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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2023, Arm Ltd.
*
* Use the (optional) ARMv8.5 RNDR register to provide random numbers to
* U-Boot's UCLASS_RNG users.
* Detection is done at runtime using the CPU ID registers.
*/
#define LOG_CATEGORY UCLASS_RNG
#include <common.h>
#include <dm.h>
#include <linux/kernel.h>
#include <rng.h>
#include <asm/system.h>
#define DRIVER_NAME "arm-rndr"
static bool cpu_has_rndr(void)
{
uint64_t reg;
__asm__ volatile("mrs %0, ID_AA64ISAR0_EL1\n" : "=r" (reg));
return !!(reg & ID_AA64ISAR0_EL1_RNDR);
}
/*
* The system register name is RNDR, but this isn't widely known among older
* toolchains, and also triggers errors because of it being an architecture
* extension. Since we check the availability of the register before, it's
* fine to use here, though.
*/
#define RNDR "S3_3_C2_C4_0"
static uint64_t read_rndr(void)
{
uint64_t reg;
__asm__ volatile("mrs %0, " RNDR "\n" : "=r" (reg));
return reg;
}
static int arm_rndr_read(struct udevice *dev, void *data, size_t len)
{
uint64_t random;
while (len) {
int tocopy = min(sizeof(uint64_t), len);
random = read_rndr();
memcpy(data, &random, tocopy);
len -= tocopy;
data += tocopy;
}
return 0;
}
static const struct dm_rng_ops arm_rndr_ops = {
.read = arm_rndr_read,
};
static int arm_rndr_probe(struct udevice *dev)
{
if (!cpu_has_rndr())
return -ENODEV;
return 0;
}
U_BOOT_DRIVER(arm_rndr) = {
.name = DRIVER_NAME,
.id = UCLASS_RNG,
.ops = &arm_rndr_ops,
.probe = arm_rndr_probe,
};
U_BOOT_DRVINFO(cpu_arm_rndr) = {
.name = DRIVER_NAME,
};
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