+    drop(callbacks_guard);
+
+    set_next_timer();
+}
+
+fn set_next_timer() {
+    // SAFETY: Calling the `SET_NEXT_TIMER_FN` function pointer is safe here
+    // because we ensure that it is set to a valid function during the timer
+    // initialization, and we never modify it after that.
+    unsafe {
+        SET_NEXT_TIMER_FN();
+    }
+}
+
+static mut SET_NEXT_TIMER_FN: fn() = set_next_timer_sbi;
+
+fn set_next_timer_sbi() {
+    sbi_rt::set_timer(TIMER_INTERVAL.load(Ordering::Relaxed));
+}
+
+fn set_next_timer_sstc() {
+    // SAFETY: Setting the next timer using the `stimecmp` CSR is safe here
+    // because we are using the `stimecmp` CSR to set the next timer interrupt
+    // only when we're handling a timer interrupt, which is a standard operation
+    // specified by RISC-V SSTC extension.
+    unsafe {
+        asm!("csrrw {}, stimecmp, {}", out(reg) _, in(reg) get_next_when());
+    }
+}
+
+fn is_sstc_enabled() -> bool {
+    let Some(misa) = riscv::register::misa::read() else {
+        return false;
+    };
+    misa.has_extension('S')
+}
+
+fn get_next_when() -> u64 {
+    let current = riscv::register::time::read64();
+    let interval = TIMER_INTERVAL.load(Ordering::Relaxed);
+    current + interval
+}
+
+pub(crate) fn get_timebase_freq() -> u64 {
+    TIMEBASE_FREQ.load(Ordering::Relaxed)
+}

ostd/src/arch/riscv/trap/mod.rs

@@ -4,6 +4,7 @@
 
 mod trap;
 
+use riscv::register::scause::Interrupt;
 use spin::Once;
 pub use trap::{GeneralRegs, TrapFrame, UserContext};
 
@@ -32,9 +33,20 @@ extern "C" fn trap_handler(f: &mut TrapFrame) {
     use riscv::register::scause::Trap;
 
     match riscv::register::scause::read().cause() {
-        Trap::Interrupt(_) => {
+        Trap::Interrupt(interrupt) => {
             IS_KERNEL_INTERRUPTED.store(true);
-            todo!();
+            match interrupt {
+                Interrupt::SupervisorTimer => {
+                    crate::arch::timer::handle_timer_interrupt();
+                }
+                Interrupt::SupervisorExternal => todo!(),
+                Interrupt::SupervisorSoft => todo!(),
+                _ => {
+                    panic!(
+                        "cannot handle unknown supervisor interrupt: {interrupt:?}. trapframe: {f:#x?}.",
+                    );
+                }
+            }
             IS_KERNEL_INTERRUPTED.store(false);
         }
         Trap::Exception(e) => {