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

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

[Max Resch]

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);
+
+		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);
+
+	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),
+};
-- 
2.43.0

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

[Stefan Roese]

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

Re: [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@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

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

[Marek Behún]

On Tue, 13 Feb 2024 10:49:43 +0100
Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:

> 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@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?

Indeed it is. Only virtual memory can be mapped to higher locations,
all physical resources (DDR, registers, PCIe, DMA, rWTM) can only be
confiured with 32 bits.

> Should we add a check in the probe function?

No need.