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entropy: rpi_pico: implement entropy driver for RP2350 #83346

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entropy: rpi_pico: implement entropy driver for RP2350 #83346

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4 changes: 4 additions & 0 deletions boards/raspberrypi/rpi_pico2/rpi_pico2.dtsi
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Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,10 @@ gpio0_lo: &gpio0 {
status = "okay";
};

&rng {
status = "okay";
};

zephyr_udc0: &usbd {
status = "okay";
};
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1 change: 1 addition & 0 deletions boards/raspberrypi/rpi_pico2/rpi_pico2_rp2350a_m33.yaml
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Expand Up @@ -12,6 +12,7 @@ supported:
- clock
- counter
- dma
- entropy
- gpio
- hwinfo
- i2c
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1 change: 1 addition & 0 deletions drivers/entropy/CMakeLists.txt
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Expand Up @@ -34,6 +34,7 @@ zephyr_library_sources_ifdef(CONFIG_ENTROPY_NXP_ELE_TRNG entropy_nxp_ele.
zephyr_library_sources_ifdef(CONFIG_ENTROPY_NXP_ELS_TRNG entropy_nxp_els_trng.c)
zephyr_library_sources_ifdef(CONFIG_ENTROPY_PSA_CRYPTO_RNG entropy_psa_crypto.c)
zephyr_library_sources_ifdef(CONFIG_ENTROPY_RENESAS_RA entropy_renesas_ra.c)
zephyr_library_sources_ifdef(CONFIG_ENTROPY_RPI_PICO_RNG entropy_rpi_pico.c)
zephyr_library_sources_ifdef(CONFIG_ENTROPY_RV32M1_TRNG entropy_rv32m1_trng.c)
zephyr_library_sources_ifdef(CONFIG_ENTROPY_SAM_RNG entropy_sam.c)
zephyr_library_sources_ifdef(CONFIG_ENTROPY_SILABS_SIWX91X entropy_silabs_siwx91x.c)
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1 change: 1 addition & 0 deletions drivers/entropy/Kconfig
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Expand Up @@ -40,6 +40,7 @@ source "drivers/entropy/Kconfig.nrf_cracen"
source "drivers/entropy/Kconfig.nxp"
source "drivers/entropy/Kconfig.psa_crypto"
source "drivers/entropy/Kconfig.renesas_ra"
source "drivers/entropy/Kconfig.rpi_pico"
source "drivers/entropy/Kconfig.rv32m1"
source "drivers/entropy/Kconfig.sam"
source "drivers/entropy/Kconfig.siwx91x"
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14 changes: 14 additions & 0 deletions drivers/entropy/Kconfig.rpi_pico
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@@ -0,0 +1,14 @@
# Raspberry Pi Pico entropy generator driver configuration

# Copyright (c) 2024 Xudong Zheng
# SPDX-License-Identifier: Apache-2.0

config ENTROPY_RPI_PICO_RNG
bool "Raspberry Pi Pico entropy number generator driver"
default y
depends on DT_HAS_RASPBERRYPI_PICO_RNG_ENABLED
depends on SOC_SERIES_RP2350
select ENTROPY_HAS_DRIVER
select PICOSDK_USE_CLAIM
select PICOSDK_USE_RAND
select PICOSDK_USE_TIMER
43 changes: 43 additions & 0 deletions drivers/entropy/entropy_rpi_pico.c
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@@ -0,0 +1,43 @@
/*
* Copyright (c) 2024 Xudong Zheng
*
* SPDX-License-Identifier: Apache-2.0
*/

#include <string.h>
#include <pico/rand.h>
#include <zephyr/drivers/entropy.h>
#include <zephyr/spinlock.h>

#define DT_DRV_COMPAT raspberrypi_pico_rng

static struct k_spinlock entropy_lock;

static int entropy_rpi_pico_get_entropy(const struct device *dev, uint8_t *buf, uint16_t len)
{
__ASSERT_NO_MSG(buf != NULL);
uint8_t *buf_bytes = buf;

while (len > 0) {
uint64_t value;
size_t to_copy = MIN(sizeof(value), len);

K_SPINLOCK(&entropy_lock) {
value = get_rand_64();
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@dsseng dsseng Aug 16, 2025

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Is it idiomatic for an entropy source to actually provide more entropy than it has? It only has a boot-time true random value, while this function is fueled by xoroshiro128 algorithm: https://github.com/raspberrypi/pico-sdk/blob/a1438dff1d38bd9c65dbd693f0e5db4b9ae91779/src/host/pico_rand/rand.c

This is a question to subsys maintainers

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@xudongzheng xudongzheng Aug 18, 2025

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Looking at https://github.com/raspberrypi/pico-sdk/blob/a1438dff1d38bd9c65dbd693f0e5db4b9ae91779/src/rp2_common/pico_rand/rand.c#L350-L354, each get_rand_64() invocation calls capture_additional_trng_samples() for additional entropy.

The end result is fed into xoroshiro128 as you mentioned.

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Hm, not sure if that matches subsystem expectations, but that sounds good. Please keep this thread open

}
memcpy(buf_bytes, &value, to_copy);
buf_bytes += to_copy;
len -= to_copy;
}

return 0;
}

static DEVICE_API(entropy, entropy_rpi_pico_api_funcs) = {
.get_entropy = entropy_rpi_pico_get_entropy
};

DEVICE_DT_INST_DEFINE(0,
NULL, NULL, NULL, NULL,
PRE_KERNEL_1, CONFIG_ENTROPY_INIT_PRIORITY,
&entropy_rpi_pico_api_funcs);
8 changes: 8 additions & 0 deletions dts/bindings/rng/raspberrypi,pico-rng.yaml
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@@ -0,0 +1,8 @@
# Copyright (c) 2024 Xudong Zheng
# SPDX-License-Identifier: Apache-2.0

description: Raspberry Pi Pico RNG/Entropy

compatible: "raspberrypi,pico-rng"

include: base.yaml
10 changes: 10 additions & 0 deletions dts/vendor/raspberrypi/rpi_pico/rp2350.dtsi
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Expand Up @@ -21,6 +21,10 @@
die-temp0 = &die_temp;
};

chosen {
zephyr,entropy = &rng;
};

cpus {
#address-cells = <1>;
#size-cells = <0>;
Expand Down Expand Up @@ -453,6 +457,12 @@
interrupt-names = "irq0", "irq1";
status = "disabled";
};

rng: rng@400f0000 {
compatible = "raspberrypi,pico-rng";
reg = <0x400f0000 DT_SIZE_K(4)>;
status = "disabled";
};
};

pinctrl: pin-controller {
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12 changes: 12 additions & 0 deletions modules/hal_rpi_pico/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -157,6 +157,18 @@ if(CONFIG_HAS_RPI_PICO)
zephyr_include_directories_ifdef(CONFIG_PICOSDK_USE_CLAIM
${common_dir}/hardware_claim/include)

zephyr_library_sources_ifdef(CONFIG_PICOSDK_USE_RAND
${rp2_common_dir}/pico_rand/rand.c
)
zephyr_include_directories_ifdef(CONFIG_PICOSDK_USE_RAND
${common_dir}/pico_sync/include
${common_dir}/pico_time/include
${rp2_common_dir}/pico_rand/include
${rp2_common_dir}/pico_time_adapter/include
${rp2_common_dir}/pico_unique_id/include
)
zephyr_linker_sources_ifdef(CONFIG_PICOSDK_USE_RAND DATA_SECTIONS uninit_data.ld)

zephyr_include_directories_ifdef(CONFIG_RISCV
${common_dir}/pico_sync/include
${common_dir}/pico_time/include
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5 changes: 5 additions & 0 deletions modules/hal_rpi_pico/Kconfig
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Expand Up @@ -54,3 +54,8 @@ config PICOSDK_USE_RTC
bool
help
Use the RTC driver from pico-sdk

config PICOSDK_USE_RAND
bool
help
Use the "rand" driver from pico-sdk
4 changes: 4 additions & 0 deletions modules/hal_rpi_pico/uninit_data.ld
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@dsseng dsseng Aug 16, 2025

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Why is this required? Maybe SDK functions using this could be avoided?

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@xudongzheng xudongzheng Aug 18, 2025

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Pico SDK mixes the TRNG output with uninitialized memory: https://github.com/raspberrypi/pico-sdk/blob/a1438dff1d38bd9c65dbd693f0e5db4b9ae91779/src/rp2_common/pico_rand/rand.c#L365-L374

To work around that, one would have to use capture_additional_trng_samples(), but that's not public API.

Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
.uninitialized_data (NOLOAD): {

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modules/hal_rpi_pico/uninit_data.ld:1 File has no SPDX-FileCopyrightText header, consider adding one.

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. = ALIGN(4);
*(.uninitialized_data*)
} > RAM
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