import diagchar.[ch] from linux kernel of Quectel EC25 module
Rather than running our own, we should just use the same HDLC code that
Qualcomm also uses. It's GPLv2 from the Qualcomm Linux kerenl sources.
diff --git a/src/diagchar_hdlc.c b/src/diagchar_hdlc.c
new file mode 100644
index 0000000..d265746
--- /dev/null
+++ b/src/diagchar_hdlc.c
@@ -0,0 +1,267 @@
+/* Copyright (c) 2008-2009, 2012-2014, The Linux Foundation.
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/cdev.h>
+#include <linux/fs.h>
+#include <linux/device.h>
+#include <linux/uaccess.h>
+#include <linux/ratelimit.h>
+#include <linux/crc-ccitt.h>
+#include "diagchar_hdlc.h"
+#include "diagchar.h"
+
+
+MODULE_LICENSE("GPL v2");
+
+#define CRC_16_L_SEED 0xFFFF
+
+#define CRC_16_L_STEP(xx_crc, xx_c) \
+ crc_ccitt_byte(xx_crc, xx_c)
+
+void diag_hdlc_encode(struct diag_send_desc_type *src_desc,
+ struct diag_hdlc_dest_type *enc)
+{
+ uint8_t *dest;
+ uint8_t *dest_last;
+ const uint8_t *src;
+ const uint8_t *src_last;
+ uint16_t crc;
+ unsigned char src_byte = 0;
+ enum diag_send_state_enum_type state;
+ unsigned int used = 0;
+
+ if (src_desc && enc) {
+
+ /* Copy parts to local variables. */
+ src = src_desc->pkt;
+ src_last = src_desc->last;
+ state = src_desc->state;
+ dest = enc->dest;
+ dest_last = enc->dest_last;
+
+ if (state == DIAG_STATE_START) {
+ crc = CRC_16_L_SEED;
+ state++;
+ } else {
+ /* Get a local copy of the CRC */
+ crc = enc->crc;
+ }
+
+ /* dest or dest_last may be NULL to trigger a
+ state transition only */
+ if (dest && dest_last) {
+ /* This condition needs to include the possibility
+ of 2 dest bytes for an escaped byte */
+ while (src <= src_last && dest <= dest_last) {
+
+ src_byte = *src++;
+
+ if ((src_byte == CONTROL_CHAR) ||
+ (src_byte == ESC_CHAR)) {
+
+ /* If the escape character is not the
+ last byte */
+ if (dest != dest_last) {
+ crc = CRC_16_L_STEP(crc,
+ src_byte);
+
+ *dest++ = ESC_CHAR;
+ used++;
+
+ *dest++ = src_byte
+ ^ ESC_MASK;
+ used++;
+ } else {
+
+ src--;
+ break;
+ }
+
+ } else {
+ crc = CRC_16_L_STEP(crc, src_byte);
+ *dest++ = src_byte;
+ used++;
+ }
+ }
+
+ if (src > src_last) {
+
+ if (state == DIAG_STATE_BUSY) {
+ if (src_desc->terminate) {
+ crc = ~crc;
+ state++;
+ } else {
+ /* Done with fragment */
+ state = DIAG_STATE_COMPLETE;
+ }
+ }
+
+ while (dest <= dest_last &&
+ state >= DIAG_STATE_CRC1 &&
+ state < DIAG_STATE_TERM) {
+ /* Encode a byte of the CRC next */
+ src_byte = crc & 0xFF;
+
+ if ((src_byte == CONTROL_CHAR)
+ || (src_byte == ESC_CHAR)) {
+
+ if (dest != dest_last) {
+
+ *dest++ = ESC_CHAR;
+ used++;
+ *dest++ = src_byte ^
+ ESC_MASK;
+ used++;
+
+ crc >>= 8;
+ } else {
+
+ break;
+ }
+ } else {
+
+ crc >>= 8;
+ *dest++ = src_byte;
+ used++;
+ }
+
+ state++;
+ }
+
+ if (state == DIAG_STATE_TERM) {
+ if (dest_last >= dest) {
+ *dest++ = CONTROL_CHAR;
+ used++;
+ state++; /* Complete */
+ }
+ }
+ }
+ }
+ /* Copy local variables back into the encode structure. */
+
+ enc->dest = dest;
+ enc->dest_last = dest_last;
+ enc->crc = crc;
+ src_desc->pkt = src;
+ src_desc->last = src_last;
+ src_desc->state = state;
+ }
+
+ return;
+}
+
+
+int diag_hdlc_decode(struct diag_hdlc_decode_type *hdlc)
+{
+ uint8_t *src_ptr = NULL, *dest_ptr = NULL;
+ unsigned int src_length = 0, dest_length = 0;
+
+ unsigned int len = 0;
+ unsigned int i;
+ uint8_t src_byte;
+
+ int pkt_bnd = HDLC_INCOMPLETE;
+ int msg_start;
+
+ if (hdlc && hdlc->src_ptr && hdlc->dest_ptr &&
+ (hdlc->src_size > hdlc->src_idx) &&
+ (hdlc->dest_size > hdlc->dest_idx)) {
+
+ msg_start = (hdlc->src_idx == 0) ? 1 : 0;
+
+ src_ptr = hdlc->src_ptr;
+ src_ptr = &src_ptr[hdlc->src_idx];
+ src_length = hdlc->src_size - hdlc->src_idx;
+
+ dest_ptr = hdlc->dest_ptr;
+ dest_ptr = &dest_ptr[hdlc->dest_idx];
+ dest_length = hdlc->dest_size - hdlc->dest_idx;
+
+ for (i = 0; i < src_length; i++) {
+
+ src_byte = src_ptr[i];
+
+ if (hdlc->escaping) {
+ dest_ptr[len++] = src_byte ^ ESC_MASK;
+ hdlc->escaping = 0;
+ } else if (src_byte == ESC_CHAR) {
+ if (i == (src_length - 1)) {
+ hdlc->escaping = 1;
+ i++;
+ break;
+ } else {
+ dest_ptr[len++] = src_ptr[++i]
+ ^ ESC_MASK;
+ }
+ } else if (src_byte == CONTROL_CHAR) {
+ if (msg_start && i == 0 && src_length > 1)
+ continue;
+ /* Byte 0x7E will be considered
+ as end of packet */
+ dest_ptr[len++] = src_byte;
+ i++;
+ pkt_bnd = HDLC_COMPLETE;
+ break;
+ } else {
+ dest_ptr[len++] = src_byte;
+ }
+
+ if (len >= dest_length) {
+ i++;
+ break;
+ }
+ }
+
+ hdlc->src_idx += i;
+ hdlc->dest_idx += len;
+ }
+
+ return pkt_bnd;
+}
+
+int crc_check(uint8_t *buf, uint16_t len)
+{
+ uint16_t crc = CRC_16_L_SEED;
+ uint8_t sent_crc[2] = {0, 0};
+
+ /*
+ * The minimum length of a valid incoming packet is 4. 1 byte
+ * of data and 3 bytes for CRC
+ */
+ if (!buf || len < 4) {
+ pr_err_ratelimited("diag: In %s, invalid packet or length, buf: 0x%p, len: %d",
+ __func__, buf, len);
+ return -EIO;
+ }
+
+ /*
+ * Run CRC check for the original input. Skip the last 3 CRC
+ * bytes
+ */
+ crc = crc_ccitt(crc, buf, len-3);
+ crc ^= CRC_16_L_SEED;
+
+ /* Check the computed CRC against the original CRC bytes. */
+ sent_crc[0] = buf[len-3];
+ sent_crc[1] = buf[len-2];
+ if (crc != *((uint16_t *)sent_crc)) {
+ pr_debug("diag: In %s, crc mismatch. expected: %x, sent %x.\n",
+ __func__, crc, *((uint16_t *)sent_crc));
+ return -EIO;
+ }
+
+ return 0;
+}