TQIMX6UL 内核版本4.1.15
以下使用扩展接口的PWM2_OUT引脚为例介绍修改一个被占用的管脚，将其修改为普通gpio
1.在引脚定义arch/arm/boot/dts/imx6ul-pinfunc.h文件中搜索 PWM2_OUT,搜索的结果如下所示:

#define MX6UL_PAD_GPIO1_IO09__PWM2_OUT                            0x0080 0x030C 0x0000 0x0 0x0
#define MX6UL_PAD_GPIO1_IO09__WDOG1_WDOG_ANY                      0x0080 0x030C 0x0000 0x1 0x0
#define MX6UL_PAD_GPIO1_IO09__SPDIF_IN                            0x0080 0x030C 0x0618 0x2 0x0
#define MX6UL_PAD_GPIO1_IO09__CSI_HSYNC                           0x0080 0x030C 0x0524 0x3 0x1
#define MX6UL_PAD_GPIO1_IO09__USDHC2_RESET_B                      0x0080 0x030C 0x0000 0x4 0x0
#define MX6UL_PAD_GPIO1_IO09__GPIO1_IO09                          0x0080 0x030C 0x0000 0x5 0x0
#define MX6UL_PAD_GPIO1_IO09__USDHC1_RESET_B                      0x0080 0x030C 0x0000 0x6 0x0
#define MX6UL_PAD_GPIO1_IO09__UART5_DCE_CTS                       0x0080 0x030C 0x0000 0x8 0x0
#define MX6UL_PAD_GPIO1_IO09__UART5_DTE_RTS  

从搜索可以看出，PWM2_OUT对应的GPIO是GPIO1_IO09管脚

2.打开 arch/arm/boot/dts/tq-imx6ul.dts，搜索 PWM2_OUT
pinctrl_pwm2: pwm2grp {
                        fsl,pins = <
                                MX6UL_PAD_GPIO1_IO09__PWM2_OUT  0x110b0
                        >;
                };

可知 PWM2_OUT被用于串口 PWM2.
搜索pinctrl_pwm2将status改为disabled关闭该pwm2引脚功能
&pwm4 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_pwm4>;
        clocks = <&clks IMX6UL_CLK_PWM4>,
                        <&clks IMX6UL_CLK_PWM4>;
        clock-names = "ipg", "per";
        status = "disabled";
};
再搜索gpio1 9相关，将gpio = <&gpio1 9 GPIO_ACTIVE_HIGH>;屏蔽
reg_sd1_vmmc: regulator@1 {
                        compatible = "regulator-fixed";
                        regulator-name = "VSD_3V3";
                        regulator-min-microvolt = <3300000>;
                        regulator-max-microvolt = <3300000>;
                        //gpio = <&gpio1 9 GPIO_ACTIVE_HIGH>;
                        enable-active-high;
                };


3.将 PWM2_OUT配置成 gpio:
搜索 imx6ul-evk，在组里面添加步骤 1搜索到的 gpio，MX6UL_PAD_GPIO1_IO09__GPIO1_IO09 
imx6ul-evk {
                    pinctrl_gpmi_nand_1: gpmi-nand-1 {
                        fsl,pins = <
			    ...
                            MX6UL_PAD_NAND_CE1_B__RAWNAND_CE1_B     0xb0b1
                            MX6UL_PAD_NAND_RE_B__RAWNAND_RE_B       0xb0b1
                            MX6UL_PAD_NAND_WE_B__RAWNAND_WE_B       0xb0b1
                            MX6UL_PAD_NAND_DATA00__RAWNAND_DATA00   0xb0b1
                            MX6UL_PAD_NAND_DATA01__RAWNAND_DATA01   0xb0b1
                            MX6UL_PAD_NAND_DATA02__RAWNAND_DATA02   0xb0b1
                            MX6UL_PAD_NAND_DATA03__RAWNAND_DATA03   0xb0b1
                            MX6UL_PAD_NAND_DATA04__RAWNAND_DATA04   0xb0b1
                            MX6UL_PAD_NAND_DATA05__RAWNAND_DATA05   0xb0b1
                            MX6UL_PAD_NAND_DATA06__RAWNAND_DATA06   0xb0b1
                            MX6UL_PAD_NAND_DATA07__RAWNAND_DATA07   0xb0b1

			    MX6UL_PAD_GPIO1_IO09__GPIO1_IO09 	    0xb0b1
                        >;
                    };

6.检查哪里还有配置GPIO1_IO09或者PWM2_OUT相关定义，没有则可重新编译，将修改后的设备树烧录至板子。

7.应用层测试：

编号计算：引脚编号 = 控制引脚的寄存器基数 + 控制引脚寄存器位数
    举例:
    GPIO为GPIO1_09，引脚编号为32*(1-0)+9=9
    GPIO为GPIO3_21，引脚编号为32*(3-1)+21=85

echo 9 > /sys/class/gpio/export			//映射引脚
echo "out" > /sys/class/gpio/gpio9/direction	//设置定义输入输入方向，out为输出，in为输入
echo 1 > /sys/class/gpio/gpio9/value		//设置高电平
echo 0 > /sys/class/gpio/gpio9/value		//设置低电平

使用万用表测量电压，如果设置的电平和量出电平一致则该GPIO修改成功为普通可控GPIO，如果提示busy则改脚未修改成功，需重新检查设备树。