Re: [PATCH v2 2/2] hwrng: iproc-rng200 - Add Broadcom IPROC RNG driver

[Dmitry Torokhov <dtor@google.com>]

Hi Scott,

On Wed, Feb 25, 2015 at 10:16:24AM -0800, Scott Branden wrote:
> This adds a driver for random number generator present on Broadcom
> IPROC devices.
> 
> Reviewed-by: Ray Jui <rjui@broadcom.com>
> Signed-off-by: Scott Branden <sbranden@broadcom.com>
> ---
>  drivers/char/hw_random/Kconfig        |  13 ++
>  drivers/char/hw_random/Makefile       |   1 +
>  drivers/char/hw_random/iproc-rng200.c | 239 ++++++++++++++++++++++++++++++++++
>  3 files changed, 253 insertions(+)
>  create mode 100644 drivers/char/hw_random/iproc-rng200.c
> 
> diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> index de57b38..f48cf11 100644
> --- a/drivers/char/hw_random/Kconfig
> +++ b/drivers/char/hw_random/Kconfig
> @@ -101,6 +101,19 @@ config HW_RANDOM_BCM2835
>  
>  	  If unsure, say Y.
>  
> +config HW_RANDOM_IPROC_RNG200
> +	tristate "Broadcom iProc RNG200 support"
> +	depends on ARCH_BCM_IPROC
> +	default HW_RANDOM
> +	---help---
> +	  This driver provides kernel-side support for the RNG200
> +	  hardware found on the Broadcom iProc SoCs.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called iproc-rng200
> +
> +	  If unsure, say Y.
> +
>  config HW_RANDOM_GEODE
>  	tristate "AMD Geode HW Random Number Generator support"
>  	depends on X86_32 && PCI
> diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> index 0b4cd57..055bb01 100644
> --- a/drivers/char/hw_random/Makefile
> +++ b/drivers/char/hw_random/Makefile
> @@ -28,5 +28,6 @@ obj-$(CONFIG_HW_RANDOM_POWERNV) += powernv-rng.o
>  obj-$(CONFIG_HW_RANDOM_EXYNOS)	+= exynos-rng.o
>  obj-$(CONFIG_HW_RANDOM_TPM) += tpm-rng.o
>  obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o
> +obj-$(CONFIG_HW_RANDOM_IPROC_RNG200) += iproc-rng200.o
>  obj-$(CONFIG_HW_RANDOM_MSM) += msm-rng.o
>  obj-$(CONFIG_HW_RANDOM_XGENE) += xgene-rng.o
> diff --git a/drivers/char/hw_random/iproc-rng200.c b/drivers/char/hw_random/iproc-rng200.c
> new file mode 100644
> index 0000000..4643aa9
> --- /dev/null
> +++ b/drivers/char/hw_random/iproc-rng200.c
> @@ -0,0 +1,239 @@
> +/*
> +* Copyright (C) 2014 Broadcom Corporation
> +*
> +* This program 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 version 2.
> +*
> +* This program is distributed "as is" WITHOUT ANY WARRANTY of any
> +* kind, whether express or implied; without even the implied warranty
> +* of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +* GNU General Public License for more details.
> +*/
> +/*
> + * DESCRIPTION: The Broadcom iProc RNG200 Driver
> + */
> +
> +#include <linux/hw_random.h>
> +#include <linux/init.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/platform_device.h>
> +#include <linux/delay.h>
> +
> +
> +/* Registers */
> +#define RNG_CTRL_OFFSET					0x00
> +#define RNG_CTRL_RNG_RBGEN_MASK				0x00001FFF
> +#define RNG_CTRL_RNG_RBGEN_ENABLE			0x00000001
> +#define RNG_CTRL_RNG_RBGEN_DISABLE			0x00000000
> +
> +#define RNG_SOFT_RESET_OFFSET				0x04
> +#define RNG_SOFT_RESET_RNG_SOFT_RESET_MASK		0x00000001
> +#define RNG_SOFT_RESET_RNG_SOFT_RESET_ACTIVE		0x00000001
> +#define RNG_SOFT_RESET_RNG_SOFT_RESET_CLEAR		0x00000000
> +
> +#define RBG_SOFT_RESET_OFFSET				0x08
> +#define RBG_SOFT_RESET_RNG_SOFT_RESET_MASK		0x00000001
> +#define RBG_SOFT_RESET_RNG_SOFT_RESET_ACTIVE		0x00000001
> +#define RBG_SOFT_RESET_RNG_SOFT_RESET_CLEAR		0x00000000
> +
> +#define RNG_INT_STATUS_OFFSET				0x18
> +#define RNG_INT_STATUS_MASTER_FAIL_LOCKOUT_IRQ_MASK	0x80000000
> +#define RNG_INT_STATUS_STARTUP_TRANSITIONS_MET_IRQ_MASK	0x00020000
> +#define RNG_INT_STATUS_NIST_FAIL_IRQ_MASK		0x00000020
> +#define RNG_INT_STATUS_TOTAL_BITS_COUNT_IRQ_MASK	0x00000001
> +
> +#define RNG_FIFO_DATA_OFFSET				0x20
> +
> +#define RNG_FIFO_COUNT_OFFSET				0x24
> +#define RNG_FIFO_COUNT_RNG_FIFO_COUNT_MASK		0x000000FF
> +
> +static void iproc_rng200_restart(void __iomem *rng_base)
> +{
> +	uint32_t val;
> +
> +	/* Disable RBG */
> +	val = ioread32(rng_base + RNG_CTRL_OFFSET);
> +	val &= ~RNG_CTRL_RNG_RBGEN_MASK;
> +	val |= RNG_CTRL_RNG_RBGEN_DISABLE;
> +	iowrite32(val, rng_base + RNG_CTRL_OFFSET);
> +
> +	/* Clear all interrupt status */
> +	iowrite32(0xFFFFFFFFUL, rng_base + RNG_INT_STATUS_OFFSET);
> +
> +	/* Reset RNG and RBG */
> +	val = ioread32(rng_base + RBG_SOFT_RESET_OFFSET);
> +	val &= ~RBG_SOFT_RESET_RNG_SOFT_RESET_MASK;
> +	val |= RBG_SOFT_RESET_RNG_SOFT_RESET_ACTIVE;
> +	iowrite32(val, rng_base + RBG_SOFT_RESET_OFFSET);
> +
> +	val = ioread32(rng_base + RNG_SOFT_RESET_OFFSET);
> +	val &= ~RNG_SOFT_RESET_RNG_SOFT_RESET_MASK;
> +	val |= RNG_SOFT_RESET_RNG_SOFT_RESET_ACTIVE;
> +	iowrite32(val, rng_base + RNG_SOFT_RESET_OFFSET);
> +
> +	val = ioread32(rng_base + RNG_SOFT_RESET_OFFSET);
> +	val &= ~RNG_SOFT_RESET_RNG_SOFT_RESET_MASK;
> +	val |= RNG_SOFT_RESET_RNG_SOFT_RESET_CLEAR;
> +	iowrite32(val, rng_base + RNG_SOFT_RESET_OFFSET);
> +
> +	val = ioread32(rng_base + RBG_SOFT_RESET_OFFSET);
> +	val &= ~RBG_SOFT_RESET_RNG_SOFT_RESET_MASK;
> +	val |= RBG_SOFT_RESET_RNG_SOFT_RESET_CLEAR;
> +	iowrite32(val, rng_base + RBG_SOFT_RESET_OFFSET);
> +
> +	/* Enable RBG */
> +	val = ioread32(rng_base + RNG_CTRL_OFFSET);
> +	val &= ~RNG_CTRL_RNG_RBGEN_MASK;
> +	val |= RNG_CTRL_RNG_RBGEN_ENABLE;
> +	iowrite32(val, rng_base + RNG_CTRL_OFFSET);
> +}
> +
> +static int iproc_rng200_read(struct hwrng *rng, void *buf, size_t max,
> +			       bool wait)
> +{
> +	uint32_t status = 0;
> +	uint32_t num_remaining = max;
> +
> +	#define MAX_RESETS_PER_READ	1
> +	uint32_t num_resets = 0;
> +
> +	#define MAX_IDLE_TIME	(1 * HZ)
> +	unsigned long idle_endtime = jiffies + MAX_IDLE_TIME;
> +
> +	/* Retrieve HW RNG registers base address. */
> +	void __iomem *rng_base = (void __iomem *)rng->priv;
> +
> +	while ((num_remaining > 0) && time_before(jiffies, idle_endtime)) {
> +
> +		/* Is RNG sane? If not, reset it. */
> +		status = ioread32(rng_base + RNG_INT_STATUS_OFFSET);
> +		if ((status & (RNG_INT_STATUS_MASTER_FAIL_LOCKOUT_IRQ_MASK |
> +			RNG_INT_STATUS_NIST_FAIL_IRQ_MASK)) != 0) {
> +
> +			if (num_resets >= MAX_RESETS_PER_READ)
> +				return max - num_remaining;
> +
> +			iproc_rng200_restart(rng_base);
> +			num_resets++;
> +		}
> +
> +		/* Are there any random numbers available? */
> +		if ((ioread32(rng_base + RNG_FIFO_COUNT_OFFSET) &
> +				RNG_FIFO_COUNT_RNG_FIFO_COUNT_MASK) > 0) {
> +
> +			if (num_remaining >= sizeof(uint32_t)) {
> +				/* Buffer has room to store entire word */
> +				*(uint32_t *)buf = ioread32(rng_base +
> +							RNG_FIFO_DATA_OFFSET);
> +				buf += sizeof(uint32_t);
> +				num_remaining -= sizeof(uint32_t);
> +			} else {
> +				/* Buffer can only store partial word */
> +				uint32_t rnd_number = ioread32(rng_base +
> +							RNG_FIFO_DATA_OFFSET);
> +				memcpy(buf, &rnd_number, num_remaining);
> +				buf += num_remaining;
> +				num_remaining = 0;
> +			}
> +
> +			/* Reset the IDLE timeout */
> +			idle_endtime = jiffies + MAX_IDLE_TIME;
> +		} else {
> +			if (!wait)
> +				/* Cannot wait, return immediately */
> +				return max - num_remaining;
> +
> +			/* Can wait, give others chance to run */
> +			cpu_relax();
> +		}
> +	}
> +
> +	return max - num_remaining;
> +}
> +
> +static struct hwrng iproc_rng200_ops = {
> +	.name	= "iproc-rng200",
> +	.read	= iproc_rng200_read,
> +};

I would prefer if we allocated a driver-private structure that wraps
hwrng instead of using statically allocated singleton as I wonder how it
will behave if I bind/unbind the device several times.

> +
> +static int iproc_rng200_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	void __iomem *rng_base = 0;
> +	uint32_t val = 0;
> +	int err = 0;

There is no need to initialize all variables as it suppressed "used but
uninitialized" warnings from the compiler. Imagine someone adding a new
init operation and when they handle failure they forget to adjust error
code so it stays 0: for upper layers we'd signal success even though
our device/driver are half-bound.

> +
> +	/* Map peripheral */
> +	struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +
> +	if (!res) {
> +		dev_err(dev, "failed to get rng resources\n");
> +		return -ENODEV;

If we have platform device but it is missing parts of necessary data it
should be -EINVAL.

> +	}
> +
> +	rng_base = devm_ioremap_resource(dev, res);
> +	if (!rng_base) {

devm_ioremap_resource() returns ERR_PTR-encoded result, you need to
check with IS_ERR().

> +		dev_err(dev, "failed to remap rng regs\n");
> +		return -ENODEV;

		return PTR_ERR(rng_base);

> +	}

There is no clock for RNG?

> +
> +	iproc_rng200_ops.priv = (unsigned long)rng_base;
> +
> +	/* Setup RNG. */
> +	val = ioread32(rng_base + RNG_CTRL_OFFSET);
> +	val &= ~RNG_CTRL_RNG_RBGEN_MASK;
> +	val |= RNG_CTRL_RNG_RBGEN_ENABLE;
> +	iowrite32(val, rng_base + RNG_CTRL_OFFSET);

That should be in [new] iproc_rng200_init().

> +
> +	/* Register driver */
> +	err = hwrng_register(&iproc_rng200_ops);
> +	if (err) {
> +		dev_err(dev, "hwrng registration failed\n");
> +		return err;
> +	}
> +	dev_info(dev, "hwrng registered\n");
> +
> +	return 0;
> +}
> +
> +static int iproc_rng200_remove(struct platform_device *pdev)
> +{
> +	uint32_t val = 0;
> +	void __iomem *rng_base = (void __iomem *)iproc_rng200_ops.priv;
> +
> +	/* Unregister driver */
> +	hwrng_unregister(&iproc_rng200_ops);
> +
> +	/* Disable RNG hardware */
> +	val = ioread32(rng_base + RNG_CTRL_OFFSET);
> +	val &= ~RNG_CTRL_RNG_RBGEN_MASK;
> +	val |= RNG_CTRL_RNG_RBGEN_DISABLE;
> +	iowrite32(val, rng_base + RNG_CTRL_OFFSET);

That should be in [new] iproc_rng200_cleanup().

> +
> +	return 0;
> +}
> +

#ifdef CONFIG_OF

maybe?

> +static const struct of_device_id iproc_rng200_of_match[] = {
> +	{ .compatible = "brcm,iproc-rng200", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, iproc_rng200_of_match);
> +
> +static struct platform_driver iproc_rng200_driver = {
> +	.driver = {
> +		.name = "iproc-rng200",
> +		.of_match_table = iproc_rng200_of_match,
> +	},
> +	.probe		= iproc_rng200_probe,
> +	.remove		= iproc_rng200_remove,
> +};
> +module_platform_driver(iproc_rng200_driver);
> +
> +MODULE_AUTHOR("Broadcom");
> +MODULE_DESCRIPTION("iProc RNG200 Random Number Generator driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.3.0
> 

Thanks.

-- 
Dmitry