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// SPDX-License-Identifier: GPL-2.0-only
/*
* ST Random Number Generator Driver ST's Platforms
*
* Author: Pankaj Dev: <pankaj.dev@st.com>
* Lee Jones <lee.jones@linaro.org>
*
* Copyright (C) 2015 STMicroelectronics (R&D) Limited
*/
#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
/* Registers */
#define ST_RNG_STATUS_REG 0x20
#define ST_RNG_DATA_REG 0x24
/* Registers fields */
#define ST_RNG_STATUS_BAD_SEQUENCE BIT(0)
#define ST_RNG_STATUS_BAD_ALTERNANCE BIT(1)
#define ST_RNG_STATUS_FIFO_FULL BIT(5)
#define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */
#define ST_RNG_FIFO_DEPTH 4
#define ST_RNG_FIFO_SIZE (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
/*
* Samples are documented to be available every 0.667us, so in theory
* the 4 sample deep FIFO should take 2.668us to fill. However, during
* thorough testing, it became apparent that filling the FIFO actually
* takes closer to 12us. We then multiply by 2 in order to account for
* the lack of udelay()'s reliability, suggested by Russell King.
*/
#define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2)
struct st_rng_data {
void __iomem *base;
struct hwrng ops;
};
static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
u32 status;
int i;
/* Wait until FIFO is full - max 4uS*/
for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
if (status & ST_RNG_STATUS_FIFO_FULL)
break;
udelay(1);
}
if (i == ST_RNG_FILL_FIFO_TIMEOUT)
return 0;
for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
*(u16 *)(data + i) =
readl_relaxed(ddata->base + ST_RNG_DATA_REG);
return i; /* No of bytes read */
}
static int st_rng_probe(struct platform_device *pdev)
{
struct st_rng_data *ddata;
struct clk *clk;
void __iomem *base;
int ret;
ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
if (!ddata)
return -ENOMEM;
base = devm_platform_ioremap_resource(pdev, 0);
if (IS_ERR(base))
return PTR_ERR(base);
clk = devm_clk_get_enabled(&pdev->dev, NULL);
if (IS_ERR(clk))
return PTR_ERR(clk);
ddata->ops.priv = (unsigned long)ddata;
ddata->ops.read = st_rng_read;
ddata->ops.name = pdev->name;
ddata->base = base;
ret = devm_hwrng_register(&pdev->dev, &ddata->ops);
if (ret) {
dev_err(&pdev->dev, "Failed to register HW RNG\n");
return ret;
}
dev_info(&pdev->dev, "Successfully registered HW RNG\n");
return 0;
}
static const struct of_device_id st_rng_match[] __maybe_unused = {
{ .compatible = "st,rng" },
{},
};
MODULE_DEVICE_TABLE(of, st_rng_match);
static struct platform_driver st_rng_driver = {
.driver = {
.name = "st-hwrandom",
.of_match_table = of_match_ptr(st_rng_match),
},
.probe = st_rng_probe,
};
module_platform_driver(st_rng_driver);
MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
MODULE_DESCRIPTION("ST Microelectronics HW Random Number Generator");
MODULE_LICENSE("GPL v2");
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