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 internal tamper

Internal tampers must be configured in OP-TEE device tree with the st,tamp-internal-tampers property. The following example configures two internal tampers:

&tamp {
	status = "okay";
	st,tamp_passive_nb_sample = <4>;
	st,tamp_passive_sample_clk_div = <16384>;
	st,tamp-internal-tampers =
		<INT_TAMPER_RTC_VOLTAGE_MONITORING TAMPER_CONFIRMED_MODE>,
		<INT_TAMPER_TEMPERATURE_MONITORING TAMPER_POTENTIAL_MODE>;
};

Configure an external tamper (passive)

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

&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 (gpioi 8) and raises a tamper event if the wrong data is read on the input pin (gpioc 1).

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

	tamp-active {
		/* tamper-gpios = <&TAMP_IN3> , <&TAMP_OUT3> */
		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";
	};
};