Commit ca3bff70 authored by Rick Altherr's avatar Rick Altherr Committed by Herbert Xu

hwrng: timeriomem - Improve performance for sub-jiffie update periods

Some hardware RNGs provide a single register for obtaining random data.
Instead of signaling when new data is available, the reader must wait a
fixed amount of time between reads for new data to be generated.
timeriomem_rng implements this scheme with the period specified in
platform data or device tree.  While the period is specified in
microseconds, the implementation used a standard timer which has a
minimum delay of 1 jiffie and caused a significant bottleneck for
devices that can update at 1us.  By switching to an hrtimer, 1us periods
now only delay at most 2us per read.
Signed-off-by: default avatarRick Altherr <>
Signed-off-by: default avatarHerbert Xu <>
parent 5ab693e6
......@@ -21,23 +21,24 @@
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/hrtimer.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/jiffies.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>
#include <linux/timer.h>
struct timeriomem_rng_private {
void __iomem *io_base;
unsigned int expires;
unsigned int period;
ktime_t period;
unsigned int present:1;
struct timer_list timer;
struct hrtimer timer;
struct completion completion;
struct hwrng rng_ops;
......@@ -48,10 +49,13 @@ static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
struct timeriomem_rng_private *priv =
container_of(hwrng, struct timeriomem_rng_private, rng_ops);
unsigned long cur;
s32 delay;
int retval = 0;
int period_us = ktime_to_us(priv->period);
/* The RNG provides 32-bit per read. Ensure there is enough space. */
* The RNG provides 32-bits per read. Ensure there is enough space for
* at minimum one read.
if (max < sizeof(u32))
return 0;
......@@ -66,33 +70,44 @@ static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
*(u32 *)data = readl(priv->io_base);
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)
period_us + min(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.
cur = jiffies;
delay = cur - priv->expires;
delay = priv->period - (delay % priv->period);
priv->expires = cur + delay;
priv->present = 0;
mod_timer(&priv->timer, priv->expires);
hrtimer_forward_now(&priv->timer, priv->period);
return 4;
return retval;
static void timeriomem_rng_trigger(unsigned long data)
static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer)
struct timeriomem_rng_private *priv
= (struct timeriomem_rng_private *)data;
= container_of(timer, struct timeriomem_rng_private, timer);
priv->present = 1;
static int timeriomem_rng_probe(struct platform_device *pdev)
......@@ -140,43 +155,33 @@ static int timeriomem_rng_probe(struct platform_device *pdev)
period = pdata->period;
priv->period = usecs_to_jiffies(period);
if (priv->period < 1) {
dev_err(&pdev->dev, "period is less than one jiffy\n");
return -EINVAL;
priv->expires = jiffies;
priv->present = 1;
priv->period = ns_to_ktime(period * NSEC_PER_USEC);
setup_timer(&priv->timer, timeriomem_rng_trigger, (unsigned long)priv);
hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
priv->timer.function = timeriomem_rng_trigger;
priv-> = dev_name(&pdev->dev);
priv-> = timeriomem_rng_read;
priv->io_base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(priv->io_base)) {
err = PTR_ERR(priv->io_base);
goto out_timer;
return PTR_ERR(priv->io_base);
/* Assume random data is already available. */
priv->present = 1;
err = hwrng_register(&priv->rng_ops);
if (err) {
dev_err(&pdev->dev, "problem registering\n");
goto out_timer;
return err;
dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
priv->io_base, period);
return 0;
return err;
static int timeriomem_rng_remove(struct platform_device *pdev)
......@@ -184,8 +189,7 @@ static int timeriomem_rng_remove(struct platform_device *pdev)
struct timeriomem_rng_private *priv = platform_get_drvdata(pdev);
return 0;
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