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1// SPDX-License-Identifier: GPL-2.02/*3 * Randomness driver for the ARM SMCCC TRNG Firmware Interface4 * https://developer.arm.com/documentation/den0098/latest/5 *6 * Copyright (C) 2020 Arm Ltd.7 *8 * The ARM TRNG firmware interface specifies a protocol to read entropy9 * from a higher exception level, to abstract from any machine specific10 * implemenations and allow easier use in hypervisors.11 *12 * The firmware interface is realised using the SMCCC specification.13 */14 15#include <linux/bits.h>16#include <linux/device.h>17#include <linux/hw_random.h>18#include <linux/module.h>19#include <linux/platform_device.h>20#include <linux/arm-smccc.h>21 22#ifdef CONFIG_ARM6423#define ARM_SMCCC_TRNG_RND ARM_SMCCC_TRNG_RND6424#define MAX_BITS_PER_CALL (3 * 64UL)25#else26#define ARM_SMCCC_TRNG_RND ARM_SMCCC_TRNG_RND3227#define MAX_BITS_PER_CALL (3 * 32UL)28#endif29 30/* We don't want to allow the firmware to stall us forever. */31#define SMCCC_TRNG_MAX_TRIES 2032 33#define SMCCC_RET_TRNG_INVALID_PARAMETER -234#define SMCCC_RET_TRNG_NO_ENTROPY -335 36static int copy_from_registers(char *buf, struct arm_smccc_res *res,37 size_t bytes)38{39 unsigned int chunk, copied;40 41 if (bytes == 0)42 return 0;43 44 chunk = min(bytes, sizeof(long));45 memcpy(buf, &res->a3, chunk);46 copied = chunk;47 if (copied >= bytes)48 return copied;49 50 chunk = min((bytes - copied), sizeof(long));51 memcpy(&buf[copied], &res->a2, chunk);52 copied += chunk;53 if (copied >= bytes)54 return copied;55 56 chunk = min((bytes - copied), sizeof(long));57 memcpy(&buf[copied], &res->a1, chunk);58 59 return copied + chunk;60}61 62static int smccc_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)63{64 struct arm_smccc_res res;65 u8 *buf = data;66 unsigned int copied = 0;67 int tries = 0;68 69 while (copied < max) {70 size_t bits = min_t(size_t, (max - copied) * BITS_PER_BYTE,71 MAX_BITS_PER_CALL);72 73 arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND, bits, &res);74 75 switch ((int)res.a0) {76 case SMCCC_RET_SUCCESS:77 copied += copy_from_registers(buf + copied, &res,78 bits / BITS_PER_BYTE);79 tries = 0;80 break;81 case SMCCC_RET_TRNG_NO_ENTROPY:82 if (!wait)83 return copied;84 tries++;85 if (tries >= SMCCC_TRNG_MAX_TRIES)86 return copied;87 cond_resched();88 break;89 default:90 return -EIO;91 }92 }93 94 return copied;95}96 97static int smccc_trng_probe(struct platform_device *pdev)98{99 struct hwrng *trng;100 101 trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);102 if (!trng)103 return -ENOMEM;104 105 trng->name = "smccc_trng";106 trng->read = smccc_trng_read;107 108 return devm_hwrng_register(&pdev->dev, trng);109}110 111static struct platform_driver smccc_trng_driver = {112 .driver = {113 .name = "smccc_trng",114 },115 .probe = smccc_trng_probe,116};117module_platform_driver(smccc_trng_driver);118 119MODULE_ALIAS("platform:smccc_trng");120MODULE_AUTHOR("Andre Przywara");121MODULE_DESCRIPTION("Arm SMCCC TRNG firmware interface support");122MODULE_LICENSE("GPL");123