Linux 64位BAR编程

Question

PCI桥支持32/64首选项/无首选项：

pci_bus 0000:00: root bus resource [bus 00-ff]

pci_bus 0000:00: root bus resource [io  0x0000-0xffff] 

pci_bus 0000:00: root bus resource [mem 0x1000000000-0x10ffffffff] (bus address [0x00000000-0xffffffff])

pci_bus 0000:00: root bus resource [mem 0x1100000000-0x11ffffffff pref] (bus address [0x00000000-0xffffffff])

pci_bus 0000:00: root bus resource [mem 0x2000000000-0x2fffffffff] (bus address [0x00000000-0xfffffffff])

pci_bus 0000:00: root bus resource [mem 0x3000000000-0x3fffffffff pref] (bus  address [0x00000000-0xfffffffff])

扫描具有2条BAR的端点：

pci 0000:01:00.0: BAR 2: assigned [mem 0x2100000000-0x211fffffff 64bit pref]

pci 0000:01:00.0: BAR 0: assigned [mem 0x1000000000-0x100007ffff]

桥显示了窗口：

pci 0000:00:00.0: PCI bridge to [bus 01]

pci 0000:00:00.0:   bridge window [mem 0x1000000000-0x10000fffff]

pci 0000:00:00.0:   bridge window [mem 0x2100000000-0x211fffffff 64bit pref]

端点总结了BAR：

endpoint: BAR 0 addr = 0x1000000000, size = 524287

endpoint: BAR 1 addr = 0x2100000000, size = 536870911

BAR1的高32位将被编程为什么？我预期为0x21，但找到0x1。

这是因为pcibios_bus_to_resource / pcibios_resource_to_bus。它标识了3个窗口偏移：

window->res->start = 1000000000 window->offset = 1000000000 window->res->end = 10FFFFFFFF

window->res->start = 1100000000 window->offset = 1100000000 window->res->end = 11FFFFFFFF

window->res->start = 2000000000 window->offset = 2000000000 window->res->end = 2FFFFFFFFF

当显示上面的地址时，它会增加偏移量，而在端点中对BAR寄存器进行编程时，则将其减去。因此0x2100000000变为0x100000000。

使用64位地址和32位BAR可能会有意义，但是为什么使用64位BAR会正确呢？

Answer 1

据此（取自问题）：    pci_bus 0000:00: root bus resource [mem 0x1000000000-0x10ffffffff] (bus address [0x00000000-0xffffffff])    pci_bus 0000:00: root bus resource [mem 0x1100000000-0x11ffffffff pref] (bus address [0x00000000-0xffffffff])    pci_bus 0000:00: root bus resource [mem 0x2000000000-0x2fffffffff] (bus address [0x00000000-0xfffffffff])    pci_bus 0000:00: root bus resource [mem 0x3000000000-0x3fffffffff pref] (bus  address [0x00000000-0xfffffffff])存储器地址0x20'0000'0000对应于总线地址0。因此，如果要使用存储器地址0x21'0000'0000访问该设备中的BAR，则需要将其编程为0x1'0000'0000。同样，存储器地址0x10'0000'0000对应于总线地址0。因此，设备中的BAR被编程为0，可以使用存储器地址0x10'0000'0000进行访问。