diff options
Diffstat (limited to 'drivers/char/hw_random/timeriomem-rng.c')
| -rw-r--r-- | drivers/char/hw_random/timeriomem-rng.c | 205 |
1 files changed, 205 insertions, 0 deletions
diff --git a/drivers/char/hw_random/timeriomem-rng.c b/drivers/char/hw_random/timeriomem-rng.c new file mode 100644 index 0000000000..3db9d868ef --- /dev/null +++ b/drivers/char/hw_random/timeriomem-rng.c @@ -0,0 +1,205 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * drivers/char/hw_random/timeriomem-rng.c + * + * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk> + * + * Derived from drivers/char/hw_random/omap-rng.c + * Copyright 2005 (c) MontaVista Software, Inc. + * Author: Deepak Saxena <dsaxena@plexity.net> + * + * Overview: + * This driver is useful for platforms that have an IO range that provides + * periodic random data from a single IO memory address. All the platform + * has to do is provide the address and 'wait time' that new data becomes + * available. + * + * TODO: add support for reading sizes other than 32bits and masking + */ + +#include <linux/completion.h> +#include <linux/delay.h> +#include <linux/hrtimer.h> +#include <linux/hw_random.h> +#include <linux/io.h> +#include <linux/ktime.h> +#include <linux/module.h> +#include <linux/of.h> +#include <linux/platform_device.h> +#include <linux/slab.h> +#include <linux/time.h> +#include <linux/timeriomem-rng.h> + +struct timeriomem_rng_private { + void __iomem *io_base; + ktime_t period; + unsigned int present:1; + + struct hrtimer timer; + struct completion completion; + + struct hwrng rng_ops; +}; + +static int timeriomem_rng_read(struct hwrng *hwrng, void *data, + size_t max, bool wait) +{ + struct timeriomem_rng_private *priv = + container_of(hwrng, struct timeriomem_rng_private, rng_ops); + int retval = 0; + int period_us = ktime_to_us(priv->period); + + /* + * There may not have been enough time for new data to be generated + * since the last request. If the caller doesn't want to wait, let them + * bail out. Otherwise, wait for the completion. If the new data has + * already been generated, the completion should already be available. + */ + if (!wait && !priv->present) + return 0; + + wait_for_completion(&priv->completion); + + do { + /* + * After the first read, all additional reads will need to wait + * for the RNG to generate new data. Since the period can have + * a wide range of values (1us to 1s have been observed), allow + * for 1% tolerance in the sleep time rather than a fixed value. + */ + if (retval > 0) + usleep_range(period_us, + period_us + max(1, period_us / 100)); + + *(u32 *)data = readl(priv->io_base); + retval += sizeof(u32); + data += sizeof(u32); + max -= sizeof(u32); + } while (wait && max > sizeof(u32)); + + /* + * Block any new callers until the RNG has had time to generate new + * data. + */ + priv->present = 0; + reinit_completion(&priv->completion); + hrtimer_forward_now(&priv->timer, priv->period); + hrtimer_restart(&priv->timer); + + return retval; +} + +static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer) +{ + struct timeriomem_rng_private *priv + = container_of(timer, struct timeriomem_rng_private, timer); + + priv->present = 1; + complete(&priv->completion); + + return HRTIMER_NORESTART; +} + +static int timeriomem_rng_probe(struct platform_device *pdev) +{ + struct timeriomem_rng_data *pdata = pdev->dev.platform_data; + struct timeriomem_rng_private *priv; + struct resource *res; + int err = 0; + int period; + + if (!pdev->dev.of_node && !pdata) { + dev_err(&pdev->dev, "timeriomem_rng_data is missing\n"); + return -EINVAL; + } + + /* Allocate memory for the device structure (and zero it) */ + priv = devm_kzalloc(&pdev->dev, + sizeof(struct timeriomem_rng_private), GFP_KERNEL); + if (!priv) + return -ENOMEM; + + platform_set_drvdata(pdev, priv); + + priv->io_base = devm_platform_get_and_ioremap_resource(pdev, 0, &res); + if (IS_ERR(priv->io_base)) + return PTR_ERR(priv->io_base); + + if (res->start % 4 != 0 || resource_size(res) < 4) { + dev_err(&pdev->dev, + "address must be at least four bytes wide and 32-bit aligned\n"); + return -EINVAL; + } + + if (pdev->dev.of_node) { + int i; + + if (!of_property_read_u32(pdev->dev.of_node, + "period", &i)) + period = i; + else { + dev_err(&pdev->dev, "missing period\n"); + return -EINVAL; + } + + if (!of_property_read_u32(pdev->dev.of_node, + "quality", &i)) + priv->rng_ops.quality = i; + } else { + period = pdata->period; + priv->rng_ops.quality = pdata->quality; + } + + priv->period = ns_to_ktime(period * NSEC_PER_USEC); + init_completion(&priv->completion); + hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); + priv->timer.function = timeriomem_rng_trigger; + + priv->rng_ops.name = dev_name(&pdev->dev); + priv->rng_ops.read = timeriomem_rng_read; + + /* Assume random data is already available. */ + priv->present = 1; + complete(&priv->completion); + + err = devm_hwrng_register(&pdev->dev, &priv->rng_ops); + if (err) { + dev_err(&pdev->dev, "problem registering\n"); + return err; + } + + dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n", + priv->io_base, period); + + return 0; +} + +static int timeriomem_rng_remove(struct platform_device *pdev) +{ + struct timeriomem_rng_private *priv = platform_get_drvdata(pdev); + + hrtimer_cancel(&priv->timer); + + return 0; +} + +static const struct of_device_id timeriomem_rng_match[] = { + { .compatible = "timeriomem_rng" }, + {}, +}; +MODULE_DEVICE_TABLE(of, timeriomem_rng_match); + +static struct platform_driver timeriomem_rng_driver = { + .driver = { + .name = "timeriomem_rng", + .of_match_table = timeriomem_rng_match, + }, + .probe = timeriomem_rng_probe, + .remove = timeriomem_rng_remove, +}; + +module_platform_driver(timeriomem_rng_driver); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>"); +MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver"); |