n_tty: drop n_tty_receive_buf_fast

After the previous patches, n_tty_receive_buf_standard and
n_tty_receive_buf_fast differ only in handling of tty line and input
controls. Unlike n_tty_receive_buf_fast, n_tty_receive_buf_standard
handles them all (I_ISTRIP, I_IUCLC, L_IEXTEN, L_EXTPROC, and I_PARMRK).

So remove n_tty_receive_buf_fast and let n_tty_receive_buf_standard do
the handling. Actually most of the tests are only moved from
__receive_buf to n_tty_receive_buf_standard.

Again, the code duplication is not worth the theoretical speedup.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210505091928.22010-5-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

@@ -1530,9 +1530,8 @@ n_tty_receive_buf_closing(struct tty_struct *tty, const unsigned char *cp,
 	}
 }
 
-static void
-n_tty_receive_buf_standard(struct tty_struct *tty, const unsigned char *cp,
-			  char *fp, int count)
+static void n_tty_receive_buf_standard(struct tty_struct *tty,
+		const unsigned char *cp, char *fp, int count)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 	char flag = TTY_NORMAL;
@@ -1564,32 +1563,6 @@ n_tty_receive_buf_standard(struct tty_struct *tty, const unsigned char *cp,
 	}
 }
 
-static void
-n_tty_receive_buf_fast(struct tty_struct *tty, const unsigned char *cp,
-		       char *fp, int count)
-{
-	struct n_tty_data *ldata = tty->disc_data;
-	char flag = TTY_NORMAL;
-
-	while (count--) {
-		if (fp)
-			flag = *fp++;
-		if (likely(flag == TTY_NORMAL)) {
-			unsigned char c = *cp++;
-
-			if (!test_bit(c, ldata->char_map))
-				n_tty_receive_char(tty, c, false);
-			else if (n_tty_receive_char_special(tty, c) && count) {
-				if (fp)
-					flag = *fp++;
-				n_tty_receive_char_lnext(tty, *cp++, flag);
-				count--;
-			}
-		} else
-			n_tty_receive_char_flagged(tty, *cp++, flag);
-	}
-}
-
 static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
 			  char *fp, int count)
 {
@@ -1612,10 +1585,7 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
 			count--;
 		}
 
-		if (!preops && !I_PARMRK(tty))
-			n_tty_receive_buf_fast(tty, cp, fp, count);
-		else
-			n_tty_receive_buf_standard(tty, cp, fp, count);
+		n_tty_receive_buf_standard(tty, cp, fp, count);
 
 		flush_echoes(tty);
 		if (tty->ops->flush_chars)