Add documentation to bus

kernel/comps/virtio/src/transport/mmio/device.rs

@@ -9,7 +9,7 @@ use log::warn;
 use ostd::{
     bus::mmio::{
         bus::MmioDevice,
-        device::{MmioCommonDevice, VirtioMmioVersion},
+        common_device::{MmioCommonDevice, VirtioMmioVersion},
     },
     io_mem::IoMem,
     mm::{DmaCoherent, PAGE_SIZE},
@@ -34,7 +34,7 @@ pub struct VirtioMmioDevice {
 pub struct VirtioMmioTransport {
     layout: SafePtr<VirtioMmioLayout, IoMem>,
     device: Arc<VirtioMmioDevice>,
-    common_device: ostd::bus::mmio::device::MmioCommonDevice,
+    common_device: ostd::bus::mmio::common_device::MmioCommonDevice,
     multiplex: Arc<RwLock<MultiplexIrq>>,
 }
 

kernel/comps/virtio/src/transport/mmio/driver.rs

@@ -6,7 +6,7 @@ use ostd::{
     bus::{
         mmio::{
             bus::{MmioDevice, MmioDriver},
-            device::MmioCommonDevice,
+            common_device::MmioCommonDevice,
         },
         BusProbeError,
     },

ostd/src/arch/x86/device/mod.rs

@@ -3,9 +3,6 @@
 //! Device-related APIs.
 //! This module mainly contains the APIs that should exposed to the device driver like PCI, RTC
 
-// FIXME: remove this lint when the documentation of this module is extensively added.
-#![allow(missing_docs)]
-
 pub mod cmos;
 pub mod io_port;
 pub mod serial;

ostd/src/bus/mmio/bus.rs

@@ -1,15 +1,19 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! MMIO bus.
+
 #![allow(unused_variables)]
 
 use alloc::{collections::VecDeque, fmt::Debug, sync::Arc, vec::Vec};
 
 use log::{debug, error};
 
-use super::device::MmioCommonDevice;
+use super::common_device::MmioCommonDevice;
 use crate::bus::BusProbeError;
 
+/// MMIO device trait
 pub trait MmioDevice: Sync + Send + Debug {
+    /// Device ID
     fn device_id(&self) -> u32;
 }
 
@@ -37,6 +41,7 @@ pub struct MmioBus {
 }
 
 impl MmioBus {
+    /// Registers a MMIO driver to the MMIO bus.
     pub fn register_driver(&mut self, driver: Arc<dyn MmioDriver>) {
         debug!("Register driver:{:#x?}", driver);
         let length = self.common_devices.len();

ostd/src/bus/mmio/common_device.rs

@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: MPL-2.0
+
+//! MMIO device common definitions or functions.
+
+use int_to_c_enum::TryFromInt;
+use log::info;
+
+use super::VIRTIO_MMIO_MAGIC;
+use crate::{
+    io_mem::IoMem,
+    mm::{paddr_to_vaddr, Paddr, VmIo},
+    trap::IrqLine,
+};
+
+/// MMIO Common device.
+#[derive(Debug)]
+pub struct MmioCommonDevice {
+    io_mem: IoMem,
+    irq: IrqLine,
+}
+
+impl MmioCommonDevice {
+    pub(super) fn new(paddr: Paddr, handle: IrqLine) -> Self {
+        // TODO: Implement universal access to MMIO devices since we are temporarily
+        // using specific virtio device as implementation of CommonDevice.
+
+        // Read magic value
+        // SAFETY: It only read the value and judge if the magic value fit 0x74726976
+        unsafe {
+            debug_assert_eq!(*(paddr_to_vaddr(paddr) as *const u32), VIRTIO_MMIO_MAGIC);
+        }
+        // SAFETY: This range is virtio-mmio device space.
+        let io_mem = unsafe { IoMem::new(paddr..paddr + 0x200) };
+        let res = Self {
+            io_mem,
+            irq: handle,
+        };
+        info!(
+            "[Virtio]: Found Virtio mmio device, device id:{:?}, irq number:{:?}",
+            res.device_id(),
+            res.irq.num()
+        );
+        res
+    }
+
+    /// Base address
+    pub fn address(&self) -> Paddr {
+        self.io_mem.paddr()
+    }
+
+    /// Grants access to the MMIO
+    pub fn io_mem(&self) -> &IoMem {
+        &self.io_mem
+    }
+
+    /// Device ID
+    pub fn device_id(&self) -> u32 {
+        self.io_mem.read_val::<u32>(8).unwrap()
+    }
+
+    /// Version of the MMIO device.
+    pub fn version(&self) -> VirtioMmioVersion {
+        VirtioMmioVersion::try_from(self.io_mem.read_val::<u32>(4).unwrap()).unwrap()
+    }
+
+    /// Interrupt line
+    pub fn irq(&self) -> &IrqLine {
+        &self.irq
+    }
+
+    /// Mutable Interrupt line
+    pub fn irq_mut(&mut self) -> &mut IrqLine {
+        &mut self.irq
+    }
+}
+
+/// Virtio MMIO version
+#[derive(Debug, Clone, Copy, TryFromInt, PartialEq, Eq, PartialOrd, Ord)]
+#[repr(u32)]
+pub enum VirtioMmioVersion {
+    /// Legacy
+    Legacy = 1,
+    /// Modern
+    Modern = 2,
+}

ostd/src/bus/mmio/device.rs

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! MMIO device common definitions or functions.
+
 use int_to_c_enum::TryFromInt;
 use log::info;
 
@@ -40,34 +42,45 @@ impl MmioCommonDevice {
         res
     }
 
+    /// Base address
     pub fn address(&self) -> Paddr {
         self.io_mem.paddr()
     }
 
+    /// Grants access to the MMIO
     pub fn io_mem(&self) -> &IoMem {
         &self.io_mem
     }
 
+    /// Device ID
     pub fn device_id(&self) -> u32 {
         self.io_mem.read_val::<u32>(8).unwrap()
     }
 
+    /// Version of the MMIO device.
+    ///
+    /// FIXME: This function can only used in Virtio-mmio devices.
     pub fn version(&self) -> VirtioMmioVersion {
         VirtioMmioVersion::try_from(self.io_mem.read_val::<u32>(4).unwrap()).unwrap()
     }
 
+    /// Interrupt line
     pub fn irq(&self) -> &IrqLine {
         &self.irq
     }
 
+    /// Mutable Interrupt line
     pub fn irq_mut(&mut self) -> &mut IrqLine {
         &mut self.irq
     }
 }
 
+/// Virtio MMIO version
 #[derive(Debug, Clone, Copy, TryFromInt, PartialEq, Eq, PartialOrd, Ord)]
 #[repr(u32)]
 pub enum VirtioMmioVersion {
+    /// Legacy
     Legacy = 1,
+    /// Modern
     Modern = 2,
 }

ostd/src/bus/mmio/mod.rs

@@ -5,7 +5,7 @@
 //! Virtio over MMIO
 
 pub mod bus;
-pub mod device;
+pub mod common_device;
 
 use alloc::vec::Vec;
 use core::ops::Range;
@@ -18,16 +18,17 @@ use self::bus::MmioBus;
 #[cfg(feature = "intel_tdx")]
 use crate::arch::tdx_guest;
 use crate::{
-    arch::kernel::IO_APIC, bus::mmio::device::MmioCommonDevice, mm::paddr_to_vaddr, sync::SpinLock,
-    trap::IrqLine,
+    arch::kernel::IO_APIC, bus::mmio::common_device::MmioCommonDevice, mm::paddr_to_vaddr,
+    sync::SpinLock, trap::IrqLine,
 };
 
 const VIRTIO_MMIO_MAGIC: u32 = 0x74726976;
 
+/// MMIO bus instance
 pub static MMIO_BUS: SpinLock<MmioBus> = SpinLock::new(MmioBus::new());
 static IRQS: SpinLock<Vec<IrqLine>> = SpinLock::new(Vec::new());
 
-pub fn init() {
+pub(crate) fn init() {
     #[cfg(feature = "intel_tdx")]
     // SAFETY:
     // This is safe because we are ensuring that the address range 0xFEB0_0000 to 0xFEB0_4000 is valid before this operation.

ostd/src/bus/mod.rs

@@ -2,9 +2,6 @@
 
 //! Bus operations
 
-// FIXME: remove this lint when the docs of the whole bus module are added.
-#![allow(missing_docs)]
-
 pub mod mmio;
 pub mod pci;
 
@@ -18,7 +15,7 @@ pub enum BusProbeError {
 }
 
 /// Initializes the bus
-pub fn init() {
+pub(crate) fn init() {
     pci::init();
     mmio::init();
 }

ostd/src/bus/pci/bus.rs

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! PCI bus
+
 #![allow(unused_variables)]
 
 use alloc::{collections::VecDeque, sync::Arc, vec::Vec};
@@ -10,7 +12,9 @@ use log::{debug, error};
 use super::{device_info::PciDeviceId, PciCommonDevice};
 use crate::bus::BusProbeError;
 
+/// PciDevice trait.
 pub trait PciDevice: Sync + Send + Debug {
+    /// Gets device id.
     fn device_id(&self) -> PciDeviceId;
 }
 
@@ -42,6 +46,7 @@ pub struct PciBus {
 }
 
 impl PciBus {
+    /// Registers a PCI driver to the PCI bus.
     pub fn register_driver(&mut self, driver: Arc<dyn PciDriver>) {
         debug!("Register driver:{:#x?}", driver);
         let length = self.common_devices.len();

ostd/src/bus/pci/capability/mod.rs

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! PCI device capabilities.
+
 #![allow(dead_code)]
 
 use alloc::vec::Vec;
@@ -14,6 +16,7 @@ use super::{
 pub mod msix;
 pub mod vendor;
 
+/// PCI Capability
 #[derive(Debug)]
 pub struct Capability {
     id: u8,
@@ -26,6 +29,7 @@ pub struct Capability {
     cap_data: CapabilityData,
 }
 
+/// PCI Capability data.
 #[derive(Debug, Clone)]
 pub enum CapabilityData {
     /// Id:0x01, Power Management
@@ -76,11 +80,12 @@ impl Capability {
     /// 0xFC, the top of the capability position.
     const CAPABILITY_TOP: u16 = 0xFC;
 
+    /// Gets the capability data
     pub fn capability_data(&self) -> &CapabilityData {
         &self.cap_data
     }
 
-    /// get the capabilities of one device
+    /// Gets the capabilities of one device
     pub(super) fn device_capabilities(dev: &mut PciCommonDevice) -> Vec<Self> {
         if !dev.status().contains(Status::CAPABILITIES_LIST) {
             return Vec::new();

ostd/src/bus/pci/capability/msix.rs

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! MSI-X capability support.
+
 #![allow(dead_code)]
 #![allow(unused_variables)]
 
@@ -150,11 +152,13 @@ impl CapabilityMsixData {
         }
     }
 
+    /// MSI-X Table size
     pub fn table_size(&self) -> u16 {
         // bit 10:0 table size
         (self.loc.read16(self.ptr + 2) & 0b11_1111_1111) + 1
     }
 
+    /// Enables an interrupt line, it will replace the old handle with the new handle.
     pub fn set_interrupt_vector(&mut self, handle: IrqLine, index: u16) {
         if index >= self.table_size {
             return;
@@ -174,6 +178,7 @@ impl CapabilityMsixData {
             .unwrap();
     }
 
+    /// Gets mutable IrqLine. User can register callbacks by using this function.
     pub fn irq_mut(&mut self, index: usize) -> Option<&mut IrqLine> {
         self.irqs[index].as_mut()
     }

ostd/src/bus/pci/capability/vendor.rs

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! Vendor-specific capability support.
+
 use crate::{
     bus::pci::{common_device::PciCommonDevice, device_info::PciDeviceLocation},
     Error, Result,
@@ -23,41 +25,45 @@ impl CapabilityVndrData {
         }
     }
 
+    /// The length of this capability
+    #[allow(clippy::len_without_is_empty)]
     pub fn len(&self) -> u16 {
         self.length
     }
 
-    pub fn is_empty(&self) -> bool {
-        self.length == 0
-    }
-
+    /// Reads u8 from the capability.
     pub fn read8(&self, offset: u16) -> Result<u8> {
         self.check_range(offset)?;
         Ok(self.location.read8(self.cap_ptr + offset))
     }
 
+    /// Writes u8 to the capability.
     pub fn write8(&self, offset: u16, value: u8) -> Result<()> {
         self.check_range(offset)?;
         self.location.write8(self.cap_ptr + offset, value);
         Ok(())
     }
 
+    /// Reads u16 from the capability.
     pub fn read16(&self, offset: u16) -> Result<u16> {
         self.check_range(offset)?;
         Ok(self.location.read16(self.cap_ptr + offset))
     }
 
+    /// Writes u16 to the capability.
     pub fn write16(&self, offset: u16, value: u16) -> Result<()> {
         self.check_range(offset)?;
         self.location.write16(self.cap_ptr + offset, value);
         Ok(())
     }
 
+    /// Reads u32 from the capability.
     pub fn read32(&self, offset: u16) -> Result<u32> {
         self.check_range(offset)?;
         Ok(self.location.read32(self.cap_ptr + offset))
     }
 
+    /// Writes u32 to the capability.
     pub fn write32(&self, offset: u16, value: u32) -> Result<()> {
         self.check_range(offset)?;
         self.location.write32(self.cap_ptr + offset, value);

ostd/src/bus/pci/cfg_space.rs

@@ -1,5 +1,9 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! The PCI configuration space.
+//!
+//! Reference: <https://wiki.osdev.org/PCI>
+
 use alloc::sync::Arc;
 use core::mem::size_of;
 
@@ -12,48 +16,87 @@ use crate::{
     Error, Result,
 };
 
+/// Offset in PCI device's common configuration space(Not the PCI bridge).
 #[repr(u16)]
 pub enum PciDeviceCommonCfgOffset {
+    /// Vendor ID
     VendorId = 0x00,
+    /// Device ID
     DeviceId = 0x02,
+    /// PCI Command
     Command = 0x04,
+    /// PCI Status
     Status = 0x06,
+    /// Revision ID
     RevisionId = 0x08,
+    /// Class code
     ClassCode = 0x09,
+    /// Cache Line Size
     CacheLineSize = 0x0C,
+    /// Latency Timer
     LatencyTimer = 0x0D,
+    /// Header Type: Identifies the layout of the header.
     HeaderType = 0x0E,
+    /// BIST: Represents the status and allows control of a devices BIST(built-in self test).
     Bist = 0x0F,
+    /// Base Address Register #0
     Bar0 = 0x10,
+    /// Base Address Register #1
     Bar1 = 0x14,
+    /// Base Address Register #2
     Bar2 = 0x18,
+    /// Base Address Register #3
     Bar3 = 0x1C,
+    /// Base Address Register #4
     Bar4 = 0x20,
+    /// Base Address Register #5
     Bar5 = 0x24,
+    /// Cardbus CIS Pointer
     CardbusCisPtr = 0x28,
+    /// Subsystem Vendor ID
     SubsystemVendorId = 0x2C,
+    /// Subsystem ID
     SubsystemId = 0x2E,
+    /// Expansion ROM base address
     XromBar = 0x30,
+    /// Capabilities pointer
     CapabilitiesPointer = 0x34,
+    /// Interrupt Line
     InterruptLine = 0x3C,
+    /// INterrupt PIN
     InterruptPin = 0x3D,
+    /// Min Grant
     MinGrant = 0x3E,
+    /// Max latency
     MaxLatency = 0x3F,
 }
 
 bitflags! {
     /// PCI device common config space command register.
     pub struct Command: u16 {
+        /// Sets to 1 if the device can respond to I/O Space accesses.
         const IO_SPACE                  =  1 << 0;
+        /// Sets to 1 if the device can respond to Memory SPace accesses.
         const MEMORY_SPACE              =  1 << 1;
+        /// Sets to 1 if the device can behave as a bus master.
         const BUS_MASTER                =  1 << 2;
+        /// Sets to 1 if the device can monitor Special Cycle operations.
         const SPECIAL_CYCLES            =  1 << 3;
+        /// Memory Write and Invalidate Enable. Set to 1 if the device can
+        /// generate the Memory Write and Invalidate command.
         const MWI_ENABLE                =  1 << 4;
+        /// Sets to 1 if the device does not respond to palette register writes
+        /// and will snoop the data.
         const VGA_PALETTE_SNOOP         =  1 << 5;
+        /// Sets to 1 if the device will takes its normal action when a parity
+        /// error is detected.
         const PARITY_ERROR_RESPONSE     =  1 << 6;
-        const STEPPING_CONTROL          =  1 << 7;
+        /// Sets to 1 if the SERR# driver is enabled.
         const SERR_ENABLE               =  1 << 8;
+        /// Sets to 1 if the device is allowed to generate fast back-to-back
+        /// transactions
         const FAST_BACK_TO_BACK_ENABLE  =  1 << 9;
+        /// Sets to 1 if the assertion of the devices INTx# signal is disabled.
         const INTERRUPT_DISABLE         =  1 << 10;
     }
 }
@@ -61,17 +104,45 @@ bitflags! {
 bitflags! {
     /// PCI device common config space status register.
     pub struct Status: u16 {
+        /// The status of the device's INTx# signal.
         const INTERRUPT_STATUS          = 1 << 3;
+        /// Sets to 1 if the device support capabilities.
         const CAPABILITIES_LIST         = 1 << 4;
+        /// Sets to 1 if the device is capable of running at 66 MHz.
         const MHZ66_CAPABLE             = 1 << 5;
+        /// Sets to 1 if the device can accpet fast back-to-back transactions
+        /// that are not from the same agent.
         const FAST_BACK_TO_BACK_CAPABLE = 1 << 7;
+        /// This bit is only set when the following conditions are met:
+        /// 1. The bus agent asserted PERR# on a read or observed an assertion
+        /// of PERR# on a write
+        /// 2. The agent setting the bit acted as the bus master for the
+        /// operation in which the error occurred
+        /// 3. Bit 6 of the Command register (Parity Error Response bit) is set
+        ///  to 1.
         const MASTER_DATA_PARITY_ERROR  = 1 << 8;
+        /// The read-only bit that represent the slowest time that a device will
+        /// assert DEVSEL# for any bus command except Configuration Space read
+        /// and writes.
+        ///
+        /// If both `DEVSEL_MEDIUM_TIMING` and `DEVSEL_SLOW_TIMING` are not set,
+        /// then it represents fast timing
         const DEVSEL_MEDIUM_TIMING      = 1 << 9;
+        /// Check `DEVSEL_MEDIUM_TIMING`
         const DEVSEL_SLOW_TIMING        = 1 << 10;
+        /// Sets to 1 when a target device terminates a transaction with Target-
+        /// Abort.
         const SIGNALED_TARGET_ABORT     = 1 << 11;
+        /// Sets to 1 by a master device when its transaction is terminated with
+        /// Target-Abort
         const RECEIVED_TARGET_ABORT     = 1 << 12;
+        /// Sets to 1 by a master device when its transcation (except for Special
+        /// Cycle transactions) is terminated with Master-Abort.
         const RECEIVED_MASTER_ABORT     = 1 << 13;
+        /// Sets to 1 when the device asserts SERR#
         const SIGNALED_SYSTEM_ERROR     = 1 << 14;
+        /// Sets to 1 when the device detects a parity error, even if parity error
+        /// handling is disabled.
         const DETECTED_PARITY_ERROR     = 1 << 15;
     }
 }
@@ -79,7 +150,9 @@ bitflags! {
 /// BAR space in PCI common config space.
 #[derive(Debug, Clone)]
 pub enum Bar {
+    /// Memory BAR
     Memory(Arc<MemoryBar>),
+    /// I/O BAR
     Io(Arc<IoBar>),
 }
 
@@ -103,12 +176,11 @@ impl Bar {
     }
 }
 
+/// Memory BAR
 #[derive(Debug, Clone)]
 pub struct MemoryBar {
     base: u64,
     size: u32,
-    /// Whether this bar is prefetchable, allowing the CPU to get the data
-    /// in advance.
     prefetchable: bool,
     address_length: AddrLen,
     io_memory: IoMem,
@@ -120,23 +192,28 @@ impl MemoryBar {
         self.address_length
     }
 
+    /// Whether this bar is prefetchable, allowing the CPU to get the data
+    /// in advance.
     pub fn prefetchable(&self) -> bool {
         self.prefetchable
     }
 
+    /// Base address
     pub fn base(&self) -> u64 {
         self.base
     }
 
+    /// Size of the memory
     pub fn size(&self) -> u32 {
         self.size
     }
 
+    /// Grants I/O memory access
     pub fn io_mem(&self) -> &IoMem {
         &self.io_memory
     }
 
-    /// Create a memory BAR structure.
+    /// Creates a memory BAR structure.
     fn new(location: &PciDeviceLocation, index: u8) -> Result<Self> {
         // Get the original value first, then write all 1 to the register to get the length
         let offset = index as u16 * 4 + PciDeviceCommonCfgOffset::Bar0 as u16;
@@ -175,10 +252,13 @@ impl MemoryBar {
 /// Whether this BAR is 64bit address or 32bit address
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum AddrLen {
+    /// 32 bits
     Bits32,
+    /// 64 bits
     Bits64,
 }
 
+/// I/O port BAR.
 #[derive(Debug, Clone, Copy)]
 pub struct IoBar {
     base: u32,
@@ -186,14 +266,17 @@ pub struct IoBar {
 }
 
 impl IoBar {
+    /// Base port
     pub fn base(&self) -> u32 {
         self.base
     }
 
+    /// Size of the port
     pub fn size(&self) -> u32 {
         self.size
     }
 
+    /// Reads from port
     pub fn read<T: PortRead>(&self, offset: u32) -> Result<T> {
         // Check alignment
         if (self.base + offset) % size_of::<T>() as u32 != 0 {
@@ -208,6 +291,7 @@ impl IoBar {
         unsafe { Ok(T::read_from_port((self.base + offset) as u16)) }
     }
 
+    /// Writes to port
     pub fn write<T: PortWrite>(&self, offset: u32, value: T) -> Result<()> {
         // Check alignment
         if (self.base + offset) % size_of::<T>() as u32 != 0 {

ostd/src/bus/pci/common_device.rs

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! PCI device common definitions or functions.
+
 #![allow(dead_code)]
 #![allow(unused_variables)]
 
@@ -21,22 +23,27 @@ pub struct PciCommonDevice {
 }
 
 impl PciCommonDevice {
+    /// PCI device ID
     pub fn device_id(&self) -> &PciDeviceId {
         &self.device_id
     }
 
+    /// PCI device location
     pub fn location(&self) -> &PciDeviceLocation {
         &self.location
     }
 
+    /// PCI Base Address Register (BAR) manager
     pub fn bar_manager(&self) -> &BarManager {
         &self.bar_manager
     }
 
+    /// PCI capabilities
     pub fn capabilities(&self) -> &Vec<Capability> {
         &self.capabilities
     }
 
+    /// Gets the PCI Command
     pub fn command(&self) -> Command {
         Command::from_bits_truncate(
             self.location
@@ -44,11 +51,13 @@ impl PciCommonDevice {
         )
     }
 
+    /// Sets the PCI Command
     pub fn set_command(&self, command: Command) {
         self.location
             .write16(PciDeviceCommonCfgOffset::Command as u16, command.bits())
     }
 
+    /// Gets the PCI status
     pub fn status(&self) -> Status {
         Status::from_bits_truncate(
             self.location
@@ -84,6 +93,7 @@ impl PciCommonDevice {
     }
 }
 
+/// Base Address Registers manager.
 #[derive(Debug)]
 pub struct BarManager {
     /// BARs, the bool indicate whether this bar should exposed to unprivileged part.

ostd/src/bus/pci/device_info.rs

@@ -1,19 +1,30 @@
 // SPDX-License-Identifier: MPL-2.0
 
+//! PCI device Information
+
 use core::iter;
 
 use super::cfg_space::PciDeviceCommonCfgOffset;
 use crate::arch::pci::{PCI_ADDRESS_PORT, PCI_DATA_PORT};
 
+/// PCI device ID
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub struct PciDeviceId {
+    /// Vendor ID
     pub vendor_id: u16,
+    /// Device ID
     pub device_id: u16,
+    /// Revision ID
     pub revision_id: u8,
+    /// Programming Interface Byte
     pub prog_if: u8,
+    /// Specifies the specific function the device performs.
     pub subclass: u8,
+    /// Specifies the type of function the device performs.
     pub class: u8,
+    /// Subsystem Vendor ID
     pub subsystem_vendor_id: u16,
+    /// Subsystem ID
     pub subsystem_id: u16,
 }
 
@@ -41,22 +52,24 @@ impl PciDeviceId {
     }
 }
 
+/// PCI device Location
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct PciDeviceLocation {
+    /// Bus number
     pub bus: u8,
-    /// Max 31
+    /// Device number with max 31
     pub device: u8,
-    /// Max 7
+    /// Deivce number with max 7
     pub function: u8,
 }
 
 impl PciDeviceLocation {
-    pub const MIN_BUS: u8 = 0;
-    pub const MAX_BUS: u8 = 255;
-    pub const MIN_DEVICE: u8 = 0;
-    pub const MAX_DEVICE: u8 = 31;
-    pub const MIN_FUNCTION: u8 = 0;
-    pub const MAX_FUNCTION: u8 = 7;
+    const MIN_BUS: u8 = 0;
+    const MAX_BUS: u8 = 255;
+    const MIN_DEVICE: u8 = 0;
+    const MAX_DEVICE: u8 = 31;
+    const MIN_FUNCTION: u8 = 0;
+    const MAX_FUNCTION: u8 = 7;
     /// By encoding bus, device, and function into u32, user can access a PCI device in x86 by passing in this value.
     #[inline(always)]
     pub fn encode_as_x86_address_value(self) -> u32 {

ostd/src/bus/pci/mod.rs

@@ -61,6 +61,7 @@ pub use device_info::{PciDeviceId, PciDeviceLocation};
 use self::{bus::PciBus, common_device::PciCommonDevice};
 use crate::sync::Mutex;
 
+/// PCI bus instance
 pub static PCI_BUS: Mutex<PciBus> = Mutex::new(PciBus::new());
 
 pub(crate) fn init() {