This topic only covers the configuration of external tamper pins. Refer to the STM32MP15 Hardware Reference Manual for information on internal tampers.

Device tree configuration

The TAMP controller is a secure peripheral and, as such, it can only be configured in OP-TEE device tree. The device tree binding is documented at https://github.com/digi-embedded/optee_os/blob/4.0.0/stm/maint/documentation/devicetree/bindings/hwmon/st%2Cstm32-tamp.yaml.

Configure an external tamper (passive)

The following example configures GPIOI_IO8 as a passive tamper. Passive tamper detects level/edge changes on the pin. The following example configures a rising-edge detection:

STM32MP15 device tree
&tamp {
	status = "okay";
	st,tamp_passive_nb_sample = <4>;
	st,tamp_passive_sample_clk_div = <16384>;

	tamp-passive {
		tamper-gpios = <&gpioi 8 GPIO_STM32_NSEC>;
		st,tamp-mode = <TAMPER_CONFIRMED_MODE>;
		st,tamp-id = <2>;
		status = "okay";
	};
};

Configure an external tamper (active)

The following example configures two pads, (GPIOC_IO1 and GPIOI_IO8) as active tamper. The two pads must be externally connected to each other. Active tamper sends periodic random values on the output pin and raises a tamper event if the wrong data is read on the input pin.

You can configure the number of mismatches detected before the system raises a tamper event.
STM32MP15 device tree
&tamp {
	status = "okay";

	tamp-active {
		tamper-gpios = <&gpioc 1 GPIO_STM32_NSEC>, <&gpioi 8 GPIO_STM32_NSEC>;
		st,tamp-mode = <TAMPER_CONFIRMED_MODE>;
		st,tamp-id = <3>, <3>;
		status = "okay";
	};
};