93d649bd94
Samples are documented to be available every 0.667us, so in theory
the 8 sample deep FIFO should take 5.336us to fill. However, during
thorough testing, it became apparent that filling the FIFO actually
takes closer to 12us.
Also take into consideration that udelay() can behave oddly i.e. not
delay for as long as requested.
Suggested-by: Russell King <rmk+kernel@arm.linux.org.uk>:
"IIRC, Linus recommends a x2 factor on delays, especially
timeouts generated by these functions.
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
151 lines
3.5 KiB
C
151 lines
3.5 KiB
C
/*
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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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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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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/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_FIFO_SIZE 8
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#define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */
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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 clk *clk;
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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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if (max < sizeof(u16))
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return -EINVAL;
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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 resource *res;
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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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res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
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base = devm_ioremap_resource(&pdev->dev, res);
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if (IS_ERR(base))
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return PTR_ERR(base);
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clk = devm_clk_get(&pdev->dev, NULL);
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if (IS_ERR(clk))
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return PTR_ERR(clk);
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ret = clk_prepare_enable(clk);
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if (ret)
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return ret;
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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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ddata->clk = clk;
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dev_set_drvdata(&pdev->dev, ddata);
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ret = hwrng_register(&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 int st_rng_remove(struct platform_device *pdev)
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{
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struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
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hwrng_unregister(&ddata->ops);
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clk_disable_unprepare(ddata->clk);
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return 0;
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}
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static const struct of_device_id st_rng_match[] = {
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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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.remove = st_rng_remove
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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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