一，io命令简介
“io” 命令通常用于显示 Linux 系统中的 I/O 统计信息。它提供了有关磁盘读写操作的详细信息，包括每个块设备的读写次数、读写扇区数、读写延迟等。io命令可以直接操作某个寄存器，用于查看设置某个GPIO 引脚配置了什么iomux。
二，移植io命令驱动
RK 的 Android 平台，默认有包含 io 工具（源码位置：external\io）。
1. 在 Makefile 中添加mem
kernel/drivers/char/Makefile
增加
+obj-$(CONFIG_DEVMEM) += mem.o
2. 在 Kconfig 中添加DEVMEM
kernel/drivers/char/Kconfig
改文件已经包含下面信息
config DEVMEM
bool "/dev/mem virtual device support"
default y
help
Say Y here if you want to support the /dev/mem device.
The /dev/mem device is used to access areas of physical
memory.
When in doubt, say "Y".
3. 修改驱动文件
源码路径：
kernel/arch/arm/configs/rockchip_defconfig
kernel/drivers/char/mem.c
diff --git a/kernel/arch/arm/configs/rockchip_defconfig b/kernel/arch/arm/configs/rockchip_defconfig
index 0c930a731b..7116d1eafc 100644
--- a/kernel/arch/arm/configs/rockchip_defconfig
+++ b/kernel/arch/arm/configs/rockchip_defconfig
@@ -417,7 +417,7 @@ CONFIG_INPUT_RK805_PWRKEY=y
# CONFIG_SERIO is not set
# CONFIG_VT is not set
# CONFIG_LEGACY_PTYS is not set
-# CONFIG_DEVMEM is not set
+CONFIG_DEVMEM=y
CONFIG_SERIAL_8250=y
# CONFIG_SERIAL_8250_DEPRECATED_OPTIONS is not set
CONFIG_SERIAL_8250_CONSOLE=y
diff --git a/kernel/drivers/char/mem.c b/kernel/drivers/char/mem.c
index 54b86490d9..836b130049 100644
--- a/kernel/drivers/char/mem.c
+++ b/kernel/drivers/char/mem.c
@@ -881,9 +881,7 @@ static const struct memdev {
const struct file_operations *fops;
fmode_t fmode;
} devlist[] = {
-#ifdef CONFIG_DEVMEM
[1] = {
"mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET },
-#endif
#ifdef CONFIG_DEVKMEM
[2] = {
"kmem", 0, &kmem_fops, FMODE_UNSIGNED_OFFSET },
#endif
三，调试命令
1. 查看mem字符设备
io命令正是通过以下字符设备来实现寄存器的读写：
rk3568_r:/ # ls -l /dev/mem
crw------- 1 media media 1, 1 2017-08-04 09:00 /dev/mem
2. 命令说明
rk3568_r:/dev # io
io
Raw memory i/o utility - $Revision: 1.5 $
io -v -1|2|4 -r|w [-l <len>] [-f <file>] <addr> [<value>]
-v Verbose, asks for confirmation
-1|2|4 Sets memory access size in bytes (default byte)
-l <len> Length in bytes of area to access (defaults to
one access, or whole file length)
-r|w Read from or Write to memory (default read)
-f <file> File to write on memory read, or
to read on memory write
<addr> The memory address to access
<val> The value to write (implies -w)
Examples:
io 0x1000 Reads one byte from 0x1000
io 0x1000 0x12 Writes 0x12 to location 0x1000
io -2 -l 8 0x1000 Reads 8 words from 0x1000
io -r -f dmp -l 100 200 Reads 100 bytes from addr 200 to file
io -w -f img 0x10000 Writes the whole of file to memory
Note access size (-1|2|4) does not apply to file based accesses.