Move rand_bytes implementation from tpm2 to chip/g.

BRANCH=none
TEST=none
BUG=chrome-os-partner:43025,chrome-os-partner:47524
Signed-off-by: nagendra modadugu <ngm@google.com>

Change-Id: Ic7a850fdf2594ac1981237edda8dceb16cc7cbe6
Reviewed-on: https://chromium-review.googlesource.com/319155
Commit-Ready: Nagendra Modadugu <ngm@google.com>
Tested-by: Nagendra Modadugu <ngm@google.com>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

3 files changed, 35 insertions, 21 deletions

diff --git a/board/cr50/tpm2/platform.c b/board/cr50/tpm2/platform.c
index afe5c86c74..20b5854625 100644
--- a/board/cr50/tpm2/platform.c
+++ b/board/cr50/tpm2/platform.c
@@ -8,26 +8,9 @@
 
 #include "trng.h"
 
-UINT16 _cpri__GenerateRandom(INT32 randomSize,
-			     BYTE *buffer)
+uint16_t _cpri__GenerateRandom(size_t random_size,
+			uint8_t *buffer)
 {
-	int random_togo = 0;
-	int buffer_index = 0;
-	uint32_t random_value;
-
-	/*
-	 * Retrieve random numbers in 4 byte quantities and pack as many bytes
-	 * as needed into 'buffer'. If randomSize is not divisible by 4, the
-	 * remaining random bytes get dropped.
-	 */
-	while (buffer_index < randomSize) {
-		if (!random_togo) {
-			random_value = rand();
-			random_togo = sizeof(random_value);
-		}
-		buffer[buffer_index++] = random_value >>
-			((random_togo-- - 1) * 8);
-	}
-
-	return randomSize;
+	rand_bytes(buffer, random_size);
+	return random_size;
 }
diff --git a/chip/g/trng.c b/chip/g/trng.c
index e462127da8..b6a062d58d 100644
--- a/chip/g/trng.c
+++ b/chip/g/trng.c
@@ -20,3 +20,25 @@ uint32_t rand(void)
 		;
 	return GREAD(TRNG, READ_DATA);
 }
+
+void rand_bytes(void *buffer, size_t len)
+{
+	int random_togo = 0;
+	int buffer_index = 0;
+	uint32_t random_value;
+	uint8_t *buf = (uint8_t *) buffer;
+
+	/*
+	 * Retrieve random numbers in 4 byte quantities and pack as many bytes
+	 * as needed into 'buffer'. If len is not divisible by 4, the
+	 * remaining random bytes get dropped.
+	 */
+	while (buffer_index < len) {
+		if (!random_togo) {
+			random_value = rand();
+			random_togo = sizeof(random_value);
+		}
+		buf[buffer_index++] = random_value >>
+			((random_togo-- - 1) * 8);
+	}
+}
diff --git a/include/trng.h b/include/trng.h
index fe1c96825e..a35496c3fd 100644
--- a/include/trng.h
+++ b/include/trng.h
@@ -5,6 +5,8 @@
 #ifndef __EC_INCLUDE_TRNG_H
 #define __EC_INCLUDE_TRNG_H
 
+#include <sys/types.h>
+
 /**
  * Initialize the true random number generator.
  *
@@ -19,4 +21,11 @@ void init_trng(void);
  **/
 uint32_t rand(void);
 
+/**
+ * Output len random bytes into buffer.
+ *
+ * Not supported on all platforms.
+ **/
+void rand_bytes(void *buffer, size_t len);
+
 #endif /* __EC_INCLUDE_TRNG_H */