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