[PATCH] fbdev: find mode with the highest/safest refresh rate in fb_find_mode()

[Michal Januszewski <spock@gentoo.org>]

Currently, if the refresh rate is not specified, fb_find_mode() returns
the first known video mode with the requested resolution, which provides
no guarantees wrt the refresh rate.  Change this so that the mode with
the highest refresh rate is returned when the driver provides a custom
video mode database and the monitor limits, and a mode with the safe
60 Hz refresh rate otherwise.

Signed-off-by: Michal Januszewski <spock@gentoo.org>
---
diff --git a/drivers/video/modedb.c b/drivers/video/modedb.c
index 3741ad7..9598c46 100644
--- a/drivers/video/modedb.c
+++ b/drivers/video/modedb.c
@@ -606,26 +606,43 @@ done:
 	DPRINTK("Trying specified video mode%s %ix%i\n",
 	    refresh_specified ? "" : " (ignoring refresh rate)", xres, yres);
 
-	diff = refresh;
+	if (!refresh_specified) {
+		/*
+		 * If the caller has provided a custom mode database and a
+		 * valid monspecs structure, we look for the mode with the
+		 * highest refresh rate.  Otherwise we play it safe it and
+		 * try to find a mode with a refresh rate closest to the
+		 * standard 60 Hz.
+		 */
+		if (db != modedb &&
+		    info->monspecs.vfmin && info->monspecs.vfmax &&
+		    info->monspecs.hfmin && info->monspecs.hfmax &&
+		    info->monspecs.dclkmax) {
+			refresh = 1000;
+		} else {
+			refresh = 60;
+		}
+	}
+
+	diff = -1;
 	best = -1;
 	for (i = 0; i < dbsize; i++) {
-		if (name_matches(db[i], name, namelen) ||
-		    (res_specified && res_matches(db[i], xres, yres))) {
-			if(!fb_try_mode(var, info, &db[i], bpp)) {
-				if(!refresh_specified || db[i].refresh == refresh)
-					return 1;
-				else {
-					if(diff > abs(db[i].refresh - refresh)) {
-						diff = abs(db[i].refresh - refresh);
-						best = i;
-					}
+		if ((name_matches(db[i], name, namelen) ||
+		    (res_specified && res_matches(db[i], xres, yres))) &&
+		    !fb_try_mode(var, info, &db[i], bpp)) {
+			if (refresh_specified && db[i].refresh == refresh) {
+				return 1;
+			} else {
+				if (abs(db[i].refresh - refresh) < diff) {
+					diff = abs(db[i].refresh - refresh);
+					best = i;
 				}
 			}
 		}
 	}
 	if (best != -1) {
 		fb_try_mode(var, info, &db[best], bpp);
-		return 2;
+		return (refresh_specified) ? 2 : 1;
 	}
 
 	diff = xres + yres;


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