From: Rick Altherr Subject: [PATCH v1] hw_random: Fix timeriomem_rng for sub-jiffie update periods Date: Tue, 4 Apr 2017 14:43:07 -0700 Message-ID: <20170404214307.7748-1-raltherr@google.com> Cc: openbmc@lists.ozlabs.org, Herbert Xu , Matt Mackall , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: alex@digriz.org.uk Return-path: Received: from mail-pg0-f41.google.com ([74.125.83.41]:35304 "EHLO mail-pg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753363AbdDDVnL (ORCPT ); Tue, 4 Apr 2017 17:43:11 -0400 Received: by mail-pg0-f41.google.com with SMTP id 81so164269248pgh.2 for ; Tue, 04 Apr 2017 14:43:11 -0700 (PDT) Sender: linux-crypto-owner@vger.kernel.org List-ID: 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. Migrated to new hw_random API while I in this driver. Signed-off-by: Rick Altherr --- drivers/char/hw_random/timeriomem-rng.c | 153 ++++++++++++++++---------------- 1 file changed, 75 insertions(+), 78 deletions(-) diff --git a/drivers/char/hw_random/timeriomem-rng.c b/drivers/char/hw_random/timeriomem-rng.c index cf37db263ecd..7482de2ca71c 100644 --- a/drivers/char/hw_random/timeriomem-rng.c +++ b/drivers/char/hw_random/timeriomem-rng.c @@ -20,90 +20,99 @@ * TODO: add support for reading sizes other than 32bits and masking */ -#include -#include -#include -#include +#include +#include +#include #include #include +#include +#include +#include +#include #include +#include #include -#include -#include -#include -#include -struct timeriomem_rng_private_data { +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 timeriomem_rng_ops; + struct hwrng rng_ops; }; -#define to_rng_priv(rng) \ - ((struct timeriomem_rng_private_data *)rng->priv) - -/* - * have data return 1, however return 0 if we have nothing - */ -static int timeriomem_rng_data_present(struct hwrng *rng, int wait) +static int timeriomem_rng_read(struct hwrng *hwrng, void *data, + size_t max, bool wait) { - struct timeriomem_rng_private_data *priv = to_rng_priv(rng); - - if (!wait || priv->present) - return priv->present; + 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); - return 1; -} - -static int timeriomem_rng_data_read(struct hwrng *rng, u32 *data) -{ - struct timeriomem_rng_private_data *priv = to_rng_priv(rng); - unsigned long cur; - s32 delay; - - *data = readl(priv->io_base); - - cur = jiffies; - - delay = cur - priv->expires; - delay = priv->period - (delay % priv->period); - - priv->expires = cur + delay; + 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. + */ 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_data *priv - = (struct timeriomem_rng_private_data *)data; + 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_data *priv; + 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"); + dev_err(&pdev->dev, "timeriomem_rng_private is missing\n"); return -EINVAL; } @@ -119,7 +128,7 @@ static int timeriomem_rng_probe(struct platform_device *pdev) /* Allocate memory for the device structure (and zero it) */ priv = devm_kzalloc(&pdev->dev, - sizeof(struct timeriomem_rng_private_data), GFP_KERNEL); + sizeof(struct timeriomem_rng_private), GFP_KERNEL); if (!priv) return -ENOMEM; @@ -139,54 +148,42 @@ 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); + 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->timeriomem_rng_ops.name = dev_name(&pdev->dev); - priv->timeriomem_rng_ops.data_present = timeriomem_rng_data_present; - priv->timeriomem_rng_ops.data_read = timeriomem_rng_data_read; - priv->timeriomem_rng_ops.priv = (unsigned long)priv; + priv->rng_ops.name = dev_name(&pdev->dev); + priv->rng_ops.read = timeriomem_rng_read; + priv->rng_ops.priv = (unsigned long)priv; 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); } - err = hwrng_register(&priv->timeriomem_rng_ops); + /* 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) { - struct timeriomem_rng_private_data *priv = platform_get_drvdata(pdev); - - hwrng_unregister(&priv->timeriomem_rng_ops); + struct timeriomem_rng_private *priv = platform_get_drvdata(pdev); - del_timer_sync(&priv->timer); + hwrng_unregister(&priv->rng_ops); + hrtimer_cancel(&priv->timer); return 0; } -- 2.12.2.715.g7642488e1d-goog