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: Rick Altherr <raltherr@xxxxxxxxxx>
---
Changes in v2:
- Split performance improvements into separate patch
drivers/char/hw_random/timeriomem-rng.c | 86 +++++++++++++++++----------------
1 file changed, 45 insertions(+), 41 deletions(-)
diff --git a/drivers/char/hw_random/timeriomem-rng.c b/drivers/char/hw_random/timeriomem-rng.c
index 024bdff7999f..a0faa5f05deb 100644
--- a/drivers/char/hw_random/timeriomem-rng.c
+++ b/drivers/char/hw_random/timeriomem-rng.c
@@ -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,
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
* data.
*/
- cur = jiffies;
-
- delay = cur - priv->expires;
- delay = priv->period - (delay % priv->period);
-
- priv->expires = cur + delay;
priv->present = 0;
-
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 *)data;
+ = 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)
@@ -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);
init_completion(&priv->completion);
- complete(&priv->completion);
-
- 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->rng_ops.name = dev_name(&pdev->dev);
priv->rng_ops.read = 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;
+ complete(&priv->completion);
+
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;
-
-out_timer:
- del_timer_sync(&priv->timer);
- 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);
hwrng_unregister(&priv->rng_ops);
-
- del_timer_sync(&priv->timer);
+ hrtimer_cancel(&priv->timer);
return 0;
}
--
2.12.2.715.g7642488e1d-goog
