如何在64位Linux内核环境中读取32位PCI内存 [英] How to read 32-bit PCI bar memory in 64-bit linux kernel environment

问题描述

我想在我的PCIe设备上进行I/O.我正在运行带有Linux内核4.4.0的Ubuntu 16.0.4 LTS

I want to do I/O on my PCIe device.I am running Ubuntu 16.0.4 LTS with linux kernel 4.4.0

lspci -v 命令的输出为:

06:00.0 Unclassified device [00ff]: Device 1aa1:2000 (rev 01)
    Subsystem: Device 1aa1:2000
    Physical Slot: 1-4
    Flags: bus master, fast devsel, latency 0, IRQ 16
    Memory at f1008000 (32-bit, non-prefetchable) [size=8K]
    Memory at ee000000 (32-bit, non-prefetchable) [size=32M]
    Memory at f100a000 (32-bit, non-prefetchable) [size=4K]
    Memory at f0000000 (32-bit, non-prefetchable) [size=16M]
    Memory at f1000000 (32-bit, non-prefetchable) [size=32K]
    Capabilities: <access denied>
    Kernel driver in use: my_pci
    Kernel modules: my_pci

很显然，PCI地址是32位的.

Clearly, PCI addresses are 32-bit.

我想知道如何使用ioread32/iowrite32函数读取/写入BAR地址.我机器上的 unsigned char __iomem * mem 类型将是64位，如果我使用以下说法:

I want to know how to use ioread32/iowrite32 functions to read/write into the BAR addresses. unsigned char __iomem *mem types on my machine would be 64-bit and if I use the following say :

ioread32(mem + some_offset);

表达式 mem + some_offset 将是64位，并导致崩溃.

The expression mem + some_offset would be 64-bit and result into crash.

我将如何执行I/O?

推荐答案

正在使用的PCI设备使用32位寻址模式.当您的PC枚举BAR并将物理地址写入BAR时.它写入一个掩码值，仅是64位的低32位(在主机地址空间中)在驱动程序上打印OS/BIOS分配给此BAR的物理地址并进行比较.

The PCI devices you're working with works using 32bit addressing mode. when your PC enumerates the BARs and writes the physical address onto the BAR. it writes a masked values, only the lower 32 bit of the 64 bit (in host address space) Print the physical address the OS/BIOS has assigned to this BAR on the driver and compare it.

此外，这是一个物理地址，因此您无论如何都不能对其进行 iowrite .

besides, this is a physical address, so you can't iowrite to it anyway.

所以我不太了解你的目标.

So I don't really understand your goal.

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