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Date: Wed, 3 Feb 2016 11:22:53 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Joshua Henderson <joshua.henderson@...rochip.com>,
linux-kernel@...r.kernel.org
Cc: linux-mips@...ux-mips.org,
Purna Chandra Mandal <purna.mandal@...rochip.com>,
Matt Mackall <mpm@...enic.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
Kieran Bingham <kieranbingham@...il.com>,
Lee Jones <lee.jones@...aro.org>,
Pankaj Dev <pankaj.dev@...com>,
Scott Branden <sbranden@...adcom.com>,
Ray Jui <rjui@...adcom.com>, linux-crypto@...r.kernel.org
Subject: Re: [PATCH 2/2] rng: pic32-rng: Add PIC32 RNG hardware driver
On 01/02/16 22:41, Joshua Henderson wrote:
> Add support for the hardware pseudo and true random number generator
> peripheral found on PIC32.
>
> Signed-off-by: Joshua Henderson <joshua.henderson@...rochip.com>
> Signed-off-by: Purna Chandra Mandal <purna.mandal@...rochip.com>
> ---
> drivers/char/hw_random/Kconfig | 13 +++
> drivers/char/hw_random/Makefile | 1 +
> drivers/char/hw_random/pic32-rng.c | 152 ++++++++++++++++++++++++++++++++++++
> 3 files changed, 166 insertions(+)
> create mode 100644 drivers/char/hw_random/pic32-rng.c
>
> diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> index dbf2271..3ab0c46 100644
> --- a/drivers/char/hw_random/Kconfig
> +++ b/drivers/char/hw_random/Kconfig
> @@ -381,6 +381,19 @@ config HW_RANDOM_STM32
>
> If unsure, say N.
>
> +config HW_RANDOM_PIC32
> + tristate "Microchip PIC32 Random Number Generator support"
> + depends on HW_RANDOM && MACH_PIC32
> + default y
> + ---help---
> + This driver provides kernel-side support for the Random Number
> + Generator hardware found on a PIC32.
> +
> + To compile this driver as a module, choose M here. the
> + module will be called pic32-rng.
> +
> + If unsure, say Y.
> +
> endif # HW_RANDOM
>
> config UML_RANDOM
> diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> index 5ad3976..f5a6fa7 100644
> --- a/drivers/char/hw_random/Makefile
> +++ b/drivers/char/hw_random/Makefile
> @@ -33,3 +33,4 @@ obj-$(CONFIG_HW_RANDOM_MSM) += msm-rng.o
> obj-$(CONFIG_HW_RANDOM_ST) += st-rng.o
> obj-$(CONFIG_HW_RANDOM_XGENE) += xgene-rng.o
> obj-$(CONFIG_HW_RANDOM_STM32) += stm32-rng.o
> +obj-$(CONFIG_HW_RANDOM_PIC32) += pic32-rng.o
> diff --git a/drivers/char/hw_random/pic32-rng.c b/drivers/char/hw_random/pic32-rng.c
> new file mode 100644
> index 0000000..d2f32c4
> --- /dev/null
> +++ b/drivers/char/hw_random/pic32-rng.c
> @@ -0,0 +1,152 @@
> +/*
> + * PIC32 RNG driver
> + *
> + * Joshua Henderson <joshua.henderson@...rochip.com>
> + * Copyright (C) 2016 Microchip Technology Inc. All rights reserved.
> + *
> + * This program is free software; you can distribute it and/or modify it
> + * under the terms of the GNU General Public License (Version 2) as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
> + * for more details.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/delay.h>
> +#include <linux/slab.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/hw_random.h>
> +#include <linux/platform_device.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/clk.h>
> +#include <linux/clkdev.h>
> +
> +#define RNGCON 0x04
> +#define TRNGEN BIT(8)
> +#define PRNGEN BIT(9)
> +#define PRNGCONT BIT(10)
> +#define TRNGMOD BIT(11)
> +#define SEEDLOAD BIT(12)
> +#define RNGPOLY1 0x08
> +#define RNGPOLY2 0x0C
> +#define RNGNUMGEN1 0x10
> +#define RNGNUMGEN2 0x14
> +#define RNGSEED1 0x18
> +#define RNGSEED2 0x1C
> +#define RNGRCNT 0x20
> +#define RCNT_MASK 0x7F
> +
> +struct pic32_rng {
> + void __iomem *base;
> + struct hwrng rng;
> + struct clk *clk;
> +};
> +
> +static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
> + bool wait)
> +{
> + struct pic32_rng *prng = container_of(rng, struct pic32_rng, rng);
> + u64 *data = buf;
> +
> + *data = ((u64)readl(prng->base + RNGNUMGEN2) << 32) +
> + readl(prng->base + RNGNUMGEN1);
> + return 4;
> +}
I have a number of questions at this point (although #3 is by far the
most important).
1. If the random number of 42-bit shouldn't this be return 5; ?
2. If you really do mean return 4; then why mess about with all the
shifting. You can just read and discard the upper 32-bits.
3. Why are you using the PRNG at all? The PRNG is a simple LSFR and
I don't think it ever gets reseeded at any point (meaning we get
almost no useful entropy from it at all).
Far better to read directly from the TRNG.
> +
> +static int pic32_rng_probe(struct platform_device *pdev)
> +{
> + struct pic32_rng *prng;
> + struct resource *res;
> + u32 v, t;
> + int ret;
> +
> + prng = devm_kzalloc(&pdev->dev, sizeof(*prng), GFP_KERNEL);
> + if (!prng)
> + return -ENOMEM;
> +
> + res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> + prng->base = devm_ioremap_resource(&pdev->dev, res);
> + if (IS_ERR(prng->base))
> + return PTR_ERR(prng->base);
> +
> + prng->clk = devm_clk_get(&pdev->dev, NULL);
> + if (IS_ERR(prng->clk))
> + return PTR_ERR(prng->clk);
> +
> + clk_prepare_enable(prng->clk);
> +
> + /* enable TRNG in enhanced mode */
> + v = readl(prng->base + RNGCON);
> + v &= ~(TRNGEN | PRNGEN | 0xff);
> + v |= TRNGMOD;
> + writel(v | TRNGEN, prng->base + RNGCON);
> +
> + /* wait for valid seed */
> + usleep_range(100, 200);
> + t = readl(prng->base + RNGRCNT) & RCNT_MASK;
> + if (t < 0x2A)
> + dev_warn(&pdev->dev, "seed not generated.\n");
> +
> + /* load initial seed */
> + writel(v | SEEDLOAD, prng->base + RNGCON);
> +
> + /* load initial polynomial: 42bit poly */
> + writel(0x00c00003, prng->base + RNGPOLY1);
> + writel(0x00000000, prng->base + RNGPOLY2);
> +
> + /* start PRNG to generate 42bit random */
> + v |= 0x2A | PRNGCONT | PRNGEN;
> + writel(v, prng->base + RNGCON);
> +
> + prng->rng.name = pdev->name;
> + prng->rng.read = pic32_rng_read;
> +
> + ret = hwrng_register(&prng->rng);
> + if (ret)
> + goto err_register;
> +
> + platform_set_drvdata(pdev, prng);
> +
> + return 0;
> +
> +err_register:
> + return ret;
Looks like we leak clock references on this error path.
> +
> +static int pic32_rng_remove(struct platform_device *pdev)
> +{
> + struct pic32_rng *rng = platform_get_drvdata(pdev);
> +
> + hwrng_unregister(&rng->rng);
> + writel(0, rng->base + RNGCON);
> + clk_disable_unprepare(rng->clk);
> + return 0;
> +}
> +
> +static const struct of_device_id pic32_rng_of_match[] = {
> + { .compatible = "microchip,pic32mzda-rng", },
> + { /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
> +
> +static struct platform_driver pic32_rng_driver = {
> + .probe = pic32_rng_probe,
> + .remove = pic32_rng_remove,
> + .driver = {
> + .name = "pic32-rng",
> + .owner = THIS_MODULE,
> + .of_match_table = of_match_ptr(pic32_rng_of_match),
> + },
> +};
> +
> +module_platform_driver(pic32_rng_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Joshua Henderson <joshua.henderson@...rochip.com>");
> +MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");
>
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