[PATCH v3 1/3] hw/i2c: add smbus pec utility function

[Klaus Jensen <its@irrelevant.dk>]

From: Klaus Jensen <k.jensen@samsung.com>

Add i2c_smbus_pec() to calculate the SMBus Packet Error Code for a
message.

Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
---
 hw/i2c/smbus_master.c         | 28 ++++++++++++++++++++++++++++
 include/hw/i2c/smbus_master.h |  2 ++
 2 files changed, 30 insertions(+)

diff --git a/hw/i2c/smbus_master.c b/hw/i2c/smbus_master.c
index 6a53c34e70b7..47f9eb24e033 100644
--- a/hw/i2c/smbus_master.c
+++ b/hw/i2c/smbus_master.c
@@ -15,6 +15,34 @@
 #include "hw/i2c/i2c.h"
 #include "hw/i2c/smbus_master.h"
 
+static uint8_t crc8(uint16_t data)
+{
+#define POLY (0x1070U << 3)
+    int i;
+
+    for (i = 0; i < 8; i++) {
+        if (data & 0x8000) {
+            data = data ^ POLY;
+        }
+
+        data = data << 1;
+    }
+
+    return (uint8_t)(data >> 8);
+#undef POLY
+}
+
+uint8_t i2c_smbus_pec(uint8_t crc, uint8_t *buf, size_t len)
+{
+    int i;
+
+    for (i = 0; i < len; i++) {
+        crc = crc8((crc ^ buf[i]) << 8);
+    }
+
+    return crc;
+}
+
 /* Master device commands.  */
 int smbus_quick_command(I2CBus *bus, uint8_t addr, int read)
 {
diff --git a/include/hw/i2c/smbus_master.h b/include/hw/i2c/smbus_master.h
index bb13bc423c22..d90f81767d86 100644
--- a/include/hw/i2c/smbus_master.h
+++ b/include/hw/i2c/smbus_master.h
@@ -27,6 +27,8 @@
 
 #include "hw/i2c/i2c.h"
 
+uint8_t i2c_smbus_pec(uint8_t crc, uint8_t *buf, size_t len);
+
 /* Master device commands.  */
 int smbus_quick_command(I2CBus *bus, uint8_t addr, int read);
 int smbus_receive_byte(I2CBus *bus, uint8_t addr);
-- 
2.40.0