drm/modes: Move named modes parsing to a separate function

The current construction of the named mode parsing doesn't allow to extend
it easily. Let's move it to a separate function so we can add more
parameters and modes.

In order for the tests to still pass, some extra checks are needed, so
it's not a 1:1 move.
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v9-9-24b168e5bcd5@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/drm_modes.c

@@ -1755,6 +1755,51 @@ static const char * const drm_named_modes_whitelist[] = {
 	"PAL",
 };
 
+static int drm_mode_parse_cmdline_named_mode(const char *name,
+					     unsigned int name_end,
+					     struct drm_cmdline_mode *cmdline_mode)
+{
+	unsigned int i;
+
+	if (!name_end)
+		return 0;
+
+	/* If the name starts with a digit, it's not a named mode */
+	if (isdigit(name[0]))
+		return 0;
+
+	/*
+	 * If there's an equal sign in the name, the command-line
+	 * contains only an option and no mode.
+	 */
+	if (strnchr(name, name_end, '='))
+		return 0;
+
+	/* The connection status extras can be set without a mode. */
+	if (name_end == 1 &&
+	    (name[0] == 'd' || name[0] == 'D' || name[0] == 'e'))
+		return 0;
+
+	/*
+	 * We're sure we're a named mode at this point, iterate over the
+	 * list of modes we're aware of.
+	 */
+	for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
+		int ret;
+
+		ret = str_has_prefix(name, drm_named_modes_whitelist[i]);
+		if (ret != name_end)
+			continue;
+
+		strcpy(cmdline_mode->name, drm_named_modes_whitelist[i]);
+		cmdline_mode->specified = true;
+
+		return 1;
+	}
+
+	return -EINVAL;
+}
+
 /**
  * drm_mode_parse_command_line_for_connector - parse command line modeline for connector
  * @mode_option: optional per connector mode option
@@ -1791,7 +1836,7 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
 	const char *bpp_ptr = NULL, *refresh_ptr = NULL, *extra_ptr = NULL;
 	const char *options_ptr = NULL;
 	char *bpp_end_ptr = NULL, *refresh_end_ptr = NULL;
-	int i, len, ret;
+	int len, ret;
 
 	memset(mode, 0, sizeof(*mode));
 	mode->panel_orientation = DRM_MODE_PANEL_ORIENTATION_UNKNOWN;
@@ -1832,18 +1877,19 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
 		parse_extras = true;
 	}
 
-	/* First check for a named mode */
-	for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
-		ret = str_has_prefix(name, drm_named_modes_whitelist[i]);
-		if (ret == mode_end) {
-			if (refresh_ptr)
-				return false; /* named + refresh is invalid */
+	if (!mode_end)
+		return false;
 
-			strcpy(mode->name, drm_named_modes_whitelist[i]);
-			mode->specified = true;
-			break;
-		}
-	}
+	ret = drm_mode_parse_cmdline_named_mode(name, mode_end, mode);
+	if (ret < 0)
+		return false;
+
+	/*
+	 * Having a mode that starts by a letter (and thus is named) and
+	 * an at-sign (used to specify a refresh rate) is disallowed.
+	 */
+	if (ret && refresh_ptr)
+		return false;
 
 	/* No named mode? Check for a normal mode argument, e.g. 1024x768 */
 	if (!mode->specified && isdigit(name[0])) {