Merge "Add fast, inexpensive static CRC scheme" into android-msm-eos-5.4

1 files changed, 45 insertions, 14 deletions

diff --git a/comms.c b/comms.c
index 480ebea..691efee 100644
--- a/comms.c
+++ b/comms.c
@@ -33,6 +33,15 @@
 #define BUSY_DELAY_MAX_US       100000
 #define BUSY_BACKOFF_RATE       2
 
+// CRC Schemes:
+//  CRC_CRC32 Expensive on CPU, battery and bandwidth, catches random bit flips.
+//            Good for hw validation, but not production.
+//  CRC_STATIC Fast, inexpensive, catches protocol errors but not bit flips.
+
+#define CRC_CRC32
+#undef  CRC_STATIC
+#define CRC_STATIC_VALUE        0x5A5A5A5A
+
 static const uint32_t crc_table[] = {
 	0x00000000, 0x04C11DB7, 0x09823B6E, 0x0D4326D9,
 	0x130476DC, 0x17C56B6B, 0x1A864DB2, 0x1E475005,
@@ -71,6 +80,40 @@ uint32_t crc32(const uint8_t *buffer, int length, uint32_t crc)
 	return crc;
 }
 
+void crc_create(struct nanohub_packet *packet)
+{
+	struct nanohub_packet_crc crc;
+#if defined(CRC_CRC32)
+	crc.crc = crc32((uint8_t *)packet,
+			sizeof(struct nanohub_packet) + packet->len, ~0);
+#elif defined(CRC_STATIC)
+	crc.crc = CRC_STATIC_VALUE;
+#endif
+	memcpy(&packet->data[packet->len], &crc.crc,
+	       sizeof(struct nanohub_packet_crc));
+}
+
+int crc_verify(struct nanohub_packet *packet)
+{
+	struct nanohub_packet_crc crc;
+	int cmp;
+
+	// first check static crc
+	crc.crc = CRC_STATIC_VALUE;
+	cmp = memcmp(&crc.crc, &packet->data[packet->len],
+		     sizeof(struct nanohub_packet_crc));
+	if (cmp == 0)
+		return 0;
+
+	// check computed crc
+	crc.crc = crc32((uint8_t *)packet,
+			sizeof(struct nanohub_packet) + packet->len, ~0);
+	cmp = memcmp(&crc.crc, &packet->data[packet->len],
+		     sizeof(struct nanohub_packet_crc));
+
+	return cmp;
+}
+
 static inline size_t pad(size_t length)
 {
 	return (length + 3) & ~3;
@@ -96,7 +139,6 @@ static int packet_create(struct nanohub_packet *packet, uint32_t seq,
 			 uint32_t reason, uint8_t id, uint8_t len,
 			 const uint8_t *data, bool user)
 {
-	struct nanohub_packet_crc crc;
 	int ret = sizeof(struct nanohub_packet) + len +
 	    sizeof(struct nanohub_packet_crc);
 
@@ -115,11 +157,7 @@ static int packet_create(struct nanohub_packet *packet, uint32_t seq,
 				memcpy(packet->data, data, len);
 			}
 		}
-		crc.crc =
-		    crc32((uint8_t *) packet,
-			  sizeof(struct nanohub_packet) + len, ~0);
-		memcpy(&packet->data[len], &crc.crc,
-		       sizeof(struct nanohub_packet_crc));
+		crc_create(packet);
 	} else {
 		ret = ERROR_NACK;
 	}
@@ -132,14 +170,7 @@ static int packet_verify(struct nanohub_packet *packet)
 	struct nanohub_packet_crc crc;
 	int cmp;
 
-	crc.crc =
-	    crc32((uint8_t *) packet,
-		  sizeof(struct nanohub_packet) + packet->len, ~0);
-
-	cmp =
-	    memcmp(&crc.crc, &packet->data[packet->len],
-		   sizeof(struct nanohub_packet_crc));
-
+	cmp = crc_verify(packet);
 	if (cmp != 0) {
 		uint8_t *ptr = (uint8_t *)packet;
 		pr_debug("nanohub: gen crc: %08x, got crc: %08x\n", crc.crc,