Re: [PATCH v4 4/8] tpm: Add the RNG child device

Hi Sughosh,

On Wed, 9 Mar 2022 at 05:28, Sughosh Ganu sughosh.ganu@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@linaro.org

Changes since V3:

• Build the RNG child addition only for the u-boot proper stage using the CONFIG_{SPL,TPL}_BUILD guards instead of CONFIG_TPM config which gets included in all stages.
• Remove the child_pre_probe callback which was starting the TPM device based on review from Simon.

drivers/tpm/tpm-uclass.c | 40 ++++++++++++++++++++++++++++++++++++---- lib/Kconfig | 1 + 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/drivers/tpm/tpm-uclass.c b/drivers/tpm/tpm-uclass.c index f67fe1019b..241ed01e68 100644 --- a/drivers/tpm/tpm-uclass.c +++ b/drivers/tpm/tpm-uclass.c @@ -11,10 +11,16 @@ #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_RNG1_DRV_NAME "tpm1-rng" +#define TPM_RNG2_DRV_NAME "tpm2-rng"

int tpm_open(struct udevice *dev) { struct tpm_ops *ops = tpm_get_ops(dev); @@ -136,12 +142,38 @@ int tpm_xfer(struct udevice *dev, const uint8_t *sendbuf, size_t send_size, return 0; }

+#if !IS_ENABLED(CONFIG_SPL_BUILD) && !IS_ENABLED(CONFIG_TPL_BUILD)

Drop that

+static int tpm_uclass_post_probe(struct udevice *dev) +{

•   int ret;
  

•   const char *drv = tpm_is_v1(dev) ?
  

•           TPM_RNG1_DRV_NAME : TPM_RNG2_DRV_NAME;
  

•   struct udevice *child;
  

if (CONFIG_IS_ENABLED(TPM_RNG)) {

•   ret = device_bind_driver(dev, drv, "tpm-rng0", &child);
  

•   if (ret == -ENOENT) {
  

•           log_err("No driver configured for tpm-rng device\n");
  

That is a lot of code size for the string that will likely never happen. You can use

•           return 0;
  

You should report the error.

•   }
  

•   if (ret) {
  

•           log_err("Unable to bind rng driver with the tpm-rng device\n");
  

You might want to use

return log_msg_ret("bind", ret)

since it doesn't add to code since unless you turn on CONFIG_LOG_ERROR_RETURN

•           return ret;
  

•   }
  

•   return 0;
  

+} +#endif /* !CONFIG_SPL_BUILD && !CONFIG_TPL_BUILD */

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 +#if !IS_ENABLED(CONFIG_SPL_BUILD) && !IS_ENABLED(CONFIG_TPL_BUILD)

Drop that and do it in the function as above

•   .post_probe             = tpm_uclass_post_probe,
  

#endif .per_device_auto = sizeof(struct tpm_chip_priv), }; diff --git a/lib/Kconfig b/lib/Kconfig index 3c6fa99b1a..0f05c97afc 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -341,6 +341,7 @@ source lib/crypt/Kconfig config TPM bool "Trusted Platform Module (TPM) Support" depends on DM

•   select DM_RNG
  

imply might be better, so boards can disable it.

    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

-- 2.25.1

Regards, Simon