[PATCH v2 3/6] tty: n_gsm: replace use of gsm_read_ea() with gsm_read_ea_val()

["D. Starke" <daniel.starke@siemens.com>]

From: Daniel Starke <daniel.starke@siemens.com>

Replace the use of gsm_read_ea() with gsm_read_ea_val() where applicable to
improve code readability and avoid errors like in the past.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
---
 drivers/tty/n_gsm.c | 99 +++++++++++++++++++++++----------------------
 1 file changed, 51 insertions(+), 48 deletions(-)

Changes since v1:
Fixed use of wrong variable in debug output within gsm_dlci_data().

Link: https://lore.kernel.org/all/202208222147.WfFRmf1r-lkp@intel.com/

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index ed399d57b197..9535e84f3063 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1418,18 +1418,13 @@ static void gsm_control_modem(struct gsm_mux *gsm, const u8 *data, int clen)
 	unsigned int modem = 0;
 	struct gsm_dlci *dlci;
 	int len = clen;
-	int slen;
+	int cl = clen;
 	const u8 *dp = data;
 	struct tty_struct *tty;
 
-	while (gsm_read_ea(&addr, *dp++) == 0) {
-		len--;
-		if (len == 0)
-			return;
-	}
-	/* Must be at least one byte following the EA */
-	len--;
-	if (len <= 0)
+	len = gsm_read_ea_val(&addr, data, cl);
+
+	if (len < 1)
 		return;
 
 	addr >>= 1;
@@ -1438,15 +1433,21 @@ static void gsm_control_modem(struct gsm_mux *gsm, const u8 *data, int clen)
 		return;
 	dlci = gsm->dlci[addr];
 
-	slen = len;
-	while (gsm_read_ea(&modem, *dp++) == 0) {
-		len--;
-		if (len == 0)
-			return;
-	}
-	len--;
+	/* Must be at least one byte following the EA */
+	if ((cl - len) < 1)
+		return;
+
+	dp += len;
+	cl -= len;
+
+	/* get the modem status */
+	len = gsm_read_ea_val(&modem, dp, cl);
+
+	if (len < 1)
+		return;
+
 	tty = tty_port_tty_get(&dlci->port);
-	gsm_process_modem(tty, dlci, modem, slen - len);
+	gsm_process_modem(tty, dlci, modem, cl);
 	if (tty) {
 		tty_wakeup(tty);
 		tty_kref_put(tty);
@@ -1921,11 +1922,10 @@ static void gsm_dlci_data(struct gsm_dlci *dlci, const u8 *data, int clen)
 	struct tty_port *port = &dlci->port;
 	struct tty_struct *tty;
 	unsigned int modem = 0;
-	int len = clen;
-	int slen = 0;
+	int len;
 
 	if (debug & 16)
-		pr_debug("%d bytes for tty\n", len);
+		pr_debug("%d bytes for tty\n", clen);
 	switch (dlci->adaption)  {
 	/* Unsupported types */
 	case 4:		/* Packetised interruptible data */
@@ -1933,24 +1933,22 @@ static void gsm_dlci_data(struct gsm_dlci *dlci, const u8 *data, int clen)
 	case 3:		/* Packetised uininterruptible voice/data */
 		break;
 	case 2:		/* Asynchronous serial with line state in each frame */
-		while (gsm_read_ea(&modem, *data++) == 0) {
-			len--;
-			slen++;
-			if (len == 0)
-				return;
-		}
-		len--;
-		slen++;
+		len = gsm_read_ea_val(&modem, data, clen);
+		if (len < 1)
+			return;
 		tty = tty_port_tty_get(port);
 		if (tty) {
-			gsm_process_modem(tty, dlci, modem, slen);
+			gsm_process_modem(tty, dlci, modem, len);
 			tty_wakeup(tty);
 			tty_kref_put(tty);
 		}
+		/* Skip processed modem data */
+		data += len;
+		clen -= len;
 		fallthrough;
 	case 1:		/* Line state will go via DLCI 0 controls only */
 	default:
-		tty_insert_flip_string(port, data, len);
+		tty_insert_flip_string(port, data, clen);
 		tty_flip_buffer_push(port);
 	}
 }
@@ -1971,24 +1969,29 @@ static void gsm_dlci_command(struct gsm_dlci *dlci, const u8 *data, int len)
 {
 	/* See what command is involved */
 	unsigned int command = 0;
-	while (len-- > 0) {
-		if (gsm_read_ea(&command, *data++) == 1) {
-			int clen = *data++;
-			len--;
-			/* FIXME: this is properly an EA */
-			clen >>= 1;
-			/* Malformed command ? */
-			if (clen > len)
-				return;
-			if (command & 1)
-				gsm_control_message(dlci->gsm, command,
-								data, clen);
-			else
-				gsm_control_response(dlci->gsm, command,
-								data, clen);
-			return;
-		}
-	}
+	const u8 *dp = data;
+	int clen = 0;
+	int dlen;
+
+	/* read the command */
+	dlen = gsm_read_ea_val(&command, dp, len);
+	len -= dlen;
+	dp += dlen;
+
+	/* read any control data */
+	dlen = gsm_read_ea_val(&clen, dp, len);
+	len -= dlen;
+	dp += dlen;
+
+	/* Malformed command? */
+	if (clen > len)
+		return;
+
+	if (command & 1)
+		gsm_control_message(dlci->gsm, command, dp, clen);
+	else
+		gsm_control_response(dlci->gsm, command, dp, clen);
+	return;
 }
 
 /**
-- 
2.34.1