linux-kernel - [PATCH] fbdev: make the best-fit section of fb_find

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Date:	Sun, 10 Feb 2008 19:46:13 +0100
From:	Michal Januszewski <spock@...too.org>
To:	Krzysztof Helt <krzysztof.h1@...zta.fm>
Cc:	linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: [PATCH] fbdev: make the best-fit section of fb_find_mode return
	the closest matching mode

From: Michal Januszewski <spock@...too.org>

Currently, if a perfect match in terms of resolution is not found,
fb_find_mode() only looks for a best-fit mode among modes with a
higher resolution than the one requested.  Thus, if the user
requests a resolution higher than the largest supported one, they
are dropped to the default mode (usually a low resolution one).

Change this behaviour so that all valid video modes are considered
when looking for a best-fit mode, while still preferring modes
with a higher resolution.

Signed-off-by: Michal Januszewski <spock@...too.org>
---
diff --git a/drivers/video/modedb.c b/drivers/video/modedb.c
index 08d0725..0b6a45f 100644
--- a/drivers/video/modedb.c
+++ b/drivers/video/modedb.c
@@ -522,7 +522,7 @@ int fb_find_mode(struct fb_var_screeninfo *var,
 	int res_specified = 0, bpp_specified = 0, refresh_specified = 0;
 	unsigned int xres = 0, yres = 0, bpp = default_bpp, refresh = 0;
 	int yres_specified = 0, cvt = 0, rb = 0, interlace = 0, margins = 0;
-	u32 best, diff;
+	u32 best, diff, tdiff;
 
 	for (i = namelen-1; i >= 0; i--) {
 	    switch (name[i]) {
@@ -651,19 +651,27 @@ done:
 		return (refresh_specified) ? 2 : 1;
 	}
 
-	diff = xres + yres;
+	diff = 2 * (xres + yres);
 	best = -1;
 	DPRINTK("Trying best-fit modes\n");
 	for (i = 0; i < dbsize; i++) {
-	    if (xres <= db[i].xres && yres <= db[i].yres) {
 		DPRINTK("Trying %ix%i\n", db[i].xres, db[i].yres);
 		if (!fb_try_mode(var, info, &db[i], bpp)) {
-		    if (diff > (db[i].xres - xres) + (db[i].yres - yres)) {
-			diff = (db[i].xres - xres) + (db[i].yres - yres);
-			best = i;
-		    }
+			tdiff = abs(db[i].xres - xres) +
+				abs(db[i].yres - yres);
+
+			/*
+			 * Penalize modes with resolutions smaller
+			 * than requested.
+			 */
+			if (xres > db[i].xres || yres > db[i].yres)
+				tdiff += xres + yres;
+
+			if (diff > tdiff) {
+				diff = tdiff;
+				best = i;
+			}
 		}
-	    }
 	}
 	if (best != -1) {
 	    fb_try_mode(var, info, &db[best], bpp);
--
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