dtrm/edid: Allow comma separated edid binaries. (v3)

Allow comma separated filenames in the edid_firmware parameter.

For example:

edid_firmware=eDP-1:edid/1280x480.bin,DP-2:edid/1920x1080.bin

v2: Use strsep() to simplify parsing of comma seperated string. (Matt)
    Move initial bail before strdup. (Matt)
v3: Changed conditionals after while loop to make more readable (Jani)
    Updated kernel-parameters.txt to reflect changes (Jani)
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Bob Paauwe <bob.j.paauwe@intel.com>
[danvet: Flatten else control flow and appease checkpatch.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Documentation/kernel-parameters.txt

@@ -927,11 +927,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			The filter can be disabled or changed to another
 			driver later using sysfs.
 
-	drm_kms_helper.edid_firmware=[<connector>:]<file>
-			Broken monitors, graphic adapters and KVMs may
-			send no or incorrect EDID data sets. This parameter
-			allows to specify an EDID data set in the
-			/lib/firmware directory that is used instead.
+	drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
+			Broken monitors, graphic adapters, KVMs and EDIDless
+			panels may send no or incorrect EDID data sets.
+			This parameter allows to specify an EDID data sets
+			in the /lib/firmware directory that are used instead.
 			Generic built-in EDID data sets are used, if one of
 			edid/1024x768.bin, edid/1280x1024.bin,
 			edid/1680x1050.bin, or edid/1920x1080.bin is given
@@ -940,7 +940,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			available in Documentation/EDID/HOWTO.txt. An EDID
 			data set will only be used for a particular connector,
 			if its name and a colon are prepended to the EDID
-			name.
+			name. Each connector may use a unique EDID data
+			set by separating the files with a comma.  An EDID
+			data set with no connector name will be used for
+			any connectors not explicitly specified.
 
 	dscc4.setup=	[NET]
 

drivers/gpu/drm/drm_edid_load.c

@@ -264,27 +264,52 @@ static void *edid_load(struct drm_connector *connector, const char *name,
 int drm_load_edid_firmware(struct drm_connector *connector)
 {
 	const char *connector_name = connector->name;
-	char *edidname = edid_firmware, *last, *colon;
+	char *edidname, *last, *colon, *fwstr, *edidstr, *fallback = NULL;
 	int ret;
 	struct edid *edid;
 
-	if (*edidname == '\0')
+	if (edid_firmware[0] == '\0')
 		return 0;
 
+	/*
+	 * If there are multiple edid files specified and separated
+	 * by commas, search through the list looking for one that
+	 * matches the connector.
+	 *
+	 * If there's one or more that don't't specify a connector, keep
+	 * the last one found one as a fallback.
+	 */
+	fwstr = kstrdup(edid_firmware, GFP_KERNEL);
+	edidstr = fwstr;
+
+	while ((edidname = strsep(&edidstr, ","))) {
 		colon = strchr(edidname, ':');
 		if (colon != NULL) {
 			if (strncmp(connector_name, edidname, colon - edidname))
-			return 0;
+				continue;
 			edidname = colon + 1;
-		if (*edidname == '\0')
+			break;
+		}
+
+		if (*edidname != '\0') /* corner case: multiple ',' */
+			fallback = edidname;
+	}
+
+	if (!edidname) {
+		if (!fallback) {
+			kfree(fwstr);
 			return 0;
 		}
+		edidname = fallback;
+	}
 
 	last = edidname + strlen(edidname) - 1;
 	if (*last == '\n')
 		*last = '\0';
 
 	edid = edid_load(connector, edidname, connector_name);
+	kfree(fwstr);
+
 	if (IS_ERR_OR_NULL(edid))
 		return 0;