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

[Heinrich Schuchardt]

On 2/13/24 10:16, Stefan Roese wrote:
> 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 at 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 };

On a device with memory above 4 GiB this (u32) conversion may point to a
different location than rwtm_rng_priv.

Is the Armada 3700 family restricted to below 4 GiB?

Should we add a check in the probe function?

Best regards

Heinrich

>> +    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