501e197a02
The st-rng driver uses devres to register itself with the hwrng core,
the driver will be unregistered from hwrng when its device goes out of
scope. This happens after the driver's remove function is called.
However, st-rng's clock is disabled in the remove function. There's a
short timeframe where st-rng is still registered with the hwrng core
although its clock is disabled. I suppose the clock must be active to
access the hardware and serve requests from the hwrng core.
Switch to devm_clk_get_enabled and let devres disable the clock and
unregister the hwrng. This avoids the race condition.
Fixes: 3e75241be808 ("hwrng: drivers - Use device-managed registration API")
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
125 lines
3.0 KiB
C
125 lines
3.0 KiB
C
// 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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