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badef4cd4a
In different parts of our code we assume that the first RNG device is the
one to be used. Therefore it is preferable to detect the availability of
the RNDR register already in the bind method.
For signaling the non-existence of a device the driver model requires using
ENOENT (and not ENODEV).
Fixes: 31565bb0aa ("driver: rng: Add DM_RNG interface for ARMv8.5 RNDR registers")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Andre Przywara <andre.przywara@arm.com>
82 lines
1.6 KiB
C
82 lines
1.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (c) 2023, Arm Ltd.
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*
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* Use the (optional) ARMv8.5 RNDR register to provide random numbers to
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* U-Boot's UCLASS_RNG users.
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* Detection is done at runtime using the CPU ID registers.
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*/
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#define LOG_CATEGORY UCLASS_RNG
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#include <common.h>
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#include <dm.h>
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#include <linux/kernel.h>
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#include <rng.h>
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#include <asm/system.h>
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#define DRIVER_NAME "arm-rndr"
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static bool cpu_has_rndr(void)
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{
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uint64_t reg;
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__asm__ volatile("mrs %0, ID_AA64ISAR0_EL1\n" : "=r" (reg));
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return !!(reg & ID_AA64ISAR0_EL1_RNDR);
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}
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/*
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* The system register name is RNDR, but this isn't widely known among older
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* toolchains, and also triggers errors because of it being an architecture
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* extension. Since we check the availability of the register before, it's
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* fine to use here, though.
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*/
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#define RNDR "S3_3_C2_C4_0"
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static uint64_t read_rndr(void)
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{
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uint64_t reg;
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__asm__ volatile("mrs %0, " RNDR "\n" : "=r" (reg));
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return reg;
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}
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static int arm_rndr_read(struct udevice *dev, void *data, size_t len)
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{
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uint64_t random;
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while (len) {
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int tocopy = min(sizeof(uint64_t), len);
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random = read_rndr();
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memcpy(data, &random, tocopy);
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len -= tocopy;
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data += tocopy;
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}
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return 0;
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}
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static const struct dm_rng_ops arm_rndr_ops = {
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.read = arm_rndr_read,
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};
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static int arm_rndr_bind(struct udevice *dev)
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{
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if (!cpu_has_rndr())
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return -ENOENT;
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return 0;
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}
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U_BOOT_DRIVER(arm_rndr) = {
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.name = DRIVER_NAME,
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.id = UCLASS_RNG,
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.ops = &arm_rndr_ops,
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.bind = arm_rndr_bind,
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};
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U_BOOT_DRVINFO(cpu_arm_rndr) = {
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.name = DRIVER_NAME,
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};
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