Re: [PATCH 2/3] hwrng: exynos - add Samsung Exynos True RNG driver

From: Krzysztof Kozlowski
Date: Thu Nov 23 2017 - 11:31:55 EST

On Thu, Nov 23, 2017 at 4:09 PM, Åukasz Stelmach <l.stelmach@xxxxxxxxxxx> wrote:
> Add support for True Random Number Generator found in Samsung Exynos
> 5250+ SoCs.
>
> Signed-off-by: Åukasz Stelmach <l.stelmach@xxxxxxxxxxx>
> ---
> MAINTAINERS | 7 +
> drivers/char/hw_random/Kconfig | 12 ++
> drivers/char/hw_random/Makefile | 1 +
> drivers/char/hw_random/exynos-trng.c | 256 +++++++++++++++++++++++++++++++++++
> 4 files changed, 276 insertions(+)
> create mode 100644 drivers/char/hw_random/exynos-trng.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2811a211632c..992074cca612 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11780,6 +11780,13 @@ S: Maintained
> F: drivers/crypto/exynos-rng.c
> F: Documentation/devicetree/bindings/rng/samsung,exynos-rng4.txt
>
> +SAMSUNG EXYNOS TRUE RANDOM NUMBER GENERATOR (TRNG) DRIVER
> +M: Åukasz Stelmach <l.stelmach@xxxxxxxxxxx>
> +L: linux-samsung-soc@xxxxxxxxxxxxxxx
> +S: Maintained
> +F: drivers/char/hw_random/exynos-trng.c
> +F: Documentation/devicetree/bindings/rng/samsung,exynos5250-trng.txt
> +
> SAMSUNG FRAMEBUFFER DRIVER
> M: Jingoo Han <jingoohan1@xxxxxxxxx>
> L: linux-fbdev@xxxxxxxxxxxxxxx
> diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> index 95a031e9eced..a788ac07081b 100644
> --- a/drivers/char/hw_random/Kconfig
> +++ b/drivers/char/hw_random/Kconfig
> @@ -449,6 +449,18 @@ config HW_RANDOM_S390
>
> If unsure, say Y.
>
> +config HW_RANDOM_EXYNOS
> + tristate "Samsung Exynos True Random Number Generator support"
> + depends on ARCH_EXYNOS || COMPILE_TEST
> + default HW_RANDOM
> + ---help---
> + This driver provides support for the True Random Number
> + Generator available in Exynos SoCs.
> +
> + To compile this driver as a module, choose M here: the module
> + will be called exynos-trng.
> +
> + If unsure, say Y.
> endif # HW_RANDOM

Thanks for working on TRNG.

1. I was rather thinking about extending existing exynos-rng.c [1] so
it would be using TRNG as seed for PRNG as this gives you much more
random data. Instead you developed totally separate driver which has
its own benefits - one can choose which interface he wants. Although
it is a little bit duplication.

2. I understand that in your current version of TRNG driver there is
no conflict with PRNG and they can work both at the same time?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/crypto/exynos-rng.c

>
> config UML_RANDOM
> diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> index f3728d008fff..5595df97da7a 100644
> --- a/drivers/char/hw_random/Makefile
> +++ b/drivers/char/hw_random/Makefile
> @@ -14,6 +14,7 @@ obj-$(CONFIG_HW_RANDOM_GEODE) += geode-rng.o
> obj-$(CONFIG_HW_RANDOM_N2RNG) += n2-rng.o
> n2-rng-y := n2-drv.o n2-asm.o
> obj-$(CONFIG_HW_RANDOM_VIA) += via-rng.o
> +obj-$(CONFIG_HW_RANDOM_EXYNOS) += exynos-trng.o
> obj-$(CONFIG_HW_RANDOM_IXP4XX) += ixp4xx-rng.o
> obj-$(CONFIG_HW_RANDOM_OMAP) += omap-rng.o
> obj-$(CONFIG_HW_RANDOM_OMAP3_ROM) += omap3-rom-rng.o
> diff --git a/drivers/char/hw_random/exynos-trng.c b/drivers/char/hw_random/exynos-trng.c
> new file mode 100644
> index 000000000000..340e106cae24
> --- /dev/null
> +++ b/drivers/char/hw_random/exynos-trng.c
> @@ -0,0 +1,256 @@
> +/*
> + * RNG driver for Exynos TRNGs
> + *
> + * Author: Åukasz Stelmach <l.stelmach@xxxxxxxxxxx>
> + *
> + * Copyright 2017 (c) Samsung Electronics Software, Inc.
> + *
> + * Based on the Exynos PRNG driver drivers/crypto/exynos-rng by
> + * Krzysztof KozÅowski <krzk@xxxxxxxxxx>
> + *
> + * 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;
> + *
> + * This program is distributed in the hope that 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/clk.h>
> +#include <linux/crypto.h>
> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/hw_random.h>
> +#include <linux/io.h>
> +#include <linux/iopoll.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> +
> +#define EXYNOS_TRNG_CLKDIV (0x0)
> +#define EXYNOS_TRNG_CTRL (0x20)
> +#define EXYNOS_TRNG_POST_CTRL (0x30)
> +#define EXYNOS_TRNG_ONLINE_CTRL (0x40)
> +#define EXYNOS_TRNG_ONLINE_STAT (0x44)
> +#define EXYNOS_TRNG_ONLINE_MAXCHI2 (0x48)
> +#define EXYNOS_TRNG_FIFO_CTRL (0x50)
> +#define EXYNOS_TRNG_FIFO_0 (0x80)
> +#define EXYNOS_TRNG_FIFO_1 (0x84)
> +#define EXYNOS_TRNG_FIFO_2 (0x88)
> +#define EXYNOS_TRNG_FIFO_3 (0x8c)
> +#define EXYNOS_TRNG_FIFO_4 (0x90)
> +#define EXYNOS_TRNG_FIFO_5 (0x94)
> +#define EXYNOS_TRNG_FIFO_6 (0x98)
> +#define EXYNOS_TRNG_FIFO_7 (0x9c)
> +#define EXYNOS_TRNG_FIFO_LEN (8)
> +#define EXYNOS_TRNG_CLOCK_RATE (500000)
> +
> +struct exynos_trng_dev {
> + struct device *dev;
> + void __iomem *mem;
> + struct clk *clk;
> + struct hwrng rng;
> +};
> +
> +struct exynos_trng_dev *exynos_trng_dev;

This definitely should not be globally linked. Also I think this is
not even needed to be file-scope.

> +
> +static inline void exynos_trng_set_reg(struct exynos_trng_dev *trng, u16 reg,
> + u32 val)
> +{
> + /* Check range of reg? */

Is this is a FIXME/TODO note?

> + __raw_writel(val, trng->mem + reg);
> +}
> +
> +static inline u32 exynos_trng_get_reg(struct exynos_trng_dev *trng, u16 reg)
> +{
> + /* Check range of reg? */

Ditto

> + return __raw_readl(trng->mem + reg);
> +}
> +
> +static int exynos_trng_do_read(struct hwrng *rng, void *data, size_t max,
> + bool wait)
> +{
> + struct exynos_trng_dev *trng;
> + u32 val;
> +
> + max = max > (EXYNOS_TRNG_FIFO_LEN * 4) ?
> + (EXYNOS_TRNG_FIFO_LEN * 4) : max;

Maybe use macro min()? This will also nicely point that variable name
"max" is misleading. Max what? Isn't it the size of buffer to read?


> +
> + trng = (struct exynos_trng_dev *)rng->priv;
> +
> + exynos_trng_set_reg(trng, EXYNOS_TRNG_FIFO_CTRL, max * 8);
> + val = readl_poll_timeout(trng->mem + EXYNOS_TRNG_FIFO_CTRL, val,
> + val == 0, 200, 1000000);
> + if (val < 0)
> + return val;
> +
> + memcpy_fromio(data, trng->mem + EXYNOS_TRNG_FIFO_0, max);
> +
> + return max;
> +}
> +
> +static int exynos_trng_init(struct hwrng *rng)
> +{
> + struct exynos_trng_dev *trng;
> + unsigned long sss_rate;
> + u32 val;
> +
> + trng = (struct exynos_trng_dev *)rng->priv;
> + sss_rate = clk_get_rate(trng->clk);
> +
> + /* For most TRNG circuits the clock frequency of under 500 kHz

/* Before actual comment

> + * is safe.
> + */
> + val = sss_rate / (EXYNOS_TRNG_CLOCK_RATE * 2);
> + if (val > 0x7fff) {
> + dev_err(trng->dev, "clock divider too large: %d", val);
> + return -ERANGE;
> + }
> + val = val << 1;
> + exynos_trng_set_reg(trng, EXYNOS_TRNG_CLKDIV, val);
> +
> + /* Enable the generator. */
> + val = 1 << 31;
> + exynos_trng_set_reg(trng, EXYNOS_TRNG_CTRL, val);
> +
> + /* Disable post processing. /dev/hwrng is supposed to deliver
> + * unprocessed data.
> + */

Ditto

> + exynos_trng_set_reg(trng, EXYNOS_TRNG_POST_CTRL, 0);
> +
> + return 0;
> +}
> +
> +static int exynos_trng_probe(struct platform_device *pdev)
> +{
> + struct exynos_trng_dev *trng;
> + struct resource *res;
> + int ret = -ENOMEM;
> +
> + if (exynos_trng_dev)
> + return -EEXIST;
> +
> + trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
> + if (!trng)
> + goto err_ioremap;

No, this should just return with -ENOMEM. Do not print errors on
memory alloc failures.

> +
> + trng->rng.name = devm_kstrdup(&pdev->dev, dev_name(&pdev->dev),
> + GFP_KERNEL);
> + if (!trng->rng.name)
> + goto err_ioremap;

Ditto

> +
> + trng->rng.init = exynos_trng_init;
> + trng->rng.read = exynos_trng_do_read;
> + trng->rng.priv = (unsigned long) trng;
> +
> + platform_set_drvdata(pdev, trng);
> + trng->dev = &pdev->dev;
> +
> + res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> + trng->mem = devm_ioremap_resource(&pdev->dev, res);
> + if (IS_ERR(trng->mem)) {
> + dev_err(&pdev->dev, "Couldn't map IO resources.\n");
> + ret = PTR_ERR(trng->mem);
> + goto err_ioremap;
> + }
> +
> + pm_runtime_enable(&pdev->dev);
> + ret = pm_runtime_get_sync(&pdev->dev);
> + if (ret < 0) {
> + dev_err(&pdev->dev, "pm_runtime_get_sync() failed: %d.\n", ret);
> + goto err_ioremap;

Missing pm_runtime_disable?

> + }
> +
> + trng->clk = devm_clk_get(&pdev->dev, "secss");
> + if (IS_ERR(trng->clk)) {
> + /* XXX: EPROBE_DEFER ? */

TODO note?
If you have questions how to deal with something, ask them. Do not
force reader to rediscover problems you are aware of.

> + dev_err(&pdev->dev, "Couldn't get clock.\n");
> + ret = PTR_ERR(trng->clk);
> + goto err_clock;
> + }
> +
> + ret = clk_prepare_enable(trng->clk);
> + if (ret) {
> + dev_err(&pdev->dev, "Unable to enable the clk: %d.\n", ret);
> + goto err_clock;
> + }
> +
> + ret = hwrng_register(&trng->rng);
> + if (ret) {
> + dev_err(&pdev->dev, "Couldn't register hwrng device.\n");
> + goto err_register;
> + }
> +
> + dev_info(&pdev->dev, "Exynos True Random Number Generator.\n");
> +
> + return 0;
> +
> +err_register:
> + clk_disable_unprepare(trng->clk);
> +
> +err_clock:
> + trng->mem = NULL;

Why this has to be null-ified?

> + pm_runtime_put_sync(&pdev->dev);
> + pm_runtime_disable(&pdev->dev);
> +
> +err_ioremap:
> + dev_err(&pdev->dev, "Initialisation failed.\n");

Double error msg, you already print one before.

Best regards,
Krzysztof