AMD Xilinx PCIe Host 配置空间访问流程

hankfu

发布于 2024-08-20 09:08:51

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发布于 2024-08-20 09:08:51

文章被收录于专栏：hank

AMD Xilinx的Versal器件中的PCIe IP，也可以作为PCIe Host。 AR76647 提供了相关驱动。 Xilinx Linux PL PCIe Root Port 提供了配置和测试过程。

最近研究了Linux下，AMD Xilinx PCIe Host 配置空间访问流程。

pci_read_config_xxx 和 pci_write_config_xxx 函数定义

首先，Linux通用的PCI代码，需要PCI配置空间的访问函数 pci_read_config_xxx 和 pci_write_config_xxx。文件include\linux\Pci.h中对它们进行了声明。

int pci_read_config_byte(const struct pci_dev *dev, int where, u8 *val);
int pci_read_config_word(const struct pci_dev *dev, int where, u16 *val);
int pci_read_config_dword(const struct pci_dev *dev, int where, u32 *val);
int pci_write_config_byte(const struct pci_dev *dev, int where, u8 val);
int pci_write_config_word(const struct pci_dev *dev, int where, u16 val);
int pci_write_config_dword(const struct pci_dev *dev, int where, u32 val);

文件drivers\pci\Access.c中，通过调用pci_bus_read_config_xxx 和 pci_bus_write_config_xxx，定义了上述函数。

int pci_read_config_byte(const struct pci_dev *dev, int where, u8 *val)
{
	if (pci_dev_is_disconnected(dev)) {
		*val = ~0;
		return PCIBIOS_DEVICE_NOT_FOUND;
	}
	return pci_bus_read_config_byte(dev->bus, dev->devfn, where, val);
}
EXPORT_SYMBOL(pci_read_config_byte);

int pci_read_config_word(const struct pci_dev *dev, int where, u16 *val)
{
	if (pci_dev_is_disconnected(dev)) {
		*val = ~0;
		return PCIBIOS_DEVICE_NOT_FOUND;
	}
	return pci_bus_read_config_word(dev->bus, dev->devfn, where, val);
}
EXPORT_SYMBOL(pci_read_config_word);

int pci_read_config_dword(const struct pci_dev *dev, int where,
					u32 *val)
{
	if (pci_dev_is_disconnected(dev)) {
		*val = ~0;
		return PCIBIOS_DEVICE_NOT_FOUND;
	}
	return pci_bus_read_config_dword(dev->bus, dev->devfn, where, val);
}
EXPORT_SYMBOL(pci_read_config_dword);

int pci_write_config_byte(const struct pci_dev *dev, int where, u8 val)
{
	if (pci_dev_is_disconnected(dev))
		return PCIBIOS_DEVICE_NOT_FOUND;
	return pci_bus_write_config_byte(dev->bus, dev->devfn, where, val);
}
EXPORT_SYMBOL(pci_write_config_byte);

int pci_write_config_word(const struct pci_dev *dev, int where, u16 val)
{
	if (pci_dev_is_disconnected(dev))
		return PCIBIOS_DEVICE_NOT_FOUND;
	return pci_bus_write_config_word(dev->bus, dev->devfn, where, val);
}
EXPORT_SYMBOL(pci_write_config_word);

int pci_write_config_dword(const struct pci_dev *dev, int where,
					 u32 val)
{
	if (pci_dev_is_disconnected(dev))
		return PCIBIOS_DEVICE_NOT_FOUND;
	return pci_bus_write_config_dword(dev->bus, dev->devfn, where, val);
}
EXPORT_SYMBOL(pci_write_config_dword);

pci_bus_read_config_xxx 和 pci_bus_write_config_xxx 函数定义

pci_bus_read_config_xxx 和 pci_bus_write_config_xxx是更底层的函数。它们也在文件include\linux\Pci.h中被声明。

int pci_bus_read_config_byte(struct pci_bus *bus, unsigned int devfn,
			     int where, u8 *val);
int pci_bus_read_config_word(struct pci_bus *bus, unsigned int devfn,
			     int where, u16 *val);
int pci_bus_read_config_dword(struct pci_bus *bus, unsigned int devfn,
			      int where, u32 *val);
int pci_bus_write_config_byte(struct pci_bus *bus, unsigned int devfn,
			      int where, u8 val);
int pci_bus_write_config_word(struct pci_bus *bus, unsigned int devfn,
			      int where, u16 val);
int pci_bus_write_config_dword(struct pci_bus *bus, unsigned int devfn,
			       int where, u32 val);

pci_bus_read_config_xxx 和 pci_bus_write_config_xxx的代码通过宏“PCI_OP_READ”和宏“PCI_OP_WRITE”实现。

#define PCI_OP_READ(size, type, len) \
int noinline pci_bus_read_config_##size \
	(struct pci_bus *bus, unsigned int devfn, int pos, type *value)	\
{									\
	int res;							\
	unsigned long flags;						\
	u32 data = 0;							\
	if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;	\
	pci_lock_config(flags);						\
	res = bus->ops->read(bus, devfn, pos, len, &data);		\
	*value = (type)data;						\
	pci_unlock_config(flags);					\
	return res;							\
}

#define PCI_OP_WRITE(size, type, len) \
int noinline pci_bus_write_config_##size \
	(struct pci_bus *bus, unsigned int devfn, int pos, type value)	\
{									\
	int res;							\
	unsigned long flags;						\
	if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;	\
	pci_lock_config(flags);						\
	res = bus->ops->write(bus, devfn, pos, len, value);		\
	pci_unlock_config(flags);					\
	return res;							\
}

通过调用宏“PCI_OP_READ”和宏“PCI_OP_WRITE”，定义了pci_bus_read_config_xxx 和 pci_bus_write_config_xxx。

PCI_OP_READ(byte, u8, 1)
PCI_OP_READ(word, u16, 2)
PCI_OP_READ(dword, u32, 4)
PCI_OP_WRITE(byte, u8, 1)
PCI_OP_WRITE(word, u16, 2)
PCI_OP_WRITE(dword, u32, 4)

EXPORT_SYMBOL(pci_bus_read_config_byte);
EXPORT_SYMBOL(pci_bus_read_config_word);
EXPORT_SYMBOL(pci_bus_read_config_dword);
EXPORT_SYMBOL(pci_bus_write_config_byte);
EXPORT_SYMBOL(pci_bus_write_config_word);
EXPORT_SYMBOL(pci_bus_write_config_dword);

通过宏“PCI_OP_READ”和宏“PCI_OP_WRITE”，也可以看出，实现pci_bus_read_config_xxx 和 pci_bus_write_config_xxx，需要数据结构“struct pci_bus”中嵌套的数据结构“struct pci_ops”中的函数read和write函数。

/* Low-level architecture-dependent routines */
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);
};

pcie-xdma-pl.c 中的pci_ops

pcie-xdma-pl.c定义了pci_ops。

/* PCIe operations */
static struct pci_ops xilinx_pcie_ops = {
	.map_bus = xilinx_pcie_map_bus,
	.read	= pci_generic_config_read,
	.write	= pci_generic_config_write,
};

pci_generic_config_read和pci_generic_config_write在drivers\pci\access.c中定义。

int pci_generic_config_read(struct pci_bus *bus, unsigned int devfn,
			    int where, int size, u32 *val)
{
	void __iomem *addr;

	addr = bus->ops->map_bus(bus, devfn, where);
	if (!addr) {
		*val = ~0;
		return PCIBIOS_DEVICE_NOT_FOUND;
	}

	if (size == 1)
		*val = readb(addr);
	else if (size == 2)
		*val = readw(addr);
	else
		*val = readl(addr);

	return PCIBIOS_SUCCESSFUL;
}
EXPORT_SYMBOL_GPL(pci_generic_config_read);

int pci_generic_config_write(struct pci_bus *bus, unsigned int devfn,
			     int where, int size, u32 val)
{
	void __iomem *addr;

	addr = bus->ops->map_bus(bus, devfn, where);
	if (!addr)
		return PCIBIOS_DEVICE_NOT_FOUND;

	if (size == 1)
		writeb(val, addr);
	else if (size == 2)
		writew(val, addr);
	else
		writel(val, addr);

	return PCIBIOS_SUCCESSFUL;
}
EXPORT_SYMBOL_GPL(pci_generic_config_write);

可以看到，它们调用了“struct pci_bus *bus”中的map_bus（）函数。

pcie-xdma-pl.c 也实现了 map_bus（）函数。它根据总线号、设备号，得到一个寄存器地址。通过这个寄存器地址操作，就能对设备的发起配置寄存器的读写操作。

static void __iomem *xilinx_pcie_map_bus(struct pci_bus *bus,
					 unsigned int devfn, int where)
{
	struct xilinx_pcie_port *port = bus->sysdata;
	int relbus;

	if (!xilinx_pcie_valid_device(bus, devfn))
		return NULL;

	relbus = (bus->number << ECAM_BUS_NUM_SHIFT) |
		 (devfn << ECAM_DEV_NUM_SHIFT);

	return port->reg_base + relbus + where;
}

这样，PCIe Host 配置空间访问流程中，与设备相关的代码就齐全了。