---
title: PCIe and USB Driver Model
url: https://doc.liz6.com/en/linux-kernel/10-drivers-and-device-model/02-pcie-and-usb-driver-model
locale: en
area: linux-kernel
tags:
- linux-kernel
- drivers-and-device-model
date: 2026-06-30
modified: 2026-07-16
description: 'Coverage: PCIe enumeration (BAR/MMIO/MSI) → pci_driver → USB protocol stack (URB/endpoint) → usb_driver → hotplug → power management Kernel version: 2.6 ~ 6.x'
---
# PCIe and USB Driver Model
> Coverage: PCIe enumeration (BAR/MMIO/MSI) → pci_driver → USB protocol stack (URB/endpoint) → usb_driver → hotplug → power management
> Kernel version: 2.6 ~ 6.x
## PCIe
### Bus Enumeration
### pci_dev
```c
// include/linux/pci.h
struct pci_dev {
struct pci_bus *bus; // Bus it belongs to
unsigned int devfn; // device + function
unsigned short vendor, device; // Matches pci_device_id
unsigned short subsystem_vendor, subsystem_device;
u32 class; // Device class (NVMe, VGA, USB, ...)
struct resource resource[6]; // BAR 0~5 (MMIO/IO address ranges)
unsigned int irq; // Interrupt number (may be a new number allocated after MSI)
struct pcie_link_state *link_state; // PCIe link (gen, width)
// DMA
u64 dma_mask; // Addressable range
struct device dev; // Embedded device (device model)
};
```
### pci_driver
```c
struct pci_driver {
const struct pci_device_id *id_table; // Match table
int (*probe)(struct pci_dev *, const struct pci_device_id *);
void (*remove)(struct pci_dev *);
int (*suspend)(struct pci_dev *, pm_message_t);
int (*resume)(struct pci_dev *);
struct device_driver driver; // Embedded driver (registered to PCI bus)
};
// Registration: pci_register_driver(&mydrv)
// Binding: PCI bus enumeration → match vendor:device → probe()
```
### MSI/MSI-X
```c
// Message-based interrupts replacing INTx line interrupts:
// MSI: Single vector or a small number of vectors
// MSI-X: Up to 2048 independent vectors
// Allocation:
int nvec = pci_alloc_irq_vectors(pdev, 1, 16, PCI_IRQ_MSIX);
// → 16 MSI-X vectors → pci_irq_vector(pdev, i) to get Linux IRQ number
// Each vector has independent affinity → can be bound to different CPUs
// NVMe: One MSI-X per IO queue → parallel interrupt processing
```
---
## USB
### USB Protocol Stack
```c
// drivers/usb/core/
// Layered architecture:
// USB Core (usbcore): Protocol implementation, URB management
// Host Controller Driver (HCD): xHCI, EHCI, OHCI
// Device Driver: usb_driver (e.g., usb-storage, usbhid)
// Descriptor hierarchy for USB devices:
// Device Descriptor → Config Descriptor → Interface Descriptor → Endpoint Descriptor
// One USB device: 1 device, N configs, M interfaces, K endpoints
// Endpoint types:
// Control: setup packet (configuration commands)
// Bulk: Large data transfers (storage, printers)
// Interrupt: Periodic polling (HID: keyboard/mouse)
// Isochronous: Real-time streaming (audio/video, no retransmission)
```
### URB (USB Request Block)
```c
// include/linux/usb.h
struct urb {
struct usb_device *dev; // Target device
unsigned int pipe; // Encodes endpoint + direction
void *transfer_buffer;
u32 transfer_buffer_length;
int actual_length;
usb_complete_t complete; // Completion callback
int status; // Completion status (0=OK, -EPROTO, -ETIMEDOUT, ...)
int interval; // Polling interval for interrupt/isochronous transfers
};
```
### usb_driver
```c
struct usb_driver {
const struct usb_device_id *id_table; // VID/PID match
int (*probe)(struct usb_interface *, const struct usb_device_id *);
void (*disconnect)(struct usb_interface *);
struct device_driver drvwrap; // Embedded driver (registered to USB bus)
};
```
**Key**: The object passed to `probe` is `usb_interface`, not `usb_device`—because a USB device can have multiple interfaces (e.g., webcam: video interface + audio interface), and different interfaces can bind to different drivers.
---
## Hotplug
---
## References
- **Source Code**: `drivers/pci/`, `drivers/usb/core/`, `include/linux/pci.h`, `include/linux/usb.h`
- **Kernel Documentation**: `Documentation/PCI/`, `Documentation/driver-api/usb/`
- **LWN**: "The PCI subsystem", "USB in the Linux kernel"
*Keywords: PCIe, BAR, MSI-X, pci_driver, USB, URB, endpoint, usb_driver, hotplug, udev*