[PATCH v6 3/7] tpm: Add the RNG child device

[Simon Glass]

Hi Sughosh,

On Mon, 4 Jul 2022 at 07:35, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
>
> The TPM device comes with the random number generator(RNG)
> functionality which is built into the TPM device. Add logic to add the
> RNG child device in the TPM uclass post probe callback.
>
> The RNG device can then be used to pass a set of random bytes to the
> linux kernel, need for address space randomisation through the
> EFI_RNG_PROTOCOL interface.
>
> Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> ---
> Changes since V5:
> * Check if the TPM RNG device has already been added, through a call
>   to device_find_first_child_by_uclass()
>
>  drivers/tpm/tpm-uclass.c | 37 +++++++++++++++++++++++++++++++++----
>  1 file changed, 33 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tpm/tpm-uclass.c b/drivers/tpm/tpm-uclass.c
> index f67fe1019b..e1f1ef01e1 100644
> --- a/drivers/tpm/tpm-uclass.c
> +++ b/drivers/tpm/tpm-uclass.c
> @@ -11,10 +11,15 @@
>  #include <log.h>
>  #include <linux/delay.h>
>  #include <linux/unaligned/be_byteshift.h>
> +#include <tpm_api.h>
>  #include <tpm-v1.h>
>  #include <tpm-v2.h>
>  #include "tpm_internal.h"
>
> +#include <dm/lists.h>
> +
> +#define TPM_RNG_DRV_NAME       "tpm-rng"
> +
>  int tpm_open(struct udevice *dev)
>  {
>         struct tpm_ops *ops = tpm_get_ops(dev);
> @@ -136,12 +141,36 @@ int tpm_xfer(struct udevice *dev, const uint8_t *sendbuf, size_t send_size,
>         return 0;
>  }
>
> +static int tpm_uclass_post_probe(struct udevice *dev)
> +{
> +       int ret;
> +       const char *drv = TPM_RNG_DRV_NAME;
> +       struct udevice *child;
> +
> +       if (CONFIG_IS_ENABLED(TPM_RNG)) {
> +               ret = device_find_first_child_by_uclass(dev, UCLASS_RNG,
> +                                                       &child);
> +
> +               if (ret != -ENODEV) {

This may return -EIO (for example) in which case your log message is incorrect.


> +                       log_debug("RNG child already added to the TPM device\n");
> +                       return ret;
> +               }
> +
> +               ret = device_bind_driver(dev, drv, "tpm-rng0", &child);
> +               if (ret)
> +                       return log_msg_ret("bind", ret);
> +       }
> +
> +       return 0;
> +}
> +
>  UCLASS_DRIVER(tpm) = {
> -       .id             = UCLASS_TPM,
> -       .name           = "tpm",
> -       .flags          = DM_UC_FLAG_SEQ_ALIAS,
> +       .id                     = UCLASS_TPM,
> +       .name                   = "tpm",
> +       .flags                  = DM_UC_FLAG_SEQ_ALIAS,
>  #if CONFIG_IS_ENABLED(OF_REAL)
> -       .post_bind      = dm_scan_fdt_dev,
> +       .post_bind              = dm_scan_fdt_dev,
>  #endif
> +       .post_probe             = tpm_uclass_post_probe,
>         .per_device_auto        = sizeof(struct tpm_chip_priv),
>  };
> --
> 2.25.1
>

The driver needs a compatible string so it can be in the device tree.

Regards,
Simon