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

[Sughosh Ganu]

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 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)
+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;
+
+	ret = device_bind_driver(dev, drv, "tpm-rng0", &child);
+	if (ret == -ENOENT) {
+		log_err("No driver configured for tpm-rng device\n");
+		return 0;
+	}
+
+	if (ret) {
+		log_err("Unable to bind rng driver with the tpm-rng device\n");
+		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)
+	.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
 	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