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// SPDX-License-Identifier: GPL-2.0
/* Copyright (C) 2020 Xiphera Ltd. */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/err.h>
#include <linux/io.h>
#include <linux/hw_random.h>
#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/delay.h>
#define CONTROL_REG 0x00000000
#define STATUS_REG 0x00000004
#define RAND_REG 0x00000000
#define HOST_TO_TRNG_RESET 0x00000001
#define HOST_TO_TRNG_RELEASE_RESET 0x00000002
#define HOST_TO_TRNG_ENABLE 0x80000000
#define HOST_TO_TRNG_ZEROIZE 0x80000004
#define HOST_TO_TRNG_ACK_ZEROIZE 0x80000008
#define HOST_TO_TRNG_READ 0x8000000F
/* trng statuses */
#define TRNG_ACK_RESET 0x000000AC
#define TRNG_SUCCESSFUL_STARTUP 0x00000057
#define TRNG_FAILED_STARTUP 0x000000FA
#define TRNG_NEW_RAND_AVAILABLE 0x000000ED
struct xiphera_trng {
void __iomem *mem;
struct hwrng rng;
};
static int xiphera_trng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
{
struct xiphera_trng *trng = container_of(rng, struct xiphera_trng, rng);
int ret = 0;
while (max >= sizeof(u32)) {
/* check for data */
if (readl(trng->mem + STATUS_REG) == TRNG_NEW_RAND_AVAILABLE) {
*(u32 *)buf = readl(trng->mem + RAND_REG);
/*
* Inform the trng of the read
* and re-enable it to produce a new random number
*/
writel(HOST_TO_TRNG_READ, trng->mem + CONTROL_REG);
writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
ret += sizeof(u32);
buf += sizeof(u32);
max -= sizeof(u32);
} else {
break;
}
}
return ret;
}
static int xiphera_trng_probe(struct platform_device *pdev)
{
int ret;
struct xiphera_trng *trng;
struct device *dev = &pdev->dev;
trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
if (!trng)
return -ENOMEM;
trng->mem = devm_platform_ioremap_resource(pdev, 0);
if (IS_ERR(trng->mem))
return PTR_ERR(trng->mem);
/*
* the trng needs to be reset first which might not happen in time,
* hence we incorporate a small delay to ensure proper behaviour
*/
writel(HOST_TO_TRNG_RESET, trng->mem + CONTROL_REG);
usleep_range(100, 200);
if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
/*
* there is a small chance the trng is just not ready yet,
* so we try one more time. If the second time fails, we give up
*/
usleep_range(100, 200);
if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
dev_err(dev, "failed to reset the trng ip\n");
return -ENODEV;
}
}
/*
* once again, to ensure proper behaviour we sleep
* for a while after zeroizing the trng
*/
writel(HOST_TO_TRNG_RELEASE_RESET, trng->mem + CONTROL_REG);
writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
writel(HOST_TO_TRNG_ZEROIZE, trng->mem + CONTROL_REG);
msleep(20);
if (readl(trng->mem + STATUS_REG) != TRNG_SUCCESSFUL_STARTUP) {
/* diagnose the reason for the failure */
if (readl(trng->mem + STATUS_REG) == TRNG_FAILED_STARTUP) {
dev_err(dev, "trng ip startup-tests failed\n");
return -ENODEV;
}
dev_err(dev, "startup-tests yielded no response\n");
return -ENODEV;
}
writel(HOST_TO_TRNG_ACK_ZEROIZE, trng->mem + CONTROL_REG);
trng->rng.name = pdev->name;
trng->rng.read = xiphera_trng_read;
trng->rng.quality = 900;
ret = devm_hwrng_register(dev, &trng->rng);
if (ret) {
dev_err(dev, "failed to register rng device: %d\n", ret);
return ret;
}
platform_set_drvdata(pdev, trng);
return 0;
}
static const struct of_device_id xiphera_trng_of_match[] = {
{ .compatible = "xiphera,xip8001b-trng", },
{},
};
MODULE_DEVICE_TABLE(of, xiphera_trng_of_match);
static struct platform_driver xiphera_trng_driver = {
.driver = {
.name = "xiphera-trng",
.of_match_table = xiphera_trng_of_match,
},
.probe = xiphera_trng_probe,
};
module_platform_driver(xiphera_trng_driver);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Atte Tommiska");
MODULE_DESCRIPTION("Xiphera FPGA-based true random number generator driver");
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