zephyr: Add support for RNG devices

This patch provides implementation of trng_rand_bytes() using Zephyr's
entropy API. Zephyr driver is responsible for hardware initialization,
enabling and disabling, so trng_init() and trng_exit() are no-op.

Add hostcmd and console command which can be used to test random number
generator. Both commands have unit tests implemented.

BUG=b:277029648
BRANCH=none
TEST=zmake build bloonchipper
TEST=Enable CONFIG_PLATFORM_EC_CONSOLE_CMD_RAND and compile firmware.
     Use 'rand' command to check if random values are generated.
TEST=./twister -v -i -T zephyr/test/drivers/ --test drivers.random

Change-Id: I3fa2c6a1aaf84dc23a8fbb06e557d9e07f5d1d32
Signed-off-by: Patryk Duda <pdk@semihalf.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/4381919
Tested-by: Patryk Duda <patrykd@google.com>
Commit-Queue: Patryk Duda <patrykd@google.com>
Reviewed-by: Keith Short <keithshort@chromium.org>

3 files changed, 75 insertions, 0 deletions

diff --git a/zephyr/shim/include/config_chip.h b/zephyr/shim/include/config_chip.h
index 2659ac66ce..3bb72ff8cf 100644
--- a/zephyr/shim/include/config_chip.h
+++ b/zephyr/shim/include/config_chip.h
@@ -2368,6 +2368,11 @@ BUILD_ASSERT((DT_NUM_INST_STATUS_OKAY(maxim_max695x)) == 1,
 #define CONFIG_PANIC_CONSOLE_OUTPUT
 #endif
 
+#undef CONFIG_RNG
+#ifdef CONFIG_PLATFORM_EC_RANDOM
+#define CONFIG_RNG
+#endif
+
 #undef CONFIG_CMD_CRASH
 #ifdef CONFIG_PLATFORM_EC_CONSOLE_CMD_CRASH
 #define CONFIG_CMD_CRASH
diff --git a/zephyr/shim/src/CMakeLists.txt b/zephyr/shim/src/CMakeLists.txt
index 17932540e4..a2d87f5571 100644
--- a/zephyr/shim/src/CMakeLists.txt
+++ b/zephyr/shim/src/CMakeLists.txt
@@ -55,6 +55,7 @@ zephyr_library_sources_ifdef(CONFIG_CROS_EC_POWER_SIGNAL_LIST
 							    power.c)
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_PWM_HC      pwm_hc.c)
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_LED_PWM     pwm_led.c)
+zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_RANDOM      random.c)
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_RTC         rtc.c)
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_SWITCHCAP_GPIO
 							    switchcap_gpio.c)
diff --git a/zephyr/shim/src/random.c b/zephyr/shim/src/random.c
new file mode 100644
index 0000000000..a18d83066e
--- /dev/null
+++ b/zephyr/shim/src/random.c
@@ -0,0 +1,69 @@
+/* Copyright 2023 The ChromiumOS Authors
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "console.h"
+#include "host_command.h"
+#include "printf.h"
+#include "system.h"
+
+#include <zephyr/drivers/entropy.h>
+#include <zephyr/kernel.h>
+
+#define rng DEVICE_DT_GET(DT_CHOSEN(zephyr_entropy))
+
+void trng_rand_bytes(void *buffer, size_t len)
+{
+	/*
+	 * In EC, we use size_t to represent buffer size, but Zephyr uses
+	 * uint16_t. Crash the system if user requested more than UINT16_MAX
+	 * bytes.
+	 */
+	if (!device_is_ready(rng) || len > UINT16_MAX)
+		k_oops();
+
+	if (entropy_get_entropy(rng, (uint8_t *)buffer, (uint16_t)len))
+		k_oops();
+}
+
+#if defined(CONFIG_PLATFORM_EC_CONSOLE_CMD_RAND)
+static int command_rand(const struct shell *shell, int argc, const char **argv)
+{
+	uint8_t data[32];
+	char str_buf[hex_str_buf_size(sizeof(data))];
+
+	trng_rand_bytes(data, sizeof(data));
+
+	snprintf_hex_buffer(str_buf, sizeof(str_buf),
+			    HEX_BUF(data, sizeof(data)));
+	shell_fprintf(shell, SHELL_NORMAL, "rand %s\n", str_buf);
+
+	return EC_SUCCESS;
+}
+SHELL_CMD_REGISTER(rand, NULL, "Output random bytes to console.", command_rand);
+#endif
+
+#if defined(CONFIG_PLATFORM_EC_HOSTCMD_RAND)
+static enum ec_status host_command_rand(struct host_cmd_handler_args *args)
+{
+	const struct ec_params_rand_num *p = args->params;
+	struct ec_response_rand_num *r = args->response;
+	uint16_t num_rand_bytes = p->num_rand_bytes;
+
+	if (system_is_locked())
+		return EC_RES_ACCESS_DENIED;
+
+	if (num_rand_bytes > args->response_max)
+		return EC_RES_OVERFLOW;
+
+	trng_rand_bytes(r->rand, num_rand_bytes);
+
+	args->response_size = num_rand_bytes;
+
+	return EC_RES_SUCCESS;
+}
+
+DECLARE_HOST_COMMAND(EC_CMD_RAND_NUM, host_command_rand,
+		     EC_VER_MASK(EC_VER_RAND_NUM));
+#endif