platform: cznic: turris-omnia-mcu: Add support for MCU provided TRNG

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>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/r/20240701113010.16447-7-kabel@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

diff --git a/drivers/platform/cznic/Kconfig b/drivers/platform/cznic/Kconfig
index e262930b3faf68a7f4fa75c57cb5afaba8ab5c40..6edac80d5fa377620760ec059ade35f9f2ace45b 100644 (file)
--- a/drivers/platform/cznic/Kconfig
+++ b/drivers/platform/cznic/Kconfig
@@ -18,6 +18,7 @@ config TURRIS_OMNIA_MCU
        depends on I2C
        select GPIOLIB
        select GPIOLIB_IRQCHIP
+       select HW_RANDOM
        select RTC_CLASS
        select WATCHDOG_CORE
        help
@@ -27,6 +28,7 @@ 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 687f7718c0a16f994016157c79a908516f10e41b..eae4c6b341fff776fd11759625a9eda4f28f42bd 100644 (file)
--- 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 2d8e5c9a8dd104011964b7127b76c2cdac6d1fb4..c68a7a84a9519a65005b23292bb32848acc50342 100644 (file)
--- a/drivers/platform/cznic/turris-omnia-mcu-base.c
+++ b/drivers/platform/cznic/turris-omnia-mcu-base.c
@@ -381,7 +381,11 @@ 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 7ffc9453eddbb007726eec1aa845070ed3d92fb5..91da56a704c7bc040c5c62ad03d2991eb1cf238c 100644 (file)
--- a/drivers/platform/cznic/turris-omnia-mcu-gpio.c
+++ b/drivers/platform/cznic/turris-omnia-mcu-gpio.c
@@ -195,7 +195,7 @@ static const struct omnia_gpio omnia_gpios[64] = {
 };
 
 /* 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(OMNIA_INT_CARD_DET)]                  = 4,
        [__bf_shf(OMNIA_INT_MSATA_IND)]                 = 5,
        [__bf_shf(OMNIA_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 (file)
index 0000000..ad953fb
--- /dev/null
+++ b/drivers/platform/cznic/turris-omnia-mcu-trng.c
@@ -0,0 +1,103 @@
+// 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/container_of.h>
+#include <linux/errno.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/string.h>
+#include <linux/types.h>
+
+#include <linux/turris-omnia-mcu-interface.h>
+#include "turris-omnia-mcu.h"
+
+#define OMNIA_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_entropy_ready);
+
+       return IRQ_HANDLED;
+}
+
+static int omnia_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
+{
+       struct omnia_mcu *mcu = container_of(rng, struct omnia_mcu, trng);
+       u8 reply[1 + OMNIA_CMD_TRNG_MAX_ENTROPY_LEN];
+       int err, bytes;
+
+       if (!wait && !completion_done(&mcu->trng_entropy_ready))
+               return 0;
+
+       do {
+               if (wait_for_completion_interruptible(&mcu->trng_entropy_ready))
+                       return -ERESTARTSYS;
+
+               err = omnia_cmd_read(mcu->client,
+                                    OMNIA_CMD_TRNG_COLLECT_ENTROPY,
+                                    reply, sizeof(reply));
+               if (err)
+                       return err;
+
+               bytes = min3(reply[0], max, OMNIA_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 & OMNIA_FEAT_TRNG))
+               return 0;
+
+       irq_idx = omnia_int_to_gpio_idx[__bf_shf(OMNIA_INT_TRNG)];
+       irq = gpiod_to_irq(gpio_device_get_desc(mcu->gc.gpiodev, irq_idx));
+       if (!irq)
+               return dev_err_probe(dev, -ENXIO, "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, OMNIA_CMD_TRNG_COLLECT_ENTROPY,
+                            &dummy, 1);
+       if (err)
+               return err;
+
+       init_completion(&mcu->trng_entropy_ready);
+
+       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;
+
+       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 dc59f415f611035e3e54117dbc5f12a0b8fb2563..2ca56ae13aa908c7fcf3782a336911f0716050cb 100644 (file)
--- 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/types.h>
@@ -47,6 +49,10 @@ struct omnia_mcu {
 
        /* MCU watchdog */
        struct watchdog_device wdt;
+
+       /* true random number generator */
+       struct hwrng trng;
+       struct completion trng_entropy_ready;
 };
 
 int omnia_cmd_write_read(const struct i2c_client *client,
@@ -176,11 +182,13 @@ static inline int omnia_cmd_read_u8(const struct i2c_client *client, u8 cmd,
        return omnia_cmd_read(client, cmd, reply, sizeof(*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 */