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[PATCH] fbdev: Add VESA Coordinated Video Timings (CVT) support 

The Coordinated Video Timings (CVT) is the latest standard approved by VESA
concerning video timings generation.  It addresses the limitation of GTF which
is designed mainly for CRT displays.  CRT's have a high blanking requirement
(as much as 25% of the horizontal frame length) which artificially increases
the pixelclock.  Digital displays, on the other hand, needs to conserve the
pixelclock as much as possible.  The GTF also does not take into account the
different aspect ratios in its calculation.

The new function added is fb_find_mode_cvt().  It is called by fb_find_mode()
if it recognizes a mode option string formatted for CVT.  The format is:

<xres>x<yres>[M][R][-<bpp>][<at-sign><refresh>][i][m]

The 'M' tells the function to calculate using CVT.  On it's own, it will
compute a timing for CRT displays at 60Hz.  If the 'R' is specified, 'reduced
blanking' computation will be used, best for flatpanels.  The 'i' and the 'm'
is for 'interlaced mode' and 'with margins' respectively.

To determine if CVT was used, check for dmesg for something like this:

CVT Mode - <pix>M<n>[-R], ie: .480M3-R  (800x600 reduced blanking)

where: pix - product of xres and yres, in MB
    M   - is a CVT mode
    n   - the aspect ratio (3 - 4:3; 4 - 5:4; 9 - 16:9, 15:9; A - 16:10)
    -R   - reduced blanking

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Antonino A. Daplas 2005-09-09 13:09:58 -07:00 committed by Linus Torvalds
parent 5251bffc9b
commit 96fe6a2109
6 changed files with 519 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
Documentation/fb/modedb.txt
View File

@ -20,12 +20,83 @@ in a video= option, fbmem considers that to be a global video mode option.
Valid mode specifiers (mode_option argument):
<xres>x<yres>[-<bpp>][@<refresh>]
<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m]
<name>[-<bpp>][@<refresh>]
with <xres>, <yres>, <bpp> and <refresh> decimal numbers and <name> a string.
Things between square brackets are optional.
If 'M' is specified in the mode_option argument (after <yres> and before
<bpp> and <refresh>, if specified) the timings will be calculated using
VESA(TM) Coordinated Video Timings instead of looking up the mode from a table.
If 'R' is specified, do a 'reduced blanking' calculation for digital displays.
If 'i' is specified, calculate for an interlaced mode. And if 'm' is
specified, add margins to the calculation (1.8% of xres rounded down to 8
pixels and 1.8% of yres).
Sample usage: 1024x768M@60m - CVT timing with margins
***** oOo ***** oOo ***** oOo ***** oOo ***** oOo ***** oOo ***** oOo *****
What is the VESA(TM) Coordinated Video Timings (CVT)?
From the VESA(TM) Website:
"The purpose of CVT is to provide a method for generating a consistent
and coordinated set of standard formats, display refresh rates, and
timing specifications for computer display products, both those
employing CRTs, and those using other display technologies. The
intention of CVT is to give both source and display manufacturers a
common set of tools to enable new timings to be developed in a
consistent manner that ensures greater compatibility."
This is the third standard approved by VESA(TM) concerning video timings. The
first was the Discrete Video Timings (DVT) which is a collection of
pre-defined modes approved by VESA(TM). The second is the Generalized Timing
Formula (GTF) which is an algorithm to calculate the timings, given the
pixelclock, the horizontal sync frequency, or the vertical refresh rate.
The GTF is limited by the fact that it is designed mainly for CRT displays.
It artificially increases the pixelclock because of its high blanking
requirement. This is inappropriate for digital display interface with its high
data rate which requires that it conserves the pixelclock as much as possible.
Also, GTF does not take into account the aspect ratio of the display.
The CVT addresses these limitations. If used with CRT's, the formula used
is a derivation of GTF with a few modifications. If used with digital
displays, the "reduced blanking" calculation can be used.
From the framebuffer subsystem perspective, new formats need not be added
to the global mode database whenever a new mode is released by display
manufacturers. Specifying for CVT will work for most, if not all, relatively
new CRT displays and probably with most flatpanels, if 'reduced blanking'
calculation is specified. (The CVT compatibility of the display can be
determined from its EDID. The version 1.3 of the EDID has extra 128-byte
blocks where additional timing information is placed. As of this time, there
is no support yet in the layer to parse this additional blocks.)
CVT also introduced a new naming convention (should be seen from dmesg output):
<pix>M<a>[-R]
where: pix = total amount of pixels in MB (xres x yres)
M = always present
a = aspect ratio (3 - 4:3; 4 - 5:4; 9 - 15:9, 16:9; A - 16:10)
-R = reduced blanking
example: .48M3-R - 800x600 with reduced blanking
Note: VESA(TM) has restrictions on what is a standard CVT timing:
- aspect ratio can only be one of the above values
- acceptable refresh rates are 50, 60, 70 or 85 Hz only
- if reduced blanking, the refresh rate must be at 60Hz
If one of the above are not satisfied, the kernel will print a warning but the
timings will still be calculated.
***** oOo ***** oOo ***** oOo ***** oOo ***** oOo ***** oOo ***** oOo *****
To find a suitable video mode, you just call
int __init fb_find_mode(struct fb_var_screeninfo *var,

3
drivers/video/Makefile
View File

@ -9,7 +9,8 @@ obj-$(CONFIG_LOGO) += logo/
obj-$(CONFIG_SYSFS) += backlight/
obj-$(CONFIG_FB) += fb.o
fb-y := fbmem.o fbmon.o fbcmap.o fbsysfs.o modedb.o
fb-y := fbmem.o fbmon.o fbcmap.o fbsysfs.o \
modedb.o fbcvt.o
fb-objs := $(fb-y)
obj-$(CONFIG_FB_CFB_FILLRECT) += cfbfillrect.o

380
drivers/video/fbcvt.c Normal file
View File

@ -0,0 +1,380 @@
/*
* linux/drivers/video/fbcvt.c - VESA(TM) Coordinated Video Timings
*
* Copyright (C) 2005 Antonino Daplas <adaplas@pol.net>
*
* Based from the VESA(TM) Coordinated Video Timing Generator by
* Graham Loveridge April 9, 2003 available at
* http://www.vesa.org/public/CVT/CVTd6r1.xls
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file COPYING in the main directory of this archive
* for more details.
*
*/
#include <linux/fb.h>
#define FB_CVT_CELLSIZE 8
#define FB_CVT_GTF_C 40
#define FB_CVT_GTF_J 20
#define FB_CVT_GTF_K 128
#define FB_CVT_GTF_M 600
#define FB_CVT_MIN_VSYNC_BP 550
#define FB_CVT_MIN_VPORCH 3
#define FB_CVT_MIN_BPORCH 6
#define FB_CVT_RB_MIN_VBLANK 460
#define FB_CVT_RB_HBLANK 160
#define FB_CVT_RB_V_FPORCH 3
#define FB_CVT_FLAG_REDUCED_BLANK 1
#define FB_CVT_FLAG_MARGINS 2
#define FB_CVT_FLAG_INTERLACED 4
struct fb_cvt_data {
u32 xres;
u32 yres;
u32 refresh;
u32 f_refresh;
u32 pixclock;
u32 hperiod;
u32 hblank;
u32 hfreq;
u32 htotal;
u32 vtotal;
u32 vsync;
u32 hsync;
u32 h_front_porch;
u32 h_back_porch;
u32 v_front_porch;
u32 v_back_porch;
u32 h_margin;
u32 v_margin;
u32 interlace;
u32 aspect_ratio;
u32 active_pixels;
u32 flags;
u32 status;
};
static int fb_cvt_vbi_tab[] = {
4, /* 4:3 */
5, /* 16:9 */
6, /* 16:10 */
7, /* 5:4 */
7, /* 15:9 */
8, /* reserved */
9, /* reserved */
10 /* custom */
};
/* returns hperiod * 1000 */
static u32 fb_cvt_hperiod(struct fb_cvt_data *cvt)
{
u32 num = 1000000000/cvt->f_refresh;
u32 den;
if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK) {
num -= FB_CVT_RB_MIN_VBLANK * 1000;
den = 2 * (cvt->yres/cvt->interlace + 2 * cvt->v_margin);
} else {
num -= FB_CVT_MIN_VSYNC_BP * 1000;
den = 2 * (cvt->yres/cvt->interlace + cvt->v_margin * 2
+ FB_CVT_MIN_VPORCH + cvt->interlace/2);
}
return 2 * (num/den);
}
/* returns ideal duty cycle * 1000 */
static u32 fb_cvt_ideal_duty_cycle(struct fb_cvt_data *cvt)
{
u32 c_prime = (FB_CVT_GTF_C - FB_CVT_GTF_J) *
(FB_CVT_GTF_K) + 256 * FB_CVT_GTF_J;
u32 m_prime = (FB_CVT_GTF_K * FB_CVT_GTF_M);
u32 h_period_est = cvt->hperiod;
return (1000 * c_prime - ((m_prime * h_period_est)/1000))/256;
}
static u32 fb_cvt_hblank(struct fb_cvt_data *cvt)
{
u32 hblank = 0;
if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
hblank = FB_CVT_RB_HBLANK;
else {
u32 ideal_duty_cycle = fb_cvt_ideal_duty_cycle(cvt);
u32 active_pixels = cvt->active_pixels;
if (ideal_duty_cycle < 20000)
hblank = (active_pixels * 20000)/
(100000 - 20000);
else {
hblank = (active_pixels * ideal_duty_cycle)/
(100000 - ideal_duty_cycle);
}
}
hblank &= ~((2 * FB_CVT_CELLSIZE) - 1);
return hblank;
}
static u32 fb_cvt_hsync(struct fb_cvt_data *cvt)
{
u32 hsync;
if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
hsync = 32;
else
hsync = (FB_CVT_CELLSIZE * cvt->htotal)/100;
hsync &= ~(FB_CVT_CELLSIZE - 1);
return hsync;
}
static u32 fb_cvt_vbi_lines(struct fb_cvt_data *cvt)
{
u32 vbi_lines, min_vbi_lines, act_vbi_lines;
if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK) {
vbi_lines = (1000 * FB_CVT_RB_MIN_VBLANK)/cvt->hperiod + 1;
min_vbi_lines = FB_CVT_RB_V_FPORCH + cvt->vsync +
FB_CVT_MIN_BPORCH;
} else {
vbi_lines = (FB_CVT_MIN_VSYNC_BP * 1000)/cvt->hperiod + 1 +
FB_CVT_MIN_VPORCH;
min_vbi_lines = cvt->vsync + FB_CVT_MIN_BPORCH +
FB_CVT_MIN_VPORCH;
}
if (vbi_lines < min_vbi_lines)
act_vbi_lines = min_vbi_lines;
else
act_vbi_lines = vbi_lines;
return act_vbi_lines;
}
static u32 fb_cvt_vtotal(struct fb_cvt_data *cvt)
{
u32 vtotal = cvt->yres/cvt->interlace;
vtotal += 2 * cvt->v_margin + cvt->interlace/2 + fb_cvt_vbi_lines(cvt);
vtotal |= cvt->interlace/2;
return vtotal;
}
static u32 fb_cvt_pixclock(struct fb_cvt_data *cvt)
{
u32 pixclock;
if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
pixclock = (cvt->f_refresh * cvt->vtotal * cvt->htotal)/1000;
else
pixclock = (cvt->htotal * 1000000)/cvt->hperiod;
pixclock /= 250;
pixclock *= 250;
pixclock *= 1000;
return pixclock;
}
static u32 fb_cvt_aspect_ratio(struct fb_cvt_data *cvt)
{
u32 xres = cvt->xres;
u32 yres = cvt->yres;
u32 aspect = -1;
if (xres == (yres * 4)/3 && !((yres * 4) % 3))
aspect = 0;
else if (xres == (yres * 16)/9 && !((yres * 16) % 9))
aspect = 1;
else if (xres == (yres * 16)/10 && !((yres * 16) % 10))
aspect = 2;
else if (xres == (yres * 5)/4 && !((yres * 5) % 4))
aspect = 3;
else if (xres == (yres * 15)/9 && !((yres * 15) % 9))
aspect = 4;
else {
printk(KERN_INFO "fbcvt: Aspect ratio not CVT "
"standard\n");
aspect = 7;
cvt->status = 1;
}
return aspect;
}
static void fb_cvt_print_name(struct fb_cvt_data *cvt)
{
u32 pixcount, pixcount_mod;
int cnt = 255, offset = 0, read = 0;
u8 *buf = kmalloc(256, GFP_KERNEL);
if (!buf)
return;
memset(buf, 0, 256);
pixcount = (cvt->xres * (cvt->yres/cvt->interlace))/1000000;
pixcount_mod = (cvt->xres * (cvt->yres/cvt->interlace)) % 1000000;
pixcount_mod /= 1000;
read = snprintf(buf+offset, cnt, "fbcvt: %dx%d@%d: CVT Name - ",
cvt->xres, cvt->yres, cvt->refresh);
offset += read;
cnt -= read;
if (cvt->status)
snprintf(buf+offset, cnt, "Not a CVT standard - %d.%03d Mega "
"Pixel Image\n", pixcount, pixcount_mod);
else {
if (pixcount) {
read = snprintf(buf+offset, cnt, "%d", pixcount);
cnt -= read;
offset += read;
}
read = snprintf(buf+offset, cnt, ".%03dM", pixcount_mod);
cnt -= read;
offset += read;
if (cvt->aspect_ratio == 0)
read = snprintf(buf+offset, cnt, "3");
else if (cvt->aspect_ratio == 3)
read = snprintf(buf+offset, cnt, "4");
else if (cvt->aspect_ratio == 1 || cvt->aspect_ratio == 4)
read = snprintf(buf+offset, cnt, "9");
else if (cvt->aspect_ratio == 2)
read = snprintf(buf+offset, cnt, "A");
else
read = 0;
cnt -= read;
offset += read;
if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK) {
read = snprintf(buf+offset, cnt, "-R");
cnt -= read;
offset += read;
}
}
printk(KERN_INFO "%s\n", buf);
kfree(buf);
}
static void fb_cvt_convert_to_mode(struct fb_cvt_data *cvt,
struct fb_videomode *mode)
{
mode->refresh = cvt->f_refresh;
mode->pixclock = KHZ2PICOS(cvt->pixclock/1000);
mode->left_margin = cvt->h_front_porch;
mode->right_margin = cvt->h_back_porch;
mode->hsync_len = cvt->hsync;
mode->upper_margin = cvt->v_front_porch;
mode->lower_margin = cvt->v_back_porch;
mode->vsync_len = cvt->vsync;
mode->sync &= ~(FB_SYNC_HOR_HIGH_ACT | FB_SYNC_VERT_HIGH_ACT);
if (cvt->flags & FB_CVT_FLAG_REDUCED_BLANK)
mode->sync |= FB_SYNC_HOR_HIGH_ACT;
else
mode->sync |= FB_SYNC_VERT_HIGH_ACT;
}
/*
* fb_find_mode_cvt - calculate mode using VESA(TM) CVT
* @mode: pointer to fb_videomode; xres, yres, refresh and vmode must be
* pre-filled with the desired values
* @margins: add margin to calculation (1.8% of xres and yres)
* @rb: compute with reduced blanking (for flatpanels)
*
* RETURNS:
* 0 for success
* @mode is filled with computed values. If interlaced, the refresh field
* will be filled with the field rate (2x the frame rate)
*
* DESCRIPTION:
* Computes video timings using VESA(TM) Coordinated Video Timings
*/
int fb_find_mode_cvt(struct fb_videomode *mode, int margins, int rb)
{
struct fb_cvt_data cvt;
memset(&cvt, 0, sizeof(cvt));
if (margins)
cvt.flags |= FB_CVT_FLAG_MARGINS;
if (rb)
cvt.flags |= FB_CVT_FLAG_REDUCED_BLANK;
if (mode->vmode & FB_VMODE_INTERLACED)
cvt.flags |= FB_CVT_FLAG_INTERLACED;
cvt.xres = mode->xres;
cvt.yres = mode->yres;
cvt.refresh = mode->refresh;
cvt.f_refresh = cvt.refresh;
cvt.interlace = 1;
if (!cvt.xres || !cvt.yres || !cvt.refresh) {
printk(KERN_INFO "fbcvt: Invalid input parameters\n");
return 1;
}
if (!(cvt.refresh == 50 || cvt.refresh == 60 || cvt.refresh == 70 ||
cvt.refresh == 85)) {
printk(KERN_INFO "fbcvt: Refresh rate not CVT "
"standard\n");
cvt.status = 1;
}
cvt.xres &= ~(FB_CVT_CELLSIZE - 1);
if (cvt.flags & FB_CVT_FLAG_INTERLACED) {
cvt.interlace = 2;
cvt.f_refresh *= 2;
}
if (cvt.flags & FB_CVT_FLAG_REDUCED_BLANK) {
if (cvt.refresh != 60) {
printk(KERN_INFO "fbcvt: 60Hz refresh rate "
"advised for reduced blanking\n");
cvt.status = 1;
}
}
if (cvt.flags & FB_CVT_FLAG_MARGINS) {
cvt.h_margin = (cvt.xres * 18)/1000;
cvt.h_margin &= ~(FB_CVT_CELLSIZE - 1);
cvt.v_margin = ((cvt.yres/cvt.interlace)* 18)/1000;
}
cvt.aspect_ratio = fb_cvt_aspect_ratio(&cvt);
cvt.active_pixels = cvt.xres + 2 * cvt.h_margin;
cvt.hperiod = fb_cvt_hperiod(&cvt);
cvt.vsync = fb_cvt_vbi_tab[cvt.aspect_ratio];
cvt.vtotal = fb_cvt_vtotal(&cvt);
cvt.hblank = fb_cvt_hblank(&cvt);
cvt.htotal = cvt.active_pixels + cvt.hblank;
cvt.hsync = fb_cvt_hsync(&cvt);
cvt.pixclock = fb_cvt_pixclock(&cvt);
cvt.hfreq = cvt.pixclock/cvt.htotal;
cvt.h_back_porch = cvt.hblank/2 + cvt.h_margin;
cvt.h_front_porch = cvt.hblank - cvt.hsync - cvt.h_back_porch +
2 * cvt.h_margin;
cvt.v_back_porch = 3 + cvt.v_margin;
cvt.v_front_porch = cvt.vtotal - cvt.yres/cvt.interlace -
cvt.v_back_porch - cvt.vsync;
fb_cvt_print_name(&cvt);
fb_cvt_convert_to_mode(&cvt, mode);
return 0;
}
EXPORT_SYMBOL(fb_find_mode_cvt);

12
drivers/video/fbmem.c
View File

@ -1029,6 +1029,7 @@ register_framebuffer(struct fb_info *fb_info)
{
int i;
struct fb_event event;
struct fb_videomode mode;
if (num_registered_fb == FB_MAX)
return -ENXIO;
@ -1059,16 +1060,11 @@ register_framebuffer(struct fb_info *fb_info)
}
fb_info->pixmap.offset = 0;
if (!fb_info->modelist.prev ||
!fb_info->modelist.next ||
list_empty(&fb_info->modelist)) {
struct fb_videomode mode;
if (!fb_info->modelist.prev || !fb_info->modelist.next)
INIT_LIST_HEAD(&fb_info->modelist);
fb_var_to_videomode(&mode, &fb_info->var);
fb_add_videomode(&mode, &fb_info->modelist);
}
fb_var_to_videomode(&mode, &fb_info->var);
fb_add_videomode(&mode, &fb_info->modelist);
registered_fb[i] = fb_info;
devfs_mk_cdev(MKDEV(FB_MAJOR, i),

62
drivers/video/modedb.c
View File

@ -456,12 +456,22 @@ static int fb_try_mode(struct fb_var_screeninfo *var, struct fb_info *info,
*
* Valid mode specifiers for @mode_option:
*
* <xres>x<yres>[-<bpp>][@<refresh>] or
* <xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m] or
* <name>[-<bpp>][@<refresh>]
*
* with <xres>, <yres>, <bpp> and <refresh> decimal numbers and
* <name> a string.
*
* If 'M' is present after yres (and before refresh/bpp if present),
* the function will compute the timings using VESA(tm) Coordinated
* Video Timings (CVT). If 'R' is present after 'M', will compute with
* reduced blanking (for flatpanels). If 'i' is present, compute
* interlaced mode. If 'm' is present, add margins equal to 1.8%
* of xres rounded down to 8 pixels, and 1.8% of yres. The char
* 'i' and 'm' must be after 'M' and 'R'. Example:
*
* 1024x768MR-8@60m - Reduced blank with margins at 60Hz.
*
* NOTE: The passed struct @var is _not_ cleared! This allows you
* to supply values for e.g. the grayscale and accel_flags fields.
*
@ -495,7 +505,7 @@ int fb_find_mode(struct fb_var_screeninfo *var,
unsigned int namelen = strlen(name);
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;
int yres_specified = 0, cvt = 0, rb = 0, interlace = 0, margins = 0;
u32 best, diff;
for (i = namelen-1; i >= 0; i--) {
@ -506,6 +516,8 @@ int fb_find_mode(struct fb_var_screeninfo *var,
!yres_specified) {
refresh = my_atoi(&name[i+1]);
refresh_specified = 1;
if (cvt || rb)
cvt = 0;
} else
goto done;
break;
@ -514,6 +526,8 @@ int fb_find_mode(struct fb_var_screeninfo *var,
if (!bpp_specified && !yres_specified) {
bpp = my_atoi(&name[i+1]);
bpp_specified = 1;
if (cvt || rb)
cvt = 0;
} else
goto done;
break;
@ -526,6 +540,22 @@ int fb_find_mode(struct fb_var_screeninfo *var,
break;
case '0'...'9':
break;
case 'M':
if (!yres_specified)
cvt = 1;
break;
case 'R':
if (!cvt)
rb = 1;
break;
case 'm':
if (!cvt)
margins = 1;
break;
case 'i':
if (!cvt)
interlace = 1;
break;
default:
goto done;
}
@ -535,6 +565,34 @@ int fb_find_mode(struct fb_var_screeninfo *var,
res_specified = 1;
}
done:
if (cvt) {
struct fb_videomode cvt_mode;
int ret;
DPRINTK("CVT mode %dx%d@%dHz%s%s%s\n", xres, yres,
(refresh) ? refresh : 60, (rb) ? " reduced blanking" :
"", (margins) ? " with margins" : "", (interlace) ?
" interlaced" : "");
cvt_mode.xres = xres;
cvt_mode.yres = yres;
cvt_mode.refresh = (refresh) ? refresh : 60;
if (interlace)
cvt_mode.vmode |= FB_VMODE_INTERLACED;
else
cvt_mode.vmode &= ~FB_VMODE_INTERLACED;
ret = fb_find_mode_cvt(&cvt_mode, margins, rb);
if (!ret && !fb_try_mode(var, info, &cvt_mode, bpp)) {
DPRINTK("modedb CVT: CVT mode ok\n");
return 1;
}
DPRINTK("CVT mode invalid, getting mode from database\n");
}
DPRINTK("Trying specified video mode%s %ix%i\n",
refresh_specified ? "" : " (ignoring refresh rate)", xres, yres);

1
include/linux/fb.h
View File

@ -866,6 +866,7 @@ extern const unsigned char *fb_firmware_edid(struct device *device);
extern void fb_edid_to_monspecs(unsigned char *edid,
struct fb_monspecs *specs);
extern void fb_destroy_modedb(struct fb_videomode *modedb);
extern int fb_find_mode_cvt(struct fb_videomode *mode, int margins, int rb);
/* drivers/video/modedb.c */
#define VESA_MODEDB_SIZE 34