Add support for the WAET ACPI table (theseus-os#1050)

* Currently not used, but fully working.
* Can be used to optimize RTC and ACPI PM timer usage.

kernel/acpi/Cargo.toml

@@ -27,6 +27,9 @@ path = "rsdt"
 [dependencies.fadt]
 path = "fadt"
 
+[dependencies.waet]
+path = "waet"
+
 [dependencies.madt]
 path = "madt"
 

kernel/acpi/acpi_table_handler/Cargo.toml

@@ -20,6 +20,9 @@ path = "../rsdt"
 [dependencies.fadt]
 path = "../fadt"
 
+[dependencies.waet]
+path = "../waet"
+
 [dependencies.hpet]
 path = "../hpet"
 

kernel/acpi/acpi_table_handler/src/lib.rs

@@ -35,6 +35,7 @@ pub fn acpi_table_handler(
         rsdt::RSDT_SIGNATURE |
         rsdt::XSDT_SIGNATURE => rsdt::handle(acpi_tables, signature, length, phys_addr),
         fadt::FADT_SIGNATURE => fadt::handle(acpi_tables, signature, length, phys_addr),
+        waet::WAET_SIGNATURE => waet::handle(acpi_tables, signature, length, phys_addr),
         hpet::HPET_SIGNATURE => hpet::handle(acpi_tables, signature, length, phys_addr),
         madt::MADT_SIGNATURE => madt::handle(acpi_tables, signature, length, phys_addr),
         dmar::DMAR_SIGNATURE => dmar::handle(acpi_tables, signature, length, phys_addr),

kernel/acpi/src/lib.rs

@@ -1,4 +1,4 @@
-//! Code to parse the ACPI tables, based off of Redox. 
+//! Code to parse the ACPI tables.
 #![no_std]
 
 extern crate alloc;
@@ -63,6 +63,17 @@ pub fn init(rsdp_address: Option<PhysicalAddress>, page_table: &mut PageTable) -
         // here: do something with the DSDT here, when needed.
         // debug!("DSDT physical address: {:#X}", {_fadt.dsdt});
     }
+
+    // WAET is optional, and contains info about potentially optimizing timer-related actions.
+    {
+        let acpi_tables = ACPI_TABLES.lock();
+        if let Some(waet) = waet::Waet::get(&acpi_tables) {
+            // here: do something with the WAET here, if desired.
+            debug!("WAET: RTC? {:?}. ACPI PM timer? {:?}",
+                waet.rtc_good(), waet.acpi_pm_timer_good(),
+            );
+        }
+    }
 
     // HPET is optional, but usually present.
     {

kernel/acpi/waet/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "waet"
+version = "0.1.0"
+authors = ["Kevin Boos <kevinaboos@gmail.com>"]
+description = "Support for ACPI WAET"
+edition = "2021"
+
+[dependencies]
+zerocopy = "0.5.0"
+
+[dependencies.memory]
+path = "../../memory"
+
+[dependencies.sdt]
+path = "../sdt"
+
+[dependencies.acpi_table]
+path = "../acpi_table"
+

kernel/acpi/waet/src/lib.rs

@@ -0,0 +1,63 @@
+//! Definitions for WAET, the Windows ACPI Emulated devices Table.
+
+#![no_std]
+
+use memory::PhysicalAddress;
+use sdt::Sdt;
+use acpi_table::{AcpiSignature, AcpiTables};
+use zerocopy::FromBytes;
+
+
+pub const WAET_SIGNATURE: &[u8; 4] = b"WAET";
+
+
+/// The handler for parsing the WAET table and adding it to the ACPI tables list.
+pub fn handle(
+    acpi_tables: &mut AcpiTables,
+    signature: AcpiSignature,
+    _length: usize,
+    phys_addr: PhysicalAddress
+) -> Result<(), &'static str> {
+    acpi_tables.add_table_location(signature, phys_addr, None)
+}
+
+
+/// The Windows ACPI Emulated devices Table (WAET) allows virtualized OSes
+/// to avoid workarounds for errata on physical devices.
+///
+/// <https://download.microsoft.com/download/7/E/7/7E7662CF-CBEA-470B-A97E-CE7CE0D98DC2/WAET.docx>
+#[repr(C, packed)]
+#[derive(Clone, Copy, Debug, FromBytes)]
+pub struct Waet {
+    pub header: Sdt,
+    pub emulated_device_flags: u32,
+}
+const _: () = assert!(core::mem::size_of::<Waet>() == 40);
+const _: () = assert!(core::mem::align_of::<Waet>() == 1);
+
+impl Waet {
+    /// Finds the WAET in the given `AcpiTables` and returns a reference to it.
+    pub fn get(acpi_tables: &AcpiTables) -> Option<&Waet> {
+        acpi_tables.table(WAET_SIGNATURE).ok()
+    }
+
+    /// Returns whether the RTC has been enhanced not to require
+    /// acknowledgment after it asserts an interrupt.
+    ///
+    /// If this returns `true`, an interrupt handler can bypass
+    /// reading the RTC register to unlatch the pending interrupt.
+    pub fn rtc_good(&self) -> bool {
+        const RTC_GOOD: u32 = 1 << 0;
+        self.emulated_device_flags & RTC_GOOD == RTC_GOOD
+    }
+
+    /// Returns whether the ACPI PM timer has been enhanced not to require
+    /// multiple reads.
+    ///
+    /// If this returns `true`, only a single read of the ACPI PM timer is
+    /// necessary to obtain a reliable value from it.
+    pub fn acpi_pm_timer_good(&self) -> bool {
+        const ACPI_PM_TIMER_GOOD: u32 = 1 << 1;
+        self.emulated_device_flags & ACPI_PM_TIMER_GOOD == ACPI_PM_TIMER_GOOD
+    }
+}