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Subject[PATCH] fbdev: make the best-fit section of fb_find_mode return the closest matching mode
From: Michal Januszewski <spock@gentoo.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@gentoo.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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