[PATCH v6 3/7] 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 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) {
+			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