[PATCH v7 2/7] tpm: rng: Add driver model interface for TPM RNG device

[Ilias Apalodimas]

On Wed, 20 Jul 2022 at 15:30, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
>
> The TPM device has a builtin random number generator(RNG)
> functionality. Expose the RNG functions of the TPM device to the
> driver model so that they can be used by the EFI_RNG_PROTOCOL if the
> protocol is installed.
>
> Also change the function arguments and return type of the random
> number functions to comply with the driver model api.
>
> Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> ---
> Changes since V6:
> * Remove the changes made in tpm-v[12].c to return -EIO instead of
>   TPM_LIB_ERROR as suggested by Simon
>
>  drivers/rng/Kconfig   |  9 +++++++++
>  drivers/rng/Makefile  |  1 +
>  drivers/rng/tpm_rng.c | 23 +++++++++++++++++++++++
>  lib/Kconfig           |  1 +
>  lib/tpm_api.c         |  6 +++---
>  5 files changed, 37 insertions(+), 3 deletions(-)
>  create mode 100644 drivers/rng/tpm_rng.c
>
> diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
> index 21a9ff0195..16143681da 100644
> --- a/drivers/rng/Kconfig
> +++ b/drivers/rng/Kconfig
> @@ -74,4 +74,13 @@ config RNG_SMCCC_TRNG
>           Enable random number generator for platforms that support Arm
>           SMCCC TRNG interface.
>
> +config TPM_RNG
> +       bool "Enable random number generator on TPM device"
> +       depends on TPM
> +       default y
> +       help
> +         The TPM device has an inbuilt random number generator
> +         functionality. Enable random number generator on TPM
> +         devices.
> +
>  endif

We could probably skip the extra Kconfig and just look for a TPM.  But
let's leave it as is for now, it's an easy change if we ever want that

> diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
> index 2494717d7c..78f61051ac 100644
> --- a/drivers/rng/Makefile
> +++ b/drivers/rng/Makefile
> @@ -13,3 +13,4 @@ obj-$(CONFIG_RNG_STM32MP1) += stm32mp1_rng.o
>  obj-$(CONFIG_RNG_ROCKCHIP) += rockchip_rng.o
>  obj-$(CONFIG_RNG_IPROC200) += iproc_rng200.o
>  obj-$(CONFIG_RNG_SMCCC_TRNG) += smccc_trng.o
> +obj-$(CONFIG_TPM_RNG) += tpm_rng.o
> diff --git a/drivers/rng/tpm_rng.c b/drivers/rng/tpm_rng.c
> new file mode 100644
> index 0000000000..1a5e9e2e4b
> --- /dev/null
> +++ b/drivers/rng/tpm_rng.c
> @@ -0,0 +1,23 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2022, Linaro Limited
> + */
> +
> +#include <dm.h>
> +#include <rng.h>
> +#include <tpm_api.h>
> +
> +static int rng_tpm_random_read(struct udevice *dev, void *data, size_t count)
> +{
> +       return tpm_get_random(dev_get_parent(dev), data, count);
> +}
> +
> +static const struct dm_rng_ops tpm_rng_ops = {
> +       .read = rng_tpm_random_read,
> +};
> +
> +U_BOOT_DRIVER(tpm_rng) = {
> +       .name   = "tpm-rng",
> +       .id     = UCLASS_RNG,
> +       .ops    = &tpm_rng_ops,
> +};
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 7dd777b56a..e888c29245 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -360,6 +360,7 @@ source lib/crypt/Kconfig
>  config TPM
>         bool "Trusted Platform Module (TPM) Support"
>         depends on DM
> +       imply DM_RNG
>         help
>           This enables support for TPMs which can be used to provide security
>           features for your board. The TPM can be connected via LPC or I2C
> diff --git a/lib/tpm_api.c b/lib/tpm_api.c
> index 4ac4612c81..032f383ca0 100644
> --- a/lib/tpm_api.c
> +++ b/lib/tpm_api.c
> @@ -269,7 +269,7 @@ u32 tpm_get_random(struct udevice *dev, void *data, u32 count)
>         if (tpm_is_v1(dev))
>                 return tpm1_get_random(dev, data, count);
>         else if (tpm_is_v2(dev))
> -               return -ENOSYS; /* not implemented yet */
> -       else
> -               return -ENOSYS;
> +               return tpm2_get_random(dev, data, count);
> +
> +       return -ENOSYS;
>  }
> --
> 2.34.1
>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>