tty: n_gsm: Fix packet data hex dump output

The module param debug for n_gsm uses KERN_INFO level, but the hexdump
now uses KERN_DEBUG level. This started after commit 091cb099
("lib/hexdump: make print_hex_dump_bytes() a nop on !DEBUG builds").
We now use dynamic_hex_dump() unless DEBUG is set.

This causes no packets to be seen with modprobe n_gsm debug=0x1f unlike
earlier. Let's fix this by adding gsm_hex_dump_bytes() that calls
print_hex_dump() with KERN_INFO to match what n_gsm is doing with the
other debug related output.

Fixes: 091cb099 ("lib/hexdump: make print_hex_dump_bytes() a nop on !DEBUG builds")
Cc: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20220512131506.1216-1-tony@atomide.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_gsm.c

@@ -444,6 +444,25 @@ static u8 gsm_encode_modem(const struct gsm_dlci *dlci)
 	return modembits;
 }
 
+static void gsm_hex_dump_bytes(const char *fname, const u8 *data,
+			       unsigned long len)
+{
+	char *prefix;
+
+	if (!fname) {
+		print_hex_dump(KERN_INFO, "", DUMP_PREFIX_NONE, 16, 1, data, len,
+			       true);
+		return;
+	}
+
+	prefix = kasprintf(GFP_KERNEL, "%s: ", fname);
+	if (!prefix)
+		return;
+	print_hex_dump(KERN_INFO, prefix, DUMP_PREFIX_OFFSET, 16, 1, data, len,
+		       true);
+	kfree(prefix);
+}
+
 /**
  *	gsm_print_packet	-	display a frame for debug
  *	@hdr: header to print before decode
@@ -508,7 +527,7 @@ static void gsm_print_packet(const char *hdr, int addr, int cr,
 	else
 		pr_cont("(F)");
 
-	print_hex_dump_bytes("", DUMP_PREFIX_NONE, data, dlen);
+	gsm_hex_dump_bytes(NULL, data, dlen);
 }
 
 
@@ -698,9 +717,7 @@ static void gsm_data_kick(struct gsm_mux *gsm, struct gsm_dlci *dlci)
 		}
 
 		if (debug & 4)
-			print_hex_dump_bytes("gsm_data_kick: ",
-					     DUMP_PREFIX_OFFSET,
-					     gsm->txframe, len);
+			gsm_hex_dump_bytes(__func__, gsm->txframe, len);
 		if (gsmld_output(gsm, gsm->txframe, len) <= 0)
 			break;
 		/* FIXME: Can eliminate one SOF in many more cases */
@@ -2444,8 +2461,7 @@ static int gsmld_output(struct gsm_mux *gsm, u8 *data, int len)
 		return -ENOSPC;
 	}
 	if (debug & 4)
-		print_hex_dump_bytes("gsmld_output: ", DUMP_PREFIX_OFFSET,
-				     data, len);
+		gsm_hex_dump_bytes(__func__, data, len);
 	return gsm->tty->ops->write(gsm->tty, data, len);
 }
 
@@ -2521,8 +2537,7 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 	char flags = TTY_NORMAL;
 
 	if (debug & 4)
-		print_hex_dump_bytes("gsmld_receive: ", DUMP_PREFIX_OFFSET,
-				     cp, count);
+		gsm_hex_dump_bytes(__func__, cp, count);
 
 	for (; count; count--, cp++) {
 		if (fp)