fbdev: make the best-fit section of fb_find_mode return the closest matching mode

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@gentoo.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 8 deletions

diff --git a/drivers/video/modedb.c b/drivers/video/modedb.c
index 08d072552233..640351c9a9e1 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);