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fb: add a new mode matching function fb_find_best_nearest_mode

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The intent is that if you have a native panel resolution of 1920x1080@60 but this cannot
be displayed, you can find the nearest resolution with the HIGHEST refresh rate (fb_find_nearest_mode
only selects the CLOSEST refresh rate). It also, by virtue of some rather unintended
side effect, picks better matches (1680x1050->1440x900) than find_nearest (1680x1050->1280x1024)
when it comes to widescreen modes.
This commit is contained in:
Matt Sealey
2011-06-13 19:51:55 -05:00
parent 54cf91e215
commit 5b7fe2afda
2 changed files with 59 additions and 0 deletions
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55
drivers/video/modedb.c
View File

@@ -900,6 +900,61 @@ const struct fb_videomode *fb_find_nearest_mode(const struct fb_videomode *mode,
return best;
}
/**
* fb_find_best_nearest_mode - find closest videomode a different way
*
* @mode: pointer to struct fb_videomode
* @head: pointer to modelist
*
* Finds best matching videomode, smaller or equal in dimension, with the
* highest refresh rate (specifically designed to service LCD panels with
* a maximum screen size == native panel size, and all other modes being
* smaller, or at least the same but with a lower refresh for pixelclock
* limited devices. e.g. 1080p24 instead of 1080p60, or 1440x900@60 instead
* of 1680x1050@72 - proper selection of mode is dependent on a properly
* sanitized modelist with any invalid/undisplayable modes removed.)
*
* This is a kind of works-best amalgam of find_best_mode (which operates on
* fb_var_screeninfo which is silly, but is concerned about the highest and
* therefore least flickery refresh rate) and find_nearest_mode (which is
* also looking for a mode bigger than the passed one, and seems not to pick
* the greatest mode in the vast majority of cases)
*
*/
const struct fb_videomode *fb_find_best_nearest_mode(const struct fb_videomode *mode,
struct list_head *head)
{
struct list_head *pos;
struct fb_modelist *modelist;
struct fb_videomode *cmode, *best = NULL;
u32 diff = -1;
list_for_each(pos, head) {
u32 d;
modelist = list_entry(pos, struct fb_modelist, list);
cmode = &modelist->mode;
/* the calculations here assume that every other mode than the one
passed is somewhat smaller :) */
if (mode->xres >= cmode->xres && mode->yres >= cmode->yres) {
d = abs(mode->xres - cmode->xres) +
abs(mode->yres - cmode->yres);
if (diff > d) {
/* as d grows smaller, best gets closer to the
* passed mode */
diff = d;
best = cmode;
} else if (diff == d && best &&
mode->refresh > best->refresh) {
best = cmode;
}
}
}
return best;
}
/**
* fb_match_mode - find a videomode which exactly matches the timings in var
* @var: pointer to struct fb_var_screeninfo

4
include/linux/fb.h
View File

@@ -1080,8 +1080,12 @@ extern const struct fb_videomode *fb_match_mode(const struct fb_var_screeninfo *
struct list_head *head);
extern const struct fb_videomode *fb_find_best_mode(const struct fb_var_screeninfo *var,
struct list_head *head);
extern const struct fb_videomode *fb_find_best_nearest_mode(const struct fb_videomode *mode,
struct list_head *head);
extern const struct fb_videomode *fb_find_nearest_mode(const struct fb_videomode *mode,
struct list_head *head);
extern void fb_destroy_modelist(struct list_head *head);
extern void fb_videomode_to_modelist(const struct fb_videomode *modedb, int num,
struct list_head *head);