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+
+
+ modedb default video mode support
+
+
+Currently all frame buffer device drivers have their own video mode databases,
+which is a mess and a waste of resources. The main idea of modedb is to have
+
+ - one routine to probe for video modes, which can be used by all frame buffer
+ devices
+ - one generic video mode database with a fair amount of standard videomodes
+ (taken from XFree86)
+ - the possibility to supply your own mode database for graphics hardware that
+ needs non-standard modes, like amifb and Mac frame buffer drivers (which
+ use macmodes.c)
+
+When a frame buffer device receives a video= option it doesn't know, it should
+consider that to be a video mode option. If no frame buffer device is specified
+in a video= option, fbmem considers that to be a global video mode option.
+
+Valid mode specifiers (mode_option argument):
+
+ <xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]
+ <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
+
+DRM drivers also add options to enable or disable outputs:
+
+'e' will force the display to be enabled, i.e. it will override the detection
+if a display is connected. 'D' will force the display to be enabled and use
+digital output. This is useful for outputs that have both analog and digital
+signals (e.g. HDMI and DVI-I). For other outputs it behaves like 'e'. If 'd'
+is specified the output is disabled.
+
+You can additionally specify which output the options matches to.
+To force the VGA output to be enabled and drive a specific mode say:
+ video=VGA-1:1280x1024@60me
+
+Specifying the option multiple times for different ports is possible, e.g.:
+ video=LVDS-1:d video=HDMI-1:D
+
+***** 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,
+ struct fb_info *info, const char *mode_option,
+ const struct fb_videomode *db, unsigned int dbsize,
+ const struct fb_videomode *default_mode,
+ unsigned int default_bpp)
+
+with db/dbsize your non-standard video mode database, or NULL to use the
+standard video mode database.
+
+fb_find_mode() first tries the specified video mode (or any mode that matches,
+e.g. there can be multiple 640x480 modes, each of them is tried). If that
+fails, the default mode is tried. If that fails, it walks over all modes.
+
+To specify a video mode at bootup, use the following boot options:
+ video=<driver>:<xres>x<yres>[-<bpp>][@refresh]
+
+where <driver> is a name from the table below. Valid default modes can be
+found in linux/drivers/video/modedb.c. Check your driver's documentation.
+There may be more modes.
+
+ Drivers that support modedb boot options
+ Boot Name Cards Supported
+
+ amifb - Amiga chipset frame buffer
+ aty128fb - ATI Rage128 / Pro frame buffer
+ atyfb - ATI Mach64 frame buffer
+ pm2fb - Permedia 2/2V frame buffer
+ pm3fb - Permedia 3 frame buffer
+ sstfb - Voodoo 1/2 (SST1) chipset frame buffer
+ tdfxfb - 3D Fx frame buffer
+ tridentfb - Trident (Cyber)blade chipset frame buffer
+ vt8623fb - VIA 8623 frame buffer
+
+BTW, only a few fb drivers use this at the moment. Others are to follow
+(feel free to send patches). The DRM drivers also support this.