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

[PrasannaKumar Muralidharan]

On 24 November 2017 at 20:55, PrasannaKumar Muralidharan
<prasannatsmkumar@xxxxxxxxx> wrote:
> Hi Lukasz,
>
> Some minor comments below.
>
> On 23 November 2017 at 20:39, 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
>>
>>  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;
>> +
>> +static inline void exynos_trng_set_reg(struct exynos_trng_dev *trng, u16 reg,
>> +                                      u32 val)
>> +{
>> +       /* Check range of reg? */
>> +       __raw_writel(val, trng->mem + reg);
>
> Any specific reason to use __raw_writel? Why not just writel?
>
>> +}
>> +
>> +static inline u32 exynos_trng_get_reg(struct exynos_trng_dev *trng, u16 reg)
>> +{
>> +       /* Check range of reg? */
>> +       return __raw_readl(trng->mem + reg);
>
> Same as above.
>
>> +}
>> +
>> +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;
>
> max is always > 32. This condition is not required.
>
>> +
>> +       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
>> +        * 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.
>> +        */
>> +       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;
>> +
>> +       trng->rng.name = devm_kstrdup(&pdev->dev, dev_name(&pdev->dev),
>> +                                     GFP_KERNEL);
>> +       if (!trng->rng.name)
>> +               goto err_ioremap;
>> +
>> +       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;
>> +       }
>> +
>> +       trng->clk = devm_clk_get(&pdev->dev, "secss");
>> +       if (IS_ERR(trng->clk)) {
>> +               /* XXX: EPROBE_DEFER ? */
>> +               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;
>> +       }
>
> Why not move clk_prepare_enable to init call? While at it please add a
> cleanup callback as well.
>
>> +
>> +       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;
>> +       pm_runtime_put_sync(&pdev->dev);
>> +       pm_runtime_disable(&pdev->dev);
>> +
>> +err_ioremap:
>> +       dev_err(&pdev->dev, "Initialisation failed.\n");
>> +       return ret;
>> +}
>> +
>> +static int exynos_trng_remove(struct platform_device *pdev)
>> +{
>> +       exynos_trng_dev = NULL;
>> +
>> +       return 0;
>> +}
>
> remove is not required as it does not do anything significant.

Should unregister from hwrng in remove callback.

>
>> +
>> +static int __maybe_unused exynos_trng_suspend(struct device *dev)
>> +{
>> +       pm_runtime_put_sync(dev);
>> +
>> +       return 0;
>> +}
>> +
>> +static int __maybe_unused exynos_trng_resume(struct device *dev)
>> +{
>> +       int ret;
>> +
>> +       ret = pm_runtime_get_sync(dev);
>> +       if (ret < 0) {
>> +               dev_err(dev, "pm_runtime_get_sync() failed: %d.\n", ret);
>> +               pm_runtime_put_noidle(dev);
>> +               return ret;
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>> +static SIMPLE_DEV_PM_OPS(exynos_trng_pm_ops, exynos_trng_suspend,
>> +                        exynos_trng_resume);
>> +
>> +static const struct of_device_id exynos_trng_dt_match[] = {
>> +       {
>> +               .compatible = "samsung,exynos5250-trng",
>> +       },
>> +       { },
>> +};
>> +MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);
>> +
>> +static struct platform_driver exynos_trng_driver = {
>> +       .driver = {
>> +               .name = "exynos-trng",
>> +               .pm = &exynos_trng_pm_ops,
>> +               .of_match_table = exynos_trng_dt_match,
>> +       },
>> +       .probe = exynos_trng_probe,
>> +       .remove = exynos_trng_remove,
>> +};
>> +
>> +module_platform_driver(exynos_trng_driver);
>> +MODULE_AUTHOR("Åukasz Stelmach");
>> +MODULE_DESCRIPTION("H/W TRNG driver for Exynos chips");
>> +MODULE_LICENSE("GPL");
>> --
>> 2.11.0
>>
>
> Regards,
> PrasannaKumar