platform: cznic: turris-omnia-mcu: Make TRNG code optional

Make the TRNG part of the driver optional, under a boolean config
option.

This makes the driver turris-omnia-mcu available for compilation even if
HW_RANDOM is disabled.

Fixes: ed46f1f7 ("platform: cznic: turris-omnia-mcu: fix Kconfig dependencies")
Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20240719085756.30598-3-kabel@kernel.orgSigned-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/platform/cznic/Kconfig

@@ -18,7 +18,6 @@ config TURRIS_OMNIA_MCU
 	depends on I2C
 	depends on OF
 	depends on GPIOLIB
-	depends on HW_RANDOM
 	depends on RTC_CLASS
 	select GPIOLIB_IRQCHIP
 	help
@@ -28,7 +27,6 @@ config TURRIS_OMNIA_MCU
 	  - board poweroff into true low power mode (with voltage regulators
 	    disabled) and the ability to configure wake up from this mode (via
 	    rtcwake)
-	  - true random number generator (if available on the MCU)
 	  - GPIO pins
 	    - to get front button press events (the front button can be
 	      configured either to generate press events to the CPU or to change
@@ -56,6 +54,14 @@ config TURRIS_OMNIA_MCU_WATCHDOG
 	  Say Y here to add support for watchdog provided by CZ.NIC's Turris
 	  Omnia MCU.
 
+config TURRIS_OMNIA_MCU_TRNG
+	bool "Turris Omnia MCU true random number generator"
+	default y
+	depends on HW_RANDOM
+	help
+	  Say Y here to add support for the true random number generator
+	  provided by CZ.NIC's Turris Omnia MCU.
+
 endif # TURRIS_OMNIA_MCU
 
 endif # CZNIC_PLATFORMS

drivers/platform/cznic/Makefile

@@ -4,5 +4,5 @@ obj-$(CONFIG_TURRIS_OMNIA_MCU)	+= turris-omnia-mcu.o
 turris-omnia-mcu-y		:= turris-omnia-mcu-base.o
 turris-omnia-mcu-y		+= turris-omnia-mcu-gpio.o
 turris-omnia-mcu-y		+= turris-omnia-mcu-sys-off-wakeup.o
-turris-omnia-mcu-y		+= turris-omnia-mcu-trng.o
+turris-omnia-mcu-$(CONFIG_TURRIS_OMNIA_MCU_TRNG)		+= turris-omnia-mcu-trng.o
 turris-omnia-mcu-$(CONFIG_TURRIS_OMNIA_MCU_WATCHDOG)		+= turris-omnia-mcu-watchdog.o

drivers/platform/cznic/turris-omnia-mcu.h

@@ -52,9 +52,11 @@ struct omnia_mcu {
 	struct watchdog_device wdt;
 #endif
 
+#ifdef CONFIG_TURRIS_OMNIA_MCU_TRNG
 	/* true random number generator */
 	struct hwrng trng;
 	struct completion trng_entropy_ready;
+#endif
 };
 
 int omnia_cmd_write_read(const struct i2c_client *client,
@@ -190,7 +192,15 @@ extern const struct attribute_group omnia_mcu_poweroff_group;
 
 int omnia_mcu_register_gpiochip(struct omnia_mcu *mcu);
 int omnia_mcu_register_sys_off_and_wakeup(struct omnia_mcu *mcu);
+
+#ifdef CONFIG_TURRIS_OMNIA_MCU_TRNG
 int omnia_mcu_register_trng(struct omnia_mcu *mcu);
+#else
+static inline int omnia_mcu_register_trng(struct omnia_mcu *mcu)
+{
+	return 0;
+}
+#endif
 
 #ifdef CONFIG_TURRIS_OMNIA_MCU_WATCHDOG
 int omnia_mcu_register_watchdog(struct omnia_mcu *mcu);