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/*
* Copyright (c) 2015, Daniel Thompson
*
* This file is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This file is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#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_address.h>
#include <linux/of_platform.h>
#include <linux/pm_runtime.h>
#include <linux/slab.h>
#define RNG_CR 0x00
#define RNG_CR_RNGEN BIT(2)
#define RNG_SR 0x04
#define RNG_SR_SEIS BIT(6)
#define RNG_SR_CEIS BIT(5)
#define RNG_SR_DRDY BIT(0)
#define RNG_DR 0x08
/*
* It takes 40 cycles @ 48MHz to generate each random number (e.g. <1us).
* At the time of writing STM32 parts max out at ~200MHz meaning a timeout
* of 500 leaves us a very comfortable margin for error. The loop to which
* the timeout applies takes at least 4 instructions per iteration so the
* timeout is enough to take us up to multi-GHz parts!
*/
#define RNG_TIMEOUT 500
struct stm32_rng_private {
struct hwrng rng;
void __iomem *base;
struct clk *clk;
};
static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
struct stm32_rng_private *priv =
container_of(rng, struct stm32_rng_private, rng);
u32 sr;
int retval = 0;
pm_runtime_get_sync((struct device *) priv->rng.priv);
while (max > sizeof(u32)) {
sr = readl_relaxed(priv->base + RNG_SR);
if (!sr && wait) {
unsigned int timeout = RNG_TIMEOUT;
do {
cpu_relax();
sr = readl_relaxed(priv->base + RNG_SR);
} while (!sr && --timeout);
}
/* If error detected or data not ready... */
if (sr != RNG_SR_DRDY)
break;
*(u32 *)data = readl_relaxed(priv->base + RNG_DR);
retval += sizeof(u32);
data += sizeof(u32);
max -= sizeof(u32);
}
if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS),
"bad RNG status - %x\n", sr))
writel_relaxed(0, priv->base + RNG_SR);
pm_runtime_mark_last_busy((struct device *) priv->rng.priv);
pm_runtime_put_sync_autosuspend((struct device *) priv->rng.priv);
return retval || !wait ? retval : -EIO;
}
static int stm32_rng_init(struct hwrng *rng)
{
struct stm32_rng_private *priv =
container_of(rng, struct stm32_rng_private, rng);
int err;
err = clk_prepare_enable(priv->clk);
if (err)
return err;
writel_relaxed(RNG_CR_RNGEN, priv->base + RNG_CR);
/* clear error indicators */
writel_relaxed(0, priv->base + RNG_SR);
return 0;
}
static void stm32_rng_cleanup(struct hwrng *rng)
{
struct stm32_rng_private *priv =
container_of(rng, struct stm32_rng_private, rng);
writel_relaxed(0, priv->base + RNG_CR);
clk_disable_unprepare(priv->clk);
}
static int stm32_rng_probe(struct platform_device *ofdev)
{
struct device *dev = &ofdev->dev;
struct device_node *np = ofdev->dev.of_node;
struct stm32_rng_private *priv;
struct resource res;
int err;
priv = devm_kzalloc(dev, sizeof(struct stm32_rng_private), GFP_KERNEL);
if (!priv)
return -ENOMEM;
err = of_address_to_resource(np, 0, &res);
if (err)
return err;
priv->base = devm_ioremap_resource(dev, &res);
if (IS_ERR(priv->base))
return PTR_ERR(priv->base);
priv->clk = devm_clk_get(&ofdev->dev, NULL);
if (IS_ERR(priv->clk))
return PTR_ERR(priv->clk);
dev_set_drvdata(dev, priv);
priv->rng.name = dev_driver_string(dev),
#ifndef CONFIG_PM
priv->rng.init = stm32_rng_init,
priv->rng.cleanup = stm32_rng_cleanup,
#endif
priv->rng.read = stm32_rng_read,
priv->rng.priv = (unsigned long) dev;
pm_runtime_set_autosuspend_delay(dev, 100);
pm_runtime_use_autosuspend(dev);
pm_runtime_enable(dev);
return devm_hwrng_register(dev, &priv->rng);
}
#ifdef CONFIG_PM
static int stm32_rng_runtime_suspend(struct device *dev)
{
struct stm32_rng_private *priv = dev_get_drvdata(dev);
stm32_rng_cleanup(&priv->rng);
return 0;
}
static int stm32_rng_runtime_resume(struct device *dev)
{
struct stm32_rng_private *priv = dev_get_drvdata(dev);
return stm32_rng_init(&priv->rng);
}
#endif
static UNIVERSAL_DEV_PM_OPS(stm32_rng_pm_ops, stm32_rng_runtime_suspend,
stm32_rng_runtime_resume, NULL);
static const struct of_device_id stm32_rng_match[] = {
{
.compatible = "st,stm32-rng",
},
{},
};
MODULE_DEVICE_TABLE(of, stm32_rng_match);
static struct platform_driver stm32_rng_driver = {
.driver = {
.name = "stm32-rng",
.pm = &stm32_rng_pm_ops,
.of_match_table = stm32_rng_match,
},
.probe = stm32_rng_probe,
};
module_platform_driver(stm32_rng_driver);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Daniel Thompson <daniel.thompson@linaro.org>");
MODULE_DESCRIPTION("STMicroelectronics STM32 RNG device driver");
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