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

["Marek Behún" <marek.behun@nic.cz>]

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.