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arch/arm/rp23xx: Add hardware TRNG driver for /dev/random.
Add a driver for the rp2350 hardware true random number generator. Enabling CONFIG_RP23XX_RNG selects ARCH_HAVE_RNG and builds the driver, which registers /dev/random (and /dev/urandom when CONFIG_DEV_URANDOM selects the architecture source, DEV_URANDOM_ARCH). Each read enables the entropy source, waits for a valid 192-bit entropy holding register (EHR) sample, reads the six 32-bit EHR words, and repeats until the request is satisfied. Document the TRNG on the rp23xx platform page. Assisted-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
This commit is contained in:
Marco Casaroli
Xiang Xiao
parent
aa3157e234
commit
52e84e0c0a
6 changed files with 222 additions and 0 deletions
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@ -26,6 +26,7 @@ ignore-words-list =
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BU,
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DAA,
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dout,
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ehr,
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emac,
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eeeprom,
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extint,
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@ -41,6 +41,7 @@ Flash ROM Boot Working Does not require boot2 from pico-sdk
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If picotool is available a nuttx.uf2 file will be created
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SRAM Boot Working Requires external SWD debugger
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PSRAM Working Three modes of heap allocation described below
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TRNG Working Hardware RNG at /dev/random and /dev/urandom
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============== ============ =====
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Installation
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@ -203,6 +204,24 @@ GPIO 0 and 1 pins must be connected to the device such as USB-serial converter.
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The `usbnsh` configuration provides the console access by USB CDC/ACM serial
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device. The console is available by using a terminal software on the USB host.
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TRNG
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====
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The rp2350 has a hardware true random number generator (TRNG). Enabling
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``RP23XX_RNG`` builds the driver and selects ``ARCH_HAVE_RNG``, which in turn
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makes ``DEV_RANDOM`` available.
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With ``DEV_RANDOM`` enabled the driver registers ``/dev/random``. Enabling
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``DEV_URANDOM`` additionally registers ``/dev/urandom``; when a hardware RNG is
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present the architecture source (``DEV_URANDOM_ARCH``) is selected by default,
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so ``/dev/urandom`` is served from the same TRNG rather than a software PRNG.
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Each read collects entropy from the TRNG's 192-bit entropy holding register
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(EHR): the source is enabled, the driver waits for ``TRNG_VALID``, reads the
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six 32-bit EHR words, and repeats until the request is satisfied. For example::
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nsh> dd if=/dev/random of=/dev/console bs=16 count=1
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Supported Boards
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================
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@ -60,6 +60,10 @@ if(CONFIG_RP23XX_I2C)
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list(APPEND SRCS rp23xx_i2c.c)
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endif()
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if(CONFIG_RP23XX_RNG)
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list(APPEND SRCS rp23xx_rng.c)
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endif()
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if(CONFIG_RP23XX_I2C_SLAVE)
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list(APPEND SRCS rp23xx_i2c_slave.c)
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endif()
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@ -740,6 +740,15 @@ endif # SPISD Configuration
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# ADC Configuration
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#####################################################################
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config RP23XX_RNG
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bool "Enable hardware TRNG (/dev/random)"
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default n
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select ARCH_HAVE_RNG
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---help---
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Enable the RP2350 hardware true random number generator. Provides
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/dev/random (and /dev/urandom when CONFIG_DEV_URANDOM selects the
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architecture source) via the TRNG entropy register (EHR).
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config RP23XX_ADC
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bool "Enable ADC Support"
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default n
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@ -64,6 +64,10 @@ ifeq ($(CONFIG_RP23XX_I2C),y)
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CHIP_CSRCS += rp23xx_i2c.c
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endif
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ifeq ($(CONFIG_RP23XX_RNG),y)
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CHIP_CSRCS += rp23xx_rng.c
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endif
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ifeq ($(CONFIG_RP23XX_I2C_SLAVE),y)
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CHIP_CSRCS += rp23xx_i2c_slave.c
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endif
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185
arch/arm/src/rp23xx/rp23xx_rng.c
Normal file
185
arch/arm/src/rp23xx/rp23xx_rng.c
Normal file
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@ -0,0 +1,185 @@
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/****************************************************************************
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* arch/arm/src/rp23xx/rp23xx_rng.c
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <sys/types.h>
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#include <stdint.h>
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#include <string.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <nuttx/fs/fs.h>
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#include <nuttx/mutex.h>
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#include <nuttx/drivers/drivers.h>
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#include "arm_internal.h"
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#include "hardware/rp23xx_trng.h"
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#if defined(CONFIG_DEV_RANDOM) || defined(CONFIG_DEV_URANDOM_ARCH)
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/* The TRNG delivers entropy 192 bits (six 32-bit EHR words) at a time. */
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#define RP23XX_TRNG_EHR_WORDS 6
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#define RP23XX_TRNG_EHR_BYTES (RP23XX_TRNG_EHR_WORDS * sizeof(uint32_t))
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/* TRNG_VALID.EHR_VALID: the EHR holds a fresh 192-bit sample. */
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#define RP23XX_TRNG_EHR_VALID (1 << 0)
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/****************************************************************************
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* Private Function Prototypes
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****************************************************************************/
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static ssize_t rp23xx_rng_read(struct file *filep, char *buffer,
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size_t buflen);
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/****************************************************************************
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* Private Data
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****************************************************************************/
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static mutex_t g_rng_lock = NXMUTEX_INITIALIZER;
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static const struct file_operations g_rngops =
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{
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NULL, /* open */
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NULL, /* close */
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rp23xx_rng_read, /* read */
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NULL, /* write */
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NULL, /* seek */
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NULL, /* ioctl */
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};
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Name: rp23xx_rng_read
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*
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* Description:
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* Fill 'buffer' with 'buflen' bytes of hardware entropy. Enables the ring
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* -oscillator source, then repeatedly waits for a valid 192-bit EHR and
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* copies it out until the request is satisfied.
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*
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****************************************************************************/
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static ssize_t rp23xx_rng_read(struct file *filep, char *buffer,
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size_t buflen)
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{
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size_t nread = 0;
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int ret;
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ret = nxmutex_lock(&g_rng_lock);
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if (ret < 0)
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{
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return ret;
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}
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/* Enable the entropy source. */
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putreg32(1, RP23XX_TRNG_RND_SOURCE_ENABLE);
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while (nread < buflen)
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{
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uint32_t ehr[RP23XX_TRNG_EHR_WORDS];
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size_t chunk;
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int i;
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/* Wait for the next 192-bit sample to become valid. */
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while ((getreg32(RP23XX_TRNG_TRNG_VALID) & RP23XX_TRNG_EHR_VALID) == 0)
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{
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}
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for (i = 0; i < RP23XX_TRNG_EHR_WORDS; i++)
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{
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ehr[i] = getreg32(RP23XX_TRNG_EHR_DATA(i));
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}
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/* Acknowledge the sample so the engine collects the next one. */
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putreg32(0xffffffff, RP23XX_TRNG_RNG_ICR);
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chunk = buflen - nread;
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if (chunk > RP23XX_TRNG_EHR_BYTES)
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{
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chunk = RP23XX_TRNG_EHR_BYTES;
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}
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memcpy(buffer + nread, ehr, chunk);
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nread += chunk;
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}
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/* Leave the source disabled to save power. */
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putreg32(0, RP23XX_TRNG_RND_SOURCE_ENABLE);
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nxmutex_unlock(&g_rng_lock);
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return (ssize_t)nread;
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: devrandom_register
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*
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* Description:
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* Register /dev/random, backed by the RP2350 hardware TRNG. Called
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* automatically from drivers_initialize() when CONFIG_DEV_RANDOM is set.
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*
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****************************************************************************/
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#ifdef CONFIG_DEV_RANDOM
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void devrandom_register(void)
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{
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register_driver("/dev/random", &g_rngops, 0444, NULL);
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}
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#endif
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/****************************************************************************
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* Name: devurandom_register
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*
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* Description:
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* Register /dev/urandom, backed by the same hardware TRNG. Called from
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* drivers_initialize() when CONFIG_DEV_URANDOM selects the arch source.
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*
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****************************************************************************/
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#ifdef CONFIG_DEV_URANDOM_ARCH
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void devurandom_register(void)
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{
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register_driver("/dev/urandom", &g_rngops, 0444, NULL);
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}
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#endif
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#endif /* CONFIG_DEV_RANDOM || CONFIG_DEV_URANDOM_ARCH */
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