PCIe总线-Linux内核PCIe软件框架分析（十一）

1.简介

Linux内核PCIe软件框架如下图所示，按照PCIe的模式，可分为RC和EP软件框架。RC的软件框架分为五层，第一层为RC Controller Driver，和RC Controller硬件直接交互，不同的RC Controller，其驱动实现也不相同；第二层为Core层，该层将Controller进行了抽象，提供了统一的接口和数据结构，将所有的Controller管理起来，同时提供通用PCIe设备驱动注册和匹配接口，完成驱动和设备的绑定，管理所有PCIe设备；第三层为PCIe设备驱动层，包含了Storage、Ethernet、PCI桥等设备驱动；第四层为设备驱动层，根据设备类型，可分为字符设备驱动、网络设备驱动和块设备驱动。第五层为虚拟文件系统层，该层会在用户空间创建设备节点，提供了应用程序访问PCIe设备的路径。EP的软件框架分为六层，第一层为EP Controller Driver，和RC Controller Driver的功能相似；第二层为EP Controller Core层，该层向下将EP Controller进行了抽象，提供了统一的接口和数据结构，将所有的EP Controller管理起来；第三层为EP Function Core，该层统一管理EPF驱动和EPF设备，并提供两者相互匹配的方法；第四层为EP Configfs，在用户空间提供了配置和绑定EPF的接口，用户可以通过这些接口配置EPF，而无需修改驱动；第五层为EP Function Driver，和PCIe设备的具体功能相关；第六层为虚拟文件系统层，和RC的功能相同（EP也有设备驱动层，篇幅所限，图中未画出）。

2.RC软件框架

2.1.RC Controller Driver

RK3588 PCIe RC Controller Driver驱动定义如下所示。

MODULE_DEVICE_TABLE(of, rk_pcie_of_match);
static struct platform_driver rk_plat_pcie_driver = {.driver = {.name	= "rk-pcie",.of_match_table = rk_pcie_of_match,.suppress_bind_attrs = true,.pm = &rockchip_dw_pcie_pm_ops,},.probe = rk_pcie_probe,
};module_platform_driver(rk_plat_pcie_driver);

2.2.Core

2.2.1.Host Bridge

RC Core层使用struct pci_host_bridge数据结构描述Host Bridge。bus描述Root bus，其他bus都在该数据结构的链表中。ops和child_ops描述Root bus和其他bus上的设备的配置空间访问方法。windows链表保存bus-range和ranges的资源。dma_ranges链表保存dma-ranges的资源。使用pci_alloc_host_bridge和devm_pci_alloc_host_bridge函数分配struct pci_host_bridge数据结构，使用pci_free_host_bridge释放struct pci_host_bridge数据结构。pci_host_probe枚举Host Bridge下面所有PCIe设备。

[include/linux/pci.h]
struct pci_host_bridge {struct device	dev;struct pci_bus	*bus;		/* Root bus */struct pci_ops	*ops;       /* Low-level architecture-dependent routines */struct pci_ops	*child_ops;void		*sysdata;int		busnr;struct list_head windows;	 /* resource_entry */struct list_head dma_ranges; /* dma ranges resource list */......
};
struct pci_host_bridge *pci_alloc_host_bridge(size_t priv);
struct pci_host_bridge *devm_pci_alloc_host_bridge(struct device *dev,size_t priv);
void pci_free_host_bridge(struct pci_host_bridge *bridge);
int pci_host_probe(struct pci_host_bridge *bridge);

struct pci_ops描述访问PCIe设备配置空间的方法，需要RC Controller Driver实现。常用的是map_bus、read和write，map_bus用于映射访问配置空间的region，read和write用于读写配置空间。

[include/linux/pci.h]
struct pci_ops {int (*add_bus)(struct pci_bus *bus);void (*remove_bus)(struct pci_bus *bus);void __iomem *(*map_bus)(struct pci_bus *bus, unsigned int devfn, int where);int (*read)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 *val);int (*write)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 val);
};

2.2.2.Bus

RC Core层使用struct pci_bus数据结构描述PCIe bus。所有PCIe bus组成一个PCIe树型结构。parent指向Parent buses，children指向Child buses。devices链表保存该bus上的所有设备。number为该bus的总线编号，primary表示上游总线编号，busn_res保存桥下游总线编号范围，max_bus_speed表示该bus支持的最大速度，cur_bus_speed表示该bus当前的速度。pci_find_bus根据PCIe域和总线编号查找struct pci_bus，pci_add_new_bus创建一个struct pci_bus并添加到父总线上，注册Host Bridge时会自动创建bus0的数据结构，pci_bus_insert_busn_res和pci_bus_update_busn_res_end更新PCIe bus编号资源。

[include/linux/pci.h]
struct pci_bus {struct list_head node;		/* Node in list of buses */struct pci_bus	*parent;	/* Parent bus this bridge is on */struct list_head children;	/* List of child buses */struct list_head devices;	/* List of devices on this bus */struct pci_dev	*self;		/* Bridge device as seen by parent */struct list_head slots;		/* List of slots on this bus;protected by pci_slot_mutex */struct resource *resource[PCI_BRIDGE_RESOURCE_NUM];struct list_head resources;	/* Address space routed to this bus */struct resource busn_res;	/* Bus numbers routed to this bus */struct pci_ops	*ops;		/* Configuration access functions */struct msi_controller *msi;	/* MSI controller */void		*sysdata;	/* Hook for sys-specific extension */struct proc_dir_entry *procdir;	/* Directory entry in /proc/bus/pci */unsigned char	number;		/* Bus number */unsigned char	primary;	/* Number of primary bridge */unsigned char	max_bus_speed;	/* enum pci_bus_speed */unsigned char	cur_bus_speed;	/* enum pci_bus_speed */......
};struct pci_bus *pci_find_bus(int domain, int busnr);
struct pci_bus *pci_add_new_bus(struct pci_bus *parent,struct pci_dev *dev, int busnr);
void pci_remove_bus(struct pci_bus *bus);int pci_bus_insert_busn_res(struct pci_bus *b, int bus, int busmax);
int pci_bus_update_busn_res_end(struct pci_bus *b, int busmax);

2.2.3.Device

RC Core层使用struct pci_dev数据结构描述PCIe Devices。devfn表述device和function编号，vendor、device等保存PCIe设备配置空间头信息，driver指向该设备使用的驱动。resource保存设备的资源，如BAR、ROMs等。PCIe bus也是一个PCIe设备。pci_alloc_dev分配struct pci_dev数据结构，pci_dev_put释放struct pci_dev数据结构，pci_device_add向总线上添加PCIe设备。pci_bus_add_devices和pci_bus_add_device匹配PCIe设备和PCIe驱动。

[include/linux/pci.h]
/* The pci_dev structure describes PCI devices */
struct pci_dev {struct list_head bus_list;	/* Node in per-bus list */struct pci_bus	*bus;		/* Bus this device is on */struct pci_bus	*subordinate;	/* Bus this device bridges to */void		*sysdata;	/* Hook for sys-specific extension */struct proc_dir_entry *procent;	/* Device entry in /proc/bus/pci */struct pci_slot	*slot;		/* Physical slot this device is in */unsigned int	devfn;		/* Encoded device & function index */unsigned short	vendor;unsigned short	device;unsigned short	subsystem_vendor;unsigned short	subsystem_device;unsigned int	class;		/* 3 bytes: (base,sub,prog-if) */......struct pci_driver *driver;	/* Driver bound to this device */......int		cfg_size;		/* Size of config space *//** Instead of touching interrupt line and base address registers* directly, use the values stored here. They might be different!*/unsigned int	irq;struct resource resource[DEVICE_COUNT_RESOURCE]; /* I/O and memory regions + expansion ROMs */bool		match_driver;		/* Skip attaching driver */......
};struct pci_dev *pci_alloc_dev(struct pci_bus *bus);
void pci_dev_put(struct pci_dev *dev);
void pci_device_add(struct pci_dev *dev, struct pci_bus *bus);
void pci_bus_add_device(struct pci_dev *dev);
void pci_bus_add_devices(const struct pci_bus *bus);

2.2.4.Driver

RC Core层使用struct pci_driver数据结构描述PCIe设备驱动。PCIe设备和驱动匹配的信息保存到id_table中。pci_register_driver注册PCIe设备驱动，pci_unregister_driver注销PCIe设备驱动。

[include/linux/pci.h]
struct pci_driver {struct list_head	node;const char		*name;/* Must be non-NULL for probe to be called */const struct pci_device_id *id_table;/* New device inserted */int  (*probe)(struct pci_dev *dev, const struct pci_device_id *id);/* Device removed (NULL if not a hot-plug capable driver) */void (*remove)(struct pci_dev *dev);/* Device suspended */int  (*suspend)(struct pci_dev *dev, pm_message_t state);/* Device woken up */int  (*resume)(struct pci_dev *dev);void (*shutdown)(struct pci_dev *dev);/* On PF */int  (*sriov_configure)(struct pci_dev *dev, int num_vfs);/*  */const struct pci_error_handlers *err_handler;......
};
/* pci_register_driver() must be a macro so KBUILD_MODNAME can be expanded */
#define pci_register_driver(driver)		\__pci_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)void pci_unregister_driver(struct pci_driver *dev);

pci_bus_type用于匹配PCIe设备和驱动。

struct bus_type pci_bus_type = {.name		= "pci",.match		= pci_bus_match,.uevent		= pci_uevent,.probe		= pci_device_probe,.remove		= pci_device_remove,.shutdown	= pci_device_shutdown,.dev_groups	= pci_dev_groups,.bus_groups	= pci_bus_groups,.drv_groups	= pci_drv_groups,.pm		= PCI_PM_OPS_PTR,.num_vf		= pci_bus_num_vf,.dma_configure	= pci_dma_configure,
};

2.2.5.设备驱动

不同的PCIe设备，需要不同的PCIe设备驱动。下面列出PCIe桥和NVMe硬盘驱动。

2.2.5.1.桥驱动

如下所示，PCIe桥使用"pcieport"驱动。

[drivers/pci/pcie/portdrv_pci.c]
static const struct pci_device_id port_pci_ids[] = {/* handle any PCI-Express port */{ PCI_DEVICE_CLASS(((PCI_CLASS_BRIDGE_PCI << 8) | 0x00), ~0) },/* subtractive decode PCI-to-PCI bridge, class type is 060401h */{ PCI_DEVICE_CLASS(((PCI_CLASS_BRIDGE_PCI << 8) | 0x01), ~0) },/* handle any Root Complex Event Collector */{ PCI_DEVICE_CLASS(((PCI_CLASS_SYSTEM_RCEC << 8) | 0x00), ~0) },{ },
};
static struct pci_driver pcie_portdriver = {.name		= "pcieport",.id_table	= &port_pci_ids[0],.probe		= pcie_portdrv_probe,.remove		= pcie_portdrv_remove,.shutdown	= pcie_portdrv_remove,.err_handler	= &pcie_portdrv_err_handler,.driver.pm	= PCIE_PORTDRV_PM_OPS,
};
static int __init pcie_portdrv_init(void)
{if (pcie_ports_disabled)return -EACCES;pcie_init_services();dmi_check_system(pcie_portdrv_dmi_table);return pci_register_driver(&pcie_portdriver);
}
device_initcall(pcie_portdrv_init);

2.2.5.2.NVMe驱动

M.2 NVMe硬盘使用下面的驱动。

[drivers/nvme/host/pci.c]
static struct pci_driver nvme_driver = {.name		= "nvme",.id_table	= nvme_id_table,.probe		= nvme_probe,.remove		= nvme_remove,.shutdown	= nvme_shutdown,
#ifdef CONFIG_PM_SLEEP.driver		= {.pm	= &nvme_dev_pm_ops,},
#endif.sriov_configure = pci_sriov_configure_simple,.err_handler	= &nvme_err_handler,
};static int __init nvme_init(void)
{BUILD_BUG_ON(sizeof(struct nvme_create_cq) != 64);BUILD_BUG_ON(sizeof(struct nvme_create_sq) != 64);BUILD_BUG_ON(sizeof(struct nvme_delete_queue) != 64);BUILD_BUG_ON(IRQ_AFFINITY_MAX_SETS < 2);return pci_register_driver(&nvme_driver);
}
module_init(nvme_init);
module_exit(nvme_exit);

3.EP软件框架

3.1.EP Controller Driver

RK3399 PCIe EP Controller Driverr驱动定义如下所示。

[drivers/pci/controller/pcie-rockchip-ep.c]
static const struct of_device_id rockchip_pcie_ep_of_match[] = {{ .compatible = "rockchip,rk3399-pcie-ep"},{},
};static struct platform_driver rockchip_pcie_ep_driver = {.driver = {.name = "rockchip-pcie-ep",.of_match_table = rockchip_pcie_ep_of_match,},.probe = rockchip_pcie_ep_probe,
};builtin_platform_driver(rockchip_pcie_ep_driver);

3.2.EP Controller Core

3.2.1.EPC Device

EP Controller Core层使用struct pci_epc描述PCIe Endpoint Controller Device。EPC的所有的functions都挂到pci_epf链表上，ops指向了EPC提供的回调函数集合，用于设置EPC的配置空间、设置region、设置和发送中断等，windows保存了EPC的Outbound的地址段，num_windows表示Outbound的地址段的数量，max_functions保存了functions的最大数量。使用pci_epc_create和devm_pci_epc_create函数创建struct pci_epc，devm_pci_epc_destroy和pci_epc_destroy销毁struct pci_epc。

[include/linux/pci-epc.h]
/* struct pci_epc - represents the PCI EPC device */
struct pci_epc {struct device			dev;struct list_head		pci_epf;const struct pci_epc_ops	*ops;struct pci_epc_mem		**windows;struct pci_epc_mem		*mem;unsigned int			num_windows;u8				max_functions;struct config_group		*group;/* mutex to protect against concurrent access of EP controller */struct mutex			lock;unsigned long			function_num_map;struct atomic_notifier_head	notifier;
};#define pci_epc_create(dev, ops)    \__pci_epc_create((dev), (ops), THIS_MODULE)
#define devm_pci_epc_create(dev, ops)    \__devm_pci_epc_create((dev), (ops), THIS_MODULE)
void devm_pci_epc_destroy(struct device *dev, struct pci_epc *epc);
void pci_epc_destroy(struct pci_epc *epc);

struct pci_epc_ops如下图所示，这些回调函数很重要，EP Controller Driver必须实现。EPF驱动会调用这些函数配置EPC。

[include/linux/pci-epc.h]
struct pci_epc_ops {int	(*write_header)(struct pci_epc *epc, u8 func_no,struct pci_epf_header *hdr);int	(*set_bar)(struct pci_epc *epc, u8 func_no,struct pci_epf_bar *epf_bar);void	(*clear_bar)(struct pci_epc *epc, u8 func_no,struct pci_epf_bar *epf_bar);int	(*map_addr)(struct pci_epc *epc, u8 func_no,phys_addr_t addr, u64 pci_addr, size_t size);void	(*unmap_addr)(struct pci_epc *epc, u8 func_no,phys_addr_t addr);int	(*set_msi)(struct pci_epc *epc, u8 func_no, u8 interrupts);int	(*get_msi)(struct pci_epc *epc, u8 func_no);int	(*set_msix)(struct pci_epc *epc, u8 func_no, u16 interrupts,enum pci_barno, u32 offset);int	(*get_msix)(struct pci_epc *epc, u8 func_no);int	(*raise_irq)(struct pci_epc *epc, u8 func_no,enum pci_epc_irq_type type, u16 interrupt_num);int	(*start)(struct pci_epc *epc);void	(*stop)(struct pci_epc *epc);const struct pci_epc_features* (*get_features)(struct pci_epc *epc,u8 func_no);struct module *owner;
};

3.2.2.EPF绑定EPC

每个EP的Function都对应一个struct pci_epf设备，即EPF设备，EPF设备和EPC通过pci_epc_add_epf绑定，通过pci_epc_remove_epf解除绑定。

[include/linux/pci-epc.h]
int pci_epc_add_epf(struct pci_epc *epc, struct pci_epf *epf);
void pci_epc_remove_epf(struct pci_epc *epc, struct pci_epf *epf);

3.2.3.EPC API

下面的接口是对struct pci_epc_ops封装，供EPF驱动调用。

[include/linux/pci-epc.h]
int pci_epc_write_header(struct pci_epc *epc, u8 func_no,struct pci_epf_header *hdr);
int pci_epc_set_bar(struct pci_epc *epc, u8 func_no,struct pci_epf_bar *epf_bar);
void pci_epc_clear_bar(struct pci_epc *epc, u8 func_no,struct pci_epf_bar *epf_bar);
int pci_epc_map_addr(struct pci_epc *epc, u8 func_no,phys_addr_t phys_addr,u64 pci_addr, size_t size);
void pci_epc_unmap_addr(struct pci_epc *epc, u8 func_no,phys_addr_t phys_addr);
int pci_epc_set_msi(struct pci_epc *epc, u8 func_no, u8 interrupts);
int pci_epc_get_msi(struct pci_epc *epc, u8 func_no);
int pci_epc_set_msix(struct pci_epc *epc, u8 func_no, u16 interrupts,enum pci_barno, u32 offset);
int pci_epc_get_msix(struct pci_epc *epc, u8 func_no);
int pci_epc_raise_irq(struct pci_epc *epc, u8 func_no,enum pci_epc_irq_type type, u16 interrupt_num);
int pci_epc_start(struct pci_epc *epc);
void pci_epc_stop(struct pci_epc *epc);
const struct pci_epc_features *pci_epc_get_features(struct pci_epc *epc,u8 func_no);

3.3.EP Function Core

EP Function Core层定义了EPF Driver和EPF Device的数据结构，并提供注册、创建及绑定接口。

3.3.1.EPF Driver

EPF Driver的数据结构为struct pci_epf_driver。当EPF Device和EPC Device绑定后，会回调ops函数以通知EPF Driver，id_table定义EPF Driver和EPF Device匹配的信息。pci_epf_register_driver注册EPF Driver，pci_epf_unregister_driver注销EPF Driver。

[include/linux/pci-epf.h]
struct pci_epf_driver {int	(*probe)(struct pci_epf *epf);int	(*remove)(struct pci_epf *epf);struct device_driver	driver;struct pci_epf_ops	*ops;struct module		*owner;struct list_head	epf_group;const struct pci_epf_device_id	*id_table;
};
struct pci_epf_ops {int	(*bind)(struct pci_epf *epf);void	(*unbind)(struct pci_epf *epf);
};#define pci_epf_register_driver(driver)    \__pci_epf_register_driver((driver), THIS_MODULE)
void pci_epf_unregister_driver(struct pci_epf_driver *driver);

3.3.2.EPF Device

每个EP Function都对应一个EPF Device。EPF Device的数据结构为struct pci_epf_driver。header保存了该EP Function配置空间头信息，bar[6]保存了6个BAR映射的物理地址，msi_interrupts和msix_interrupts分别表示EP Function需要的中断数量，func_no表述EP Function的编号。pci_epf_create和pci_epf_destroy创建和销毁EPF Device。

[include/linux/pci-epf.h]
struct pci_epf {struct device		dev;const char		*name;struct pci_epf_header	*header;struct pci_epf_bar	bar[6];u8			msi_interrupts;u16			msix_interrupts;u8			func_no;struct pci_epc		*epc;struct pci_epf_driver	*driver;struct list_head	list;struct notifier_block   nb;/* mutex to protect against concurrent access of pci_epf_ops */struct mutex		lock;
};
struct pci_epf *pci_epf_create(const char *name);
void pci_epf_destroy(struct pci_epf *epf);

3.3.3.EPF Device匹配EPF Driver

pci_epf_bus_type用于匹配EPF Device和EPF Driver。

[drivers/pci/endpoint/pci-epf-core.c]
static struct bus_type pci_epf_bus_type = {.name		= "pci-epf",.match		= pci_epf_device_match,.probe		= pci_epf_device_probe,.remove		= pci_epf_device_remove,
};

3.4.EP Configfs

EP Configfs会在/sys目录下创建文件节点，使用者可以在用户空间通过这些文件节点，配置和创建EPP Device，绑定EPP Device、EPP Driver及EPC Device。

3.5.EP Function Driver。

下面是pci_epf_test的EP Function Driver。

[drivers/pci/endpoint/functions/pci-epf-test.c]
static struct pci_epf_ops ops = {.unbind	= pci_epf_test_unbind,.bind	= pci_epf_test_bind,
};static struct pci_epf_driver test_driver = {.driver.name	= "pci_epf_test",.probe		= pci_epf_test_probe,.id_table	= pci_epf_test_ids,.ops		= &ops,.owner		= THIS_MODULE,
};

参考资料

1. PCIEXPRESS体系结构导读
2. PCI Express technology 3.0
3. PCI Express® Base Specification Revision 5.0 Version 1.0
4. Rockchip RK3588 TRM
5. Linux kernel 5.10