Re: [PATCH v4] rng: Add Turris Mox rTWM RNG driver

[Stefan Roese <sr@denx.de>]

Hi Max,

mostly some nitpicking comments below.

On 2/11/24 14:04, Max Resch wrote:
> A RNG driver for Armada 3720 boards running the Turris Mox rWTM firmware
> from CZ.NIC in the secure processor.
> 
> Signed-off-by: Max Resch <resch.max@gmail.com>
> ---
> 
> Changes in v4:
>   - wrongful/missing git rebase
> 
> Changes in v3:
>   - More meaningful variable names in accordance with review
> 
> Changes in v2:
>   - Removed ring buffer implementation
> 
>   drivers/rng/Kconfig           |   8 +++
>   drivers/rng/Makefile          |   1 +
>   drivers/rng/turris_rwtm_rng.c | 122 ++++++++++++++++++++++++++++++++++
>   3 files changed, 131 insertions(+)
>   create mode 100644 drivers/rng/turris_rwtm_rng.c
> 
> diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
> index a89c899568..cd72852a47 100644
> --- a/drivers/rng/Kconfig
> +++ b/drivers/rng/Kconfig
> @@ -105,4 +105,12 @@ config RNG_JH7110
>   	help
>   	  Enable True Random Number Generator in StarFive JH7110 SoCs.
>   
> +config RNG_TURRIS_RWTM
> +	bool "Turris Mox TRNG in Secure Processor"
> +	depends on DM_RNG && ARMADA_3700
> +	help
> +	  Use TRNG in Turris Mox Secure Processor Firmware. Can be used
> +	  on other Armada-3700 devices (like EspressoBin) if Secure
> +	  Firmware from CZ.NIC is used.
> +
>   endif
> diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
> index 7e64c4cdfc..ecae1a3da3 100644
> --- a/drivers/rng/Makefile
> +++ b/drivers/rng/Makefile
> @@ -17,3 +17,4 @@ obj-$(CONFIG_RNG_SMCCC_TRNG) += smccc_trng.o
>   obj-$(CONFIG_RNG_ARM_RNDR) += arm_rndr.o
>   obj-$(CONFIG_TPM_RNG) += tpm_rng.o
>   obj-$(CONFIG_RNG_JH7110) += jh7110_rng.o
> +obj-$(CONFIG_RNG_TURRIS_RWTM) += turris_rwtm_rng.o
> diff --git a/drivers/rng/turris_rwtm_rng.c b/drivers/rng/turris_rwtm_rng.c
> new file mode 100644
> index 0000000000..ec2cb0bca3
> --- /dev/null
> +++ b/drivers/rng/turris_rwtm_rng.c
> @@ -0,0 +1,122 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later OR BSD-3-Clause
> +/*
> + * Copyright (c) 2024, Max Resch
> + */
> +
> +#include <dm.h>
> +#include <malloc.h>
> +#include <rng.h>
> +#include <asm/dma-mapping.h>
> +#include <asm/types.h>
> +#include <mach/mbox.h>
> +
> +/* size of entropy buffer */
> +#define RNG_BUFFER_SIZE	128U
> +
> +struct turris_rwtm_rng_priv {
> +	phys_addr_t buffer;
> +};
> +
> +static int turris_rwtm_rng_fill_entropy(phys_addr_t entropy, size_t size)
> +{
> +	u32 args[3] = { 1, (u32)entropy, size };
> +	int ret;
> +
> +	/* flush data cache */
> +	flush_dcache_range(entropy, entropy + size);
> +
> +	/*
> +	 * get entropy
> +	 * args[0] = 1 copies BYTES array in args[1] of length args[2]
> +	 */
> +	ret = mbox_do_cmd(MBOX_CMD_GET_RANDOM, args, 3, NULL, 0);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* invalidate data cache */
> +	invalidate_dcache_range(entropy, entropy + size);
> +
> +	return 0;
> +}
> +
> +static int turris_rwtm_rng_random_read(struct udevice *dev, void *data, size_t count)
> +{
> +	struct turris_rwtm_rng_priv *priv = dev_get_priv(dev);
> +	phys_addr_t phys;
> +	size_t size;
> +	int ret;
> +
> +	phys = priv->buffer;
> +
> +	while (count) {
> +		size = min_t(size_t, RNG_BUFFER_SIZE, count);
> +
> +		ret = turris_rwtm_rng_fill_entropy(phys, size);

Return code check missing here.

> +
> +		memcpy(data, (void *)phys, size);
> +		count -= size;
> +		data = (u8 *)data + size;
> +	}
> +
> +	return 0;
> +}
> +
> +static int turris_rwtm_rng_probe(struct udevice *dev)
> +{
> +	struct turris_rwtm_rng_priv *priv = dev_get_priv(dev);
> +	u32 args[] = { 0 };
> +	int ret;
> +
> +	/*
> +	 * check if the random command is supported
> +	 * args[0] = 0 would copy 16 DWORDS entropy to out but we ignore them
> +	 */
> +	ret = mbox_do_cmd(MBOX_CMD_GET_RANDOM, args, ARRAY_SIZE(args), NULL, 0);
> +

Please drop this empty line before the ret check.

> +	if (ret < 0)
> +		return ret;
> +
> +	/* entropy buffer */
> +	priv->buffer = 0;
> +
> +	/* buffer address need to be aligned */
> +	dma_alloc_coherent(RNG_BUFFER_SIZE, (unsigned long *)&priv->buffer);
> +	if (!priv->buffer)
> +		return -ENOMEM;
> +
> +	return 0;
> +}
> +
> +static int turris_rwtm_rng_remove(struct udevice *dev)
> +{
> +	struct turris_rwtm_rng_priv *priv = dev_get_priv(dev);
> +	phys_addr_t phys = priv->buffer;
> +
> +	dma_free_coherent((void *)phys);
> +
> +	return 0;
> +}
> +
> +static const struct dm_rng_ops turris_rwtm_rng_ops = {
> +	.read = turris_rwtm_rng_random_read,
> +};
> +
> +/*
> + * only Turris MOX firmware has the RNG but allow all probable devices to be
> + * probed the default firmware will just reject the probe
> + */
> +static const struct udevice_id turris_rwtm_rng_match[] = {
> +	{ .compatible = "cznic,turris-mox-rwtm" },
> +	{ .compatible = "marvell,armada-3700-rwtm-firmware" },
> +	{},
> +};
> +
> +U_BOOT_DRIVER(turris_rwtm_rng) = {
> +	.name	= "turris-rwtm-rng",
> +	.id	= UCLASS_RNG,
> +	.of_match = turris_rwtm_rng_match,
> +	.ops	= &turris_rwtm_rng_ops,
> +	.probe	= turris_rwtm_rng_probe,
> +	.remove = turris_rwtm_rng_remove,
> +	.priv_auto = sizeof(struct turris_rwtm_rng_priv),
> +};

Thanks,
Stefan