[PATCH v5 07/11] platform: cznic: turris-omnia-mcu: Add support for MCU provided TRNG

Marek Behún
2024-03-23T16:44:23Z

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 | 89 +++++++++++++++++++
drivers/platform/cznic/turris-omnia-mcu.h | 8 ++
6 files changed, 106 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 a43997a12d74..8fd4c6cbcb1b 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-objs := turris-omnia-mcu-base.o
turris-omnia-mcu-objs += turris-omnia-mcu-gpio.o
turris-omnia-mcu-objs += turris-omnia-mcu-sys-off-wakeup.o
+turris-omnia-mcu-objs += turris-omnia-mcu-trng.o
turris-omnia-mcu-objs += 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 5a45834003cd..30771004a627 100644
--- a/drivers/platform/cznic/turris-omnia-mcu-base.c
+++ b/drivers/platform/cznic/turris-omnia-mcu-base.c
@@ -335,7 +335,11 @@ 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 7f885be23a47..90b2caa679ea 100644
--- a/drivers/platform/cznic/turris-omnia-mcu-gpio.c
+++ b/drivers/platform/cznic/turris-omnia-mcu-gpio.c
@@ -161,7 +161,7 @@ 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..b08111b5c337
--- /dev/null
+++ b/drivers/platform/cznic/turris-omnia-mcu-trng.c
@@ -0,0 +1,89 @@
+// 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/devm-helpers.h>
+#include <linux/irqdomain.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;
+ int irq, err;
+ u8 irq_idx;
+
+ if (!(mcu->features & FEAT_TRNG))
+ return 0;
+
+ irq_idx = omnia_int_to_gpio_idx[__bf_shf(INT_TRNG)];
+ irq = devm_irq_create_mapping(dev, mcu->gc.irq.domain, irq_idx);
+ if (irq <= 0)
+ return dev_err_probe(dev, irq ?: -ENXIO,
+ "Cannot map TRNG IRQ\n");
+
+ 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 3e2c96079e64..f5b8f7ed3e6e 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/i2c.h>
#include <linux/if_ether.h>
#include <linux/mutex.h>
@@ -46,6 +48,10 @@ struct omnia_mcu {

/* MCU watchdog */
struct watchdog_device wdt;
+
+ /* true random number generator */
+ struct hwrng trng;
+ struct completion trng_completion;
};

static inline int omnia_cmd_write(const struct i2c_client *client, void *cmd,
@@ -166,11 +172,13 @@ 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