This project is using linux kernel legacy gpio to control reset and boot mode of any mcu.Tested on linux kernel version 3.10.49 For newer version, checkout branch 3.18

In order to run this module, device tree must have node name gpio-boot-reset The driver will parse flowing propreties of gpio-boot-reset's child node

• reset: propreties that point to the that connect to reset pin of mcu (mandatory)
• boot: propreties that point to gpio that connect to boot pin of mcu (mandatory)
• reset-time: time of each reset pluse, default: 25 (unit: us) (optional)
• boot-time: time to hold boot pin after reset complete, default: 10 (unit: us) (optional)
• reset-active-low: boolean, determine reset gpio pin is active low (optional)
• boot-active-low: boolean, determine boot gpio pin is active low (optional)

Example:

gpio-boot-reset{
    compatible = "gpio-boot-reset";
    status = "okay";

    pinctrl-0 = <&reset_pin_off>;
    stm32f042c4{
            reset = <&msm_gpio 95 0>;
            boot = <&msm_gpio 17 0>;
            reset-time = <20>;
            boot-time = <10>;
    };

    nfc {
            reset = <&msm_gpio 16 0>;
            boot = <&msm_gpio 93 0>;
            reset-time = <20>;
            boot-time = <3000>;
    };
};

example's external pinctrl-0

reset_pin { 
    qcom,pins = <&gp 95>, <&gp 17>, <&gp 16>, <&gp 93> ;

    qcom,num-grp-pins = <4>;
    label = "reset-gpio-pins";
    reset_pin_off: stm32f042c4_gpio_off {
        drive-strength = <2>;
        bias-disable; /* no pullup */
        output-low;
    };
};

This module only support 1 reset and boot partern only:

• Reset: reset high -> wait for reset-time -> reset low
• Boot: boot high -> reset high -> wair for reset-time > reset low -> wait for boot-time -> boot low

Provide your target kernel using KERNEL_SRC (default is host kernel directory /lib/modules/$(shell uname -r )/build) variable using following code

make KERNEL_SRC=/PATH/TO/YOUR/KERNEL/SOURCE

To clean unnecessary file

make clean

After install module into kernel, there will be 1 file attribute for each child node /sys/class/gpio_boot_reset/*/mode To reset MCU use

echo -n "normal" > /sys/class/gpio_boot_reset/{child_node_name}/mode

To enter bootloader mode

echo -n "prog" > /sys/class/gpio_boot_reset/{child_node_name}/mode

With example device tree above, we will have 2 folder, which coresponse to 2 child node in device tree: /sys/class/gpio_boot_reset/stm32f042c4/mode and /sys/class/gpio_boot_reset/nfc/mode

This project is licensed under the GPLv2 License - see the LICENSE file for details