[PATCH v8 6/9] platform: cznic: turris-omnia-mcu: Add support for MCU provided TRNG

["Marek Behún" <kabel@kernel.org>]

Add support for true random number generator provided by the MCU.
New Omnia boards come without the Atmel SHA204-A chip. Instead the
crypto functionality is provided by new microcontroller, which has
a TRNG peripheral.

Signed-off-by: Marek Behún <kabel@kernel.org>
---
 drivers/platform/cznic/Kconfig                |   2 +
 drivers/platform/cznic/Makefile               |   1 +
 .../platform/cznic/turris-omnia-mcu-base.c    |   6 +-
 .../platform/cznic/turris-omnia-mcu-gpio.c    |   2 +-
 .../platform/cznic/turris-omnia-mcu-trng.c    | 101 ++++++++++++++++++
 drivers/platform/cznic/turris-omnia-mcu.h     |   8 ++
 6 files changed, 118 insertions(+), 2 deletions(-)
 create mode 100644 drivers/platform/cznic/turris-omnia-mcu-trng.c

diff --git a/drivers/platform/cznic/Kconfig b/drivers/platform/cznic/Kconfig
index e2649cdecc38..750d5f47dba8 100644
--- a/drivers/platform/cznic/Kconfig
+++ b/drivers/platform/cznic/Kconfig
@@ -19,6 +19,7 @@ config TURRIS_OMNIA_MCU
 	depends on I2C
 	select GPIOLIB
 	select GPIOLIB_IRQCHIP
+	select HW_RANDOM
 	select RTC_CLASS
 	select WATCHDOG_CORE
 	help
@@ -28,6 +29,7 @@ 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)
 	  - MCU watchdog
 	  - GPIO pins
 	    - to get front button press events (the front button can be
diff --git a/drivers/platform/cznic/Makefile b/drivers/platform/cznic/Makefile
index 687f7718c0a1..eae4c6b341ff 100644
--- a/drivers/platform/cznic/Makefile
+++ b/drivers/platform/cznic/Makefile
@@ -4,4 +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-y		+= turris-omnia-mcu-watchdog.o
diff --git a/drivers/platform/cznic/turris-omnia-mcu-base.c b/drivers/platform/cznic/turris-omnia-mcu-base.c
index 5f88119d825c..7fe4a3df93a6 100644
--- a/drivers/platform/cznic/turris-omnia-mcu-base.c
+++ b/drivers/platform/cznic/turris-omnia-mcu-base.c
@@ -369,7 +369,11 @@ static int omnia_mcu_probe(struct i2c_client *client)
 	if (err)
 		return err;
 
-	return omnia_mcu_register_gpiochip(mcu);
+	err = omnia_mcu_register_gpiochip(mcu);
+	if (err)
+		return err;
+
+	return omnia_mcu_register_trng(mcu);
 }
 
 static const struct of_device_id of_omnia_mcu_match[] = {
diff --git a/drivers/platform/cznic/turris-omnia-mcu-gpio.c b/drivers/platform/cznic/turris-omnia-mcu-gpio.c
index bcc12bd1453c..af20f8076857 100644
--- a/drivers/platform/cznic/turris-omnia-mcu-gpio.c
+++ b/drivers/platform/cznic/turris-omnia-mcu-gpio.c
@@ -163,7 +163,7 @@ static const struct omnia_gpio {
 };
 
 /* mapping from interrupts to indexes of GPIOs in the omnia_gpios array */
-static const u8 omnia_int_to_gpio_idx[32] = {
+const u8 omnia_int_to_gpio_idx[32] = {
 	[__bf_shf(INT_CARD_DET)]		= 4,
 	[__bf_shf(INT_MSATA_IND)]		= 5,
 	[__bf_shf(INT_USB30_OVC)]		= 6,
diff --git a/drivers/platform/cznic/turris-omnia-mcu-trng.c b/drivers/platform/cznic/turris-omnia-mcu-trng.c
new file mode 100644
index 000000000000..b85550dea4ad
--- /dev/null
+++ b/drivers/platform/cznic/turris-omnia-mcu-trng.c
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * CZ.NIC's Turris Omnia MCU TRNG driver
+ *
+ * 2024 by Marek Behún <kabel@kernel.org>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/completion.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/hw_random.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/minmax.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/turris-omnia-mcu-interface.h>
+#include <linux/types.h>
+
+#include "turris-omnia-mcu.h"
+
+#define CMD_TRNG_MAX_ENTROPY_LEN	64
+
+static irqreturn_t omnia_trng_irq_handler(int irq, void *dev_id)
+{
+	struct omnia_mcu *mcu = dev_id;
+
+	complete(&mcu->trng_completion);
+
+	return IRQ_HANDLED;
+}
+
+static int omnia_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
+{
+	struct omnia_mcu *mcu = (struct omnia_mcu *)rng->priv;
+	u8 reply[1 + CMD_TRNG_MAX_ENTROPY_LEN];
+	int err, bytes;
+
+	if (!wait && !completion_done(&mcu->trng_completion))
+		return 0;
+
+	do {
+		if (wait_for_completion_interruptible(&mcu->trng_completion))
+			return -EINTR;
+
+		err = omnia_cmd_read(mcu->client, CMD_TRNG_COLLECT_ENTROPY,
+				     reply, sizeof(reply));
+		if (err)
+			return err;
+
+		bytes = min3(reply[0], max, CMD_TRNG_MAX_ENTROPY_LEN);
+	} while (wait && !bytes);
+
+	memcpy(data, &reply[1], bytes);
+
+	return bytes;
+}
+
+int omnia_mcu_register_trng(struct omnia_mcu *mcu)
+{
+	struct device *dev = &mcu->client->dev;
+	u8 irq_idx, dummy;
+	int irq, err;
+
+	if (!(mcu->features & FEAT_TRNG))
+		return 0;
+
+	irq_idx = omnia_int_to_gpio_idx[__bf_shf(INT_TRNG)];
+	irq = gpiod_to_irq(gpiochip_get_desc(&mcu->gc, irq_idx));
+	if (irq < 0)
+		return dev_err_probe(dev, irq, "Cannot get TRNG IRQ\n");
+
+	/*
+	 * If someone else cleared the TRNG interrupt but did not read the
+	 * entropy, a new interrupt won't be generated, and entropy collection
+	 * will be stuck. Ensure an interrupt will be generated by executing
+	 * the collect entropy command (and discarding the result).
+	 */
+	err = omnia_cmd_read(mcu->client, CMD_TRNG_COLLECT_ENTROPY, &dummy, 1);
+	if (err)
+		return err;
+
+	init_completion(&mcu->trng_completion);
+
+	err = devm_request_threaded_irq(dev, irq, NULL, omnia_trng_irq_handler,
+					IRQF_ONESHOT, "turris-omnia-mcu-trng",
+					mcu);
+	if (err)
+		return dev_err_probe(dev, err, "Cannot request TRNG IRQ\n");
+
+	mcu->trng.name = "turris-omnia-mcu-trng";
+	mcu->trng.read = omnia_trng_read;
+	mcu->trng.priv = (unsigned long)mcu;
+
+	err = devm_hwrng_register(dev, &mcu->trng);
+	if (err)
+		return dev_err_probe(dev, err, "Cannot register TRNG\n");
+
+	return 0;
+}
diff --git a/drivers/platform/cznic/turris-omnia-mcu.h b/drivers/platform/cznic/turris-omnia-mcu.h
index 1838cb3d636e..e0cf10f8c32e 100644
--- a/drivers/platform/cznic/turris-omnia-mcu.h
+++ b/drivers/platform/cznic/turris-omnia-mcu.h
@@ -9,7 +9,9 @@
 #define __TURRIS_OMNIA_MCU_H
 
 #include <linux/bitops.h>
+#include <linux/completion.h>
 #include <linux/gpio/driver.h>
+#include <linux/hw_random.h>
 #include <linux/if_ether.h>
 #include <linux/mutex.h>
 #include <linux/rtc.h>
@@ -45,6 +47,10 @@ struct omnia_mcu {
 
 	/* MCU watchdog */
 	struct watchdog_device wdt;
+
+	/* true random number generator */
+	struct hwrng trng;
+	struct completion trng_completion;
 };
 
 int omnia_cmd_write_read(const struct i2c_client *client,
@@ -147,11 +153,13 @@ static inline int omnia_cmd_read_u8(const struct i2c_client *client, u8 cmd)
 	return err ?: reply;
 }
 
+extern const u8 omnia_int_to_gpio_idx[32];
 extern const struct attribute_group omnia_mcu_gpio_group;
 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);
+int omnia_mcu_register_trng(struct omnia_mcu *mcu);
 int omnia_mcu_register_watchdog(struct omnia_mcu *mcu);
 
 #endif /* __TURRIS_OMNIA_MCU_H */
-- 
2.43.2