serial: earlycon: prefer EARLYCON_DECLARE() variant

If a driver exposes early consoles with EARLYCON_DECLARE() and
OF_EARLYCON_DECLARE(), pefer the non-OF variant if the user specifies it
by
  earlycon=<driver>,<options>

The rationale behind this is that some drivers register multiple setup
functions under the same driver name. Eg.

OF_EARLYCON_DECLARE(lpuart, "fsl,vf610-lpuart", lpuart_early_console_setup);
OF_EARLYCON_DECLARE(lpuart32, "fsl,ls1021a-lpuart", lpuart32_early_console_setup);
OF_EARLYCON_DECLARE(lpuart32, "fsl,imx7ulp-lpuart", lpuart32_imx_early_console_setup);
EARLYCON_DECLARE(lpuart, lpuart_early_console_setup);
EARLYCON_DECLARE(lpuart32, lpuart32_early_console_setup);

It depends on the order of the entries which console_setup() actually
gets called. To make things worse, I guess it also depends on the
compiler how these are ordered. Thus always prefer the EARLYCON_DECLARE()
ones.
Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20200220174607.24285-1-michael@walle.ccSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/earlycon.c

@@ -170,6 +170,7 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
 int __init setup_earlycon(char *buf)
 {
 	const struct earlycon_id **p_match;
+	bool empty_compatible = true;
 
 	if (!buf || !buf[0])
 		return -EINVAL;
@@ -177,6 +178,7 @@ int __init setup_earlycon(char *buf)
 	if (early_con.flags & CON_ENABLED)
 		return -EALREADY;
 
+again:
 	for (p_match = __earlycon_table; p_match < __earlycon_table_end;
 	     p_match++) {
 		const struct earlycon_id *match = *p_match;
@@ -185,6 +187,10 @@ int __init setup_earlycon(char *buf)
 		if (strncmp(buf, match->name, len))
 			continue;
 
+		/* prefer entries with empty compatible */
+		if (empty_compatible && *match->compatible)
+			continue;
+
 		if (buf[len]) {
 			if (buf[len] != ',')
 				continue;
@@ -195,6 +201,11 @@ int __init setup_earlycon(char *buf)
 		return register_earlycon(buf, match);
 	}
 
+	if (empty_compatible) {
+		empty_compatible = false;
+		goto again;
+	}
+
 	return -ENOENT;
 }