diff options
Diffstat (limited to 'drivers/char/hw_random/st-rng.c')
| -rw-r--r-- | drivers/char/hw_random/st-rng.c | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c new file mode 100644 index 000000000..6e9dfac9f --- /dev/null +++ b/drivers/char/hw_random/st-rng.c @@ -0,0 +1,124 @@ +// 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_LICENSE("GPL v2"); |