pcie读取配置空间bar空间的size

pcie开始通过配置空间来读取pcie基本信息，改信息通过上层lspci能够正常解析，客户反馈自己的xilinx设备bar0只有512k，需要我们确定一下，遂确定如下

type0和type1


For device Functions with Type 0 headers (all types of Endpoints)
For device Functions with Type 1 headers (Root Ports, Switches and Bridges)

所有的ep设备都是type0 headers
所有的rc设备,switch,bridge都是type1 headers

type0/1 headers的标志位

如何查看设备是type0还是type1 headers，可以通过配置空间的0x1e的值来确定，如下


For Functions that implement a Type 0 Configuration Space 
header the encoding 000 0000b must be used.
For Functions that implement a Type 1 Configuration Space 
header the encoding 000 0001b must be used

也就是说，对于0x0e的值，如果是0x1则是type1 headers型设备，通常是rc或bridges，如果是0x0则是type0 headers型设备，通常是ep。

lspci读取type0/1


root@kylin:~# lspci -x
00:00.0 PCI bridge: Fuzhou Rockchip Electronics Co., Ltd Device 3588 (rev 01)
00: 87 1d 88 35 07 05 10 00 01 00 04 06 00 00 01 00
10: 00 00 00 00 00 00 00 00 00 01 ff 00 f0 00 00 00
20: 00 f0 00 f0 f1 ff 01 00 00 00 00 00 00 00 00 00
30: 00 00 00 00 40 00 00 00 00 00 00 00 70 01 02 00

01:00.0 Memory controller: Xilinx Corporation Device 7014
00: ee 10 14 70 00 00 10 00 00 00 80 05 00 00 00 00
10: 00 00 f8 ff 00 00 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 ee 10 07 00
30: 00 00 00 00 80 00 00 00 00 00 00 00 00 01 00 00

lspci -x可以读到0xe的值，这里可以看到00:00.0 是type1 headers，而01:00.0则是type0 headers

type0/1的配置空间

通常的配置空间布局如下图所示

type0的配置空间布局如下图所示

type1的配置空间布局如下图所示

这里可以知道，无论哪种type设备，bar0的寄存器都在0x10处，这里聚焦0x10处的信息

bar0的地址

对于0x10的值，默认是linux设置的映射地址，用作pcie域的读写操作。如下可以确定


root@kylin:~# lspci -x -s 01:00.0
01:00.0 Memory controller: Xilinx Corporation Device 7014
00: ee 10 14 70 00 00 10 00 00 00 80 05 00 00 00 00
10: 00 00 00 f0 00 00 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 ee 10 07 00
30: 00 00 00 00 80 00 00 00 00 00 00 00 ff 01 00 00

这里可以知道0x10的值为f0000000，这个0xf0000000是linux内通过设备树映射的可访问的地址。

bar0的大小

通过lspci读取

对于bar0的大小lspci已经读取出来了是512k，如下


root@kylin:~# lspci -s 01:00.0 -v
01:00.0 Memory controller: Xilinx Corporation Device 7014
	Subsystem: Xilinx Corporation Device 0007
	Flags: fast devsel, IRQ 255
	Memory at f0200000 (32-bit, non-prefetchable) [disabled] [size=512K]
	Capabilities: [80] Power Management version 3
	Capabilities: [90] MSI: Enable- Count=1/1 Maskable- 64bit+
	Capabilities: [c0] Express Endpoint, MSI 00
	Capabilities: [100] Advanced Error Reporting
lspci: Unable to load libkmod resources: error -2

通过setpci读取


setpci --dumpregs
setpci -s 01:00.0 0x10.L=0xffffffff
root@kylin:~# lspci -s 01:00.0 -x
01:00.0 Memory controller: Xilinx Corporation Device 7014
00: ee 10 14 70 00 00 10 00 00 00 80 05 00 00 00 00
10: 00 00 f8 ff 00 00 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 ee 10 07 00
30: 00 00 00 00 80 00 00 00 00 00 00 00 ff 01 00 00

这时候读出来是0xfff80000，取最低有效位0x80000，则正好是512k

通过io命令获取


io -4 0xf0000000 -r -l 64
io -4 -w 0xf0000010 0xffffffff
io -4 0xf0000010 -r

这里读出来仍是0xfff80000,换算也是512k

内核代码

内核主要代码实现在如下两个函数

__pci_read_base
pci_size

主要函数如下：


__pci_read_base
pci_read_config_dword(dev, pos, &l);
pci_write_config_dword(dev, pos, l | mask);
pci_read_config_dword(dev, pos, &sz);

pci_size
u64 size = mask & maxbase;
size = size & ~(size-1);

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