[PATCH 1/1] drivers/rng: add Amlogic hardware RNG driver

[Heinrich Schuchardt <xypron.glpk@gmx.de>]

On 2/26/20 11:51 AM, Sughosh Ganu wrote:
>
> On Tue, 25 Feb 2020 at 03:56, Heinrich Schuchardt <xypron.glpk@gmx.de
> <mailto:xypron.glpk@gmx.de>> wrote:
>
>     Add support for the hardware random number generator of Amlogic SOCs.
>
>     Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de
>     <mailto:xypron.glpk@gmx.de>>
>     ---
>      ?drivers/rng/Kconfig? ? ?|? ?8 +++
>      ?drivers/rng/Makefile? ? |? ?1 +
>      ?drivers/rng/meson-rng.c | 120 ++++++++++++++++++++++++++++++++++++++++
>      ?3 files changed, 129 insertions(+)
>      ?create mode 100644 drivers/rng/meson-rng.c
>
>     diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
>     index c1aa43b823..edb6152bb9 100644
>     --- a/drivers/rng/Kconfig
>     +++ b/drivers/rng/Kconfig
>     @@ -8,6 +8,14 @@ config DM_RNG
>
>      ?if DM_RNG
>
>     +config RNG_MESON
>     +? ? ? ?bool "Amlogic Meson Random Number Generator support"
>     +? ? ? ?depends on ARCH_MESON
>     +? ? ? ?default y
>     +? ? ? ?help
>     +? ? ? ? ?Enable support for hardware random number generator
>     +? ? ? ? ?of Amlogic Meson SoCs.
>     +
>      ?config RNG_SANDBOX
>      ? ? ? ? bool "Sandbox random number generator"
>      ? ? ? ? depends on SANDBOX
>     diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
>     index 3517005541..6a8a66779b 100644
>     --- a/drivers/rng/Makefile
>     +++ b/drivers/rng/Makefile
>     @@ -4,5 +4,6 @@
>      ?#
>
>      ?obj-$(CONFIG_DM_RNG) += rng-uclass.o
>     +obj-$(CONFIG_RNG_MESON) += meson-rng.o
>      ?obj-$(CONFIG_RNG_SANDBOX) += sandbox_rng.o
>      ?obj-$(CONFIG_RNG_STM32MP1) += stm32mp1_rng.o
>     diff --git a/drivers/rng/meson-rng.c b/drivers/rng/meson-rng.c
>     new file mode 100644
>     index 0000000000..4b81a62353
>     --- /dev/null
>     +++ b/drivers/rng/meson-rng.c
>     @@ -0,0 +1,120 @@
>     +// SPDX-License-Identifier: GPL-2.0-or-later
>     +/*
>     + * Copyright 2020, Heinrich Schuchardt <xypron.glpk@gmx.de
>     <mailto:xypron.glpk@gmx.de>>
>     + *
>     + * Driver for Amlogic hardware random number generator
>     + */
>     +
>     +#include <common.h>
>     +#include <clk.h>
>     +#include <dm.h>
>     +#include <rng.h>
>     +#include <asm/io.h>
>     +
>     +struct meson_rng_platdata {
>     +? ? ? ?fdt_addr_t base;
>     +? ? ? ?struct clk clk;
>     +};
>     +
>     +/**
>     + * meson_rng_read() - fill buffer with random bytes
>     + *
>     + * @buffer:? ? buffer to receive data
>     + * @size:? ? ? size of buffer
>     + *
>     + * Return:? ? ?0
>     + */
>     +static int meson_rng_read(struct udevice *dev, void *data, size_t len)
>     +{
>     +? ? ? ?struct meson_rng_platdata *pdata = dev_get_platdata(dev);
>     +? ? ? ?char *buffer = (char *)data;
>     +
>     +? ? ? ?while (len) {
>     +? ? ? ? ? ? ? ?u32 rand = readl(pdata->base);
>     +? ? ? ? ? ? ? ?size_t step;
>
>
> I believe declaration of variables in the middle of the function is
> frowned upon. Can be moved to the start of the function.

rand is defined at the top of the smallest possible code block
delineated by braces.

C compilers before C99 required you to put definitions at the top of
functions. This led to the unsafe coding practice to reuse the same
variable for different purposes in the same function. Currently we are
using -std=gnu11.

U-Boot uses cppcheck in Gitlab CI. Cppcheck gives you a warning if you
could reduce the scope of a variable.

Neither the U-Boot coding style guide
https://www.denx.de/wiki/U-Boot/CodingStyle
nor the Linux kernel coding style guide
https://www.kernel.org/doc/html/v4.10/process/coding-style.html
recommend such unsafe practice.

If you look at other parts of the U-Boot code, you will find that in
lots of places variables are defined in the smallest possible code block
(e.g. fs/fat/fat.c, fs/ext4/ext4_common.c). Due to our legacy we still
carry a lot of code lines not following this rule.

But anyway if you still want it in a different way, I will resubmit.

Best regards

Heinrich

>
> Other than that,
> Reviewed-by: Sughosh Ganu <sughosh.ganu@linaro.org
> <mailto:sughosh.ganu@linaro.org>>
>
> -sughosh
>
>     +
>     +? ? ? ? ? ? ? ?if (len >= 4)
>     +? ? ? ? ? ? ? ? ? ? ? ?step = 4;
>     +? ? ? ? ? ? ? ?else
>     +? ? ? ? ? ? ? ? ? ? ? ?step = len;
>     +? ? ? ? ? ? ? ?memcpy(buffer, &rand, step);
>     +? ? ? ? ? ? ? ?buffer += step;
>     +? ? ? ? ? ? ? ?len -= step;
>     +? ? ? ?}
>     +? ? ? ?return 0;
>     +}
>     +
>     +/**
>     + * meson_rng_probe() - probe rng device
>     + *
>     + * @dev:? ? ? ?device
>     + * Return:? ? ?0 if ok
>     + */
>     +static int meson_rng_probe(struct udevice *dev)
>     +{
>     +? ? ? ?struct meson_rng_platdata *pdata = dev_get_platdata(dev);
>     +? ? ? ?int err;
>     +
>     +? ? ? ?err = clk_enable(&pdata->clk);
>     +? ? ? ?if (err)
>     +? ? ? ? ? ? ? ?return err;
>     +
>     +? ? ? ?return 0;
>     +}
>     +
>     +/**
>     + * meson_rng_remove() - deinitialize rng device
>     + *
>     + * @dev:? ? ? ?device
>     + * Return:? ? ?0 if ok
>     + */
>     +static int meson_rng_remove(struct udevice *dev)
>     +{
>     +? ? ? ?struct meson_rng_platdata *pdata = dev_get_platdata(dev);
>     +
>     +? ? ? ?return clk_disable(&pdata->clk);
>     +}
>     +
>     +/**
>     + * meson_rng_ofdata_to_platdata() - transfer device tree data to
>     plaform data
>     + *
>     + * @dev:? ? ? ?device
>     + * Return:? ? ?0 if ok
>     + */
>     +static int meson_rng_ofdata_to_platdata(struct udevice *dev)
>     +{
>     +? ? ? ?struct meson_rng_platdata *pdata = dev_get_platdata(dev);
>     +? ? ? ?int err;
>     +
>     +? ? ? ?pdata->base = dev_read_addr(dev);
>     +? ? ? ?if (!pdata->base)
>     +? ? ? ? ? ? ? ?return -ENODEV;
>     +
>     +? ? ? ?err = clk_get_by_name(dev, "core", &pdata->clk);
>     +? ? ? ?if (err)
>     +? ? ? ? ? ? ? ?return err;
>     +
>     +? ? ? ?return 0;
>     +}
>     +
>     +static const struct dm_rng_ops meson_rng_ops = {
>     +? ? ? ?.read = meson_rng_read,
>     +};
>     +
>     +static const struct udevice_id meson_rng_match[] = {
>     +? ? ? ?{
>     +? ? ? ? ? ? ? ?.compatible = "amlogic,meson-rng",
>     +? ? ? ?},
>     +? ? ? ?{},
>     +};
>     +
>     +U_BOOT_DRIVER(meson_rng) = {
>     +? ? ? ?.name = "meson-rng",
>     +? ? ? ?.id = UCLASS_RNG,
>     +? ? ? ?.of_match = meson_rng_match,
>     +? ? ? ?.ops = &meson_rng_ops,
>     +? ? ? ?.probe = meson_rng_probe,
>     +? ? ? ?.remove = meson_rng_remove,
>     +? ? ? ?.platdata_auto_alloc_size = sizeof(struct meson_rng_platdata),
>     +? ? ? ?.ofdata_to_platdata = meson_rng_ofdata_to_platdata,
>     +};
>     --
>     2.20.1
>