Commit ca3bff70 authored by Rick Altherr's avatar Rick Altherr Committed by Herbert Xu
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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 <raltherr@google.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 5ab693e6
...@@ -21,23 +21,24 @@ ...@@ -21,23 +21,24 @@
*/ */
#include <linux/completion.h> #include <linux/completion.h>
#include <linux/delay.h>
#include <linux/hrtimer.h>
#include <linux/hw_random.h> #include <linux/hw_random.h>
#include <linux/io.h> #include <linux/io.h>
#include <linux/jiffies.h> #include <linux/ktime.h>
#include <linux/module.h> #include <linux/module.h>
#include <linux/of.h> #include <linux/of.h>
#include <linux/platform_device.h> #include <linux/platform_device.h>
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/time.h>
#include <linux/timeriomem-rng.h> #include <linux/timeriomem-rng.h>
#include <linux/timer.h>
struct timeriomem_rng_private { struct timeriomem_rng_private {
void __iomem *io_base; void __iomem *io_base;
unsigned int expires; ktime_t period;
unsigned int period;
unsigned int present:1; unsigned int present:1;
struct timer_list timer; struct hrtimer timer;
struct completion completion; struct completion completion;
struct hwrng rng_ops; struct hwrng rng_ops;
...@@ -48,10 +49,13 @@ static int timeriomem_rng_read(struct hwrng *hwrng, void *data, ...@@ -48,10 +49,13 @@ static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
{ {
struct timeriomem_rng_private *priv = struct timeriomem_rng_private *priv =
container_of(hwrng, struct timeriomem_rng_private, rng_ops); container_of(hwrng, struct timeriomem_rng_private, rng_ops);
unsigned long cur; int retval = 0;
s32 delay; 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)) if (max < sizeof(u32))
return 0; return 0;
...@@ -66,33 +70,44 @@ static int timeriomem_rng_read(struct hwrng *hwrng, void *data, ...@@ -66,33 +70,44 @@ static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
wait_for_completion(&priv->completion); wait_for_completion(&priv->completion);
*(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)
usleep_range(period_us,
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 * Block any new callers until the RNG has had time to generate new
* data. * data.
*/ */
cur = jiffies;
delay = cur - priv->expires;
delay = priv->period - (delay % priv->period);
priv->expires = cur + delay;
priv->present = 0; priv->present = 0;
reinit_completion(&priv->completion); reinit_completion(&priv->completion);
mod_timer(&priv->timer, priv->expires); hrtimer_forward_now(&priv->timer, priv->period);
hrtimer_restart(&priv->timer);
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 *priv
= (struct timeriomem_rng_private *)data; = container_of(timer, struct timeriomem_rng_private, timer);
priv->present = 1; priv->present = 1;
complete(&priv->completion); complete(&priv->completion);
return HRTIMER_NORESTART;
} }
static int timeriomem_rng_probe(struct platform_device *pdev) static int timeriomem_rng_probe(struct platform_device *pdev)
...@@ -140,43 +155,33 @@ 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; period = pdata->period;
} }
priv->period = usecs_to_jiffies(period); priv->period = ns_to_ktime(period * NSEC_PER_USEC);
if (priv->period < 1) {
dev_err(&pdev->dev, "period is less than one jiffy\n");
return -EINVAL;
}
priv->expires = jiffies;
priv->present = 1;
init_completion(&priv->completion); init_completion(&priv->completion);
complete(&priv->completion); hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
priv->timer.function = timeriomem_rng_trigger;
setup_timer(&priv->timer, timeriomem_rng_trigger, (unsigned long)priv);
priv->rng_ops.name = dev_name(&pdev->dev); priv->rng_ops.name = dev_name(&pdev->dev);
priv->rng_ops.read = timeriomem_rng_read; priv->rng_ops.read = timeriomem_rng_read;
priv->io_base = devm_ioremap_resource(&pdev->dev, res); priv->io_base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(priv->io_base)) { if (IS_ERR(priv->io_base)) {
err = PTR_ERR(priv->io_base); return PTR_ERR(priv->io_base);
goto out_timer;
} }
/* Assume random data is already available. */
priv->present = 1;
complete(&priv->completion);
err = hwrng_register(&priv->rng_ops); err = hwrng_register(&priv->rng_ops);
if (err) { if (err) {
dev_err(&pdev->dev, "problem registering\n"); dev_err(&pdev->dev, "problem registering\n");
goto out_timer; return err;
} }
dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n", dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
priv->io_base, period); priv->io_base, period);
return 0; return 0;
out_timer:
del_timer_sync(&priv->timer);
return err;
} }
static int timeriomem_rng_remove(struct platform_device *pdev) static int timeriomem_rng_remove(struct platform_device *pdev)
...@@ -184,8 +189,7 @@ 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); struct timeriomem_rng_private *priv = platform_get_drvdata(pdev);
hwrng_unregister(&priv->rng_ops); hwrng_unregister(&priv->rng_ops);
hrtimer_cancel(&priv->timer);
del_timer_sync(&priv->timer);
return 0; return 0;
} }
......
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