183 lines · plain
1=================================2modedb default video mode support3=================================4 5 6Currently all frame buffer device drivers have their own video mode databases,7which is a mess and a waste of resources. The main idea of modedb is to have8 9 - one routine to probe for video modes, which can be used by all frame buffer10 devices11 - one generic video mode database with a fair amount of standard videomodes12 (taken from XFree86)13 - the possibility to supply your own mode database for graphics hardware that14 needs non-standard modes, like amifb and Mac frame buffer drivers (which15 use macmodes.c)16 17When a frame buffer device receives a video= option it doesn't know, it should18consider that to be a video mode option. If no frame buffer device is specified19in a video= option, fbmem considers that to be a global video mode option.20 21Valid mode specifiers (mode_option argument)::22 23 <xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]24 <name>[-<bpp>][@<refresh>]25 26with <xres>, <yres>, <bpp> and <refresh> decimal numbers and <name> a string.27Things between square brackets are optional.28 29Valid names are::30 31 - NSTC: 480i output, with the CCIR System-M TV mode and NTSC color encoding32 - NTSC-J: 480i output, with the CCIR System-M TV mode, the NTSC color33 encoding, and a black level equal to the blanking level.34 - PAL: 576i output, with the CCIR System-B TV mode and PAL color encoding35 - PAL-M: 480i output, with the CCIR System-M TV mode and PAL color encoding36 37If 'M' is specified in the mode_option argument (after <yres> and before38<bpp> and <refresh>, if specified) the timings will be calculated using39VESA(TM) Coordinated Video Timings instead of looking up the mode from a table.40If 'R' is specified, do a 'reduced blanking' calculation for digital displays.41If 'i' is specified, calculate for an interlaced mode. And if 'm' is42specified, add margins to the calculation (1.8% of xres rounded down to 843pixels and 1.8% of yres).44 45 Sample usage: 1024x768M@60m - CVT timing with margins46 47DRM drivers also add options to enable or disable outputs:48 49'e' will force the display to be enabled, i.e. it will override the detection50if a display is connected. 'D' will force the display to be enabled and use51digital output. This is useful for outputs that have both analog and digital52signals (e.g. HDMI and DVI-I). For other outputs it behaves like 'e'. If 'd'53is specified the output is disabled.54 55You can additionally specify which output the options matches to.56To force the VGA output to be enabled and drive a specific mode say::57 58 video=VGA-1:1280x1024@60me59 60Specifying the option multiple times for different ports is possible, e.g.::61 62 video=LVDS-1:d video=HDMI-1:D63 64Options can also be passed after the mode, using commas as separator.65 66 Sample usage: 720x480,rotate=180 - 720x480 mode, rotated by 180 degrees67 68Valid options are::69 70 - margin_top, margin_bottom, margin_left, margin_right (integer):71 Number of pixels in the margins, typically to deal with overscan on TVs72 - reflect_x (boolean): Perform an axial symmetry on the X axis73 - reflect_y (boolean): Perform an axial symmetry on the Y axis74 - rotate (integer): Rotate the initial framebuffer by x75 degrees. Valid values are 0, 90, 180 and 270.76 - tv_mode: Analog TV mode. One of "NTSC", "NTSC-443", "NTSC-J", "PAL",77 "PAL-M", "PAL-N", or "SECAM".78 - panel_orientation, one of "normal", "upside_down", "left_side_up", or79 "right_side_up". For KMS drivers only, this sets the "panel orientation"80 property on the kms connector as hint for kms users.81 82 83-----------------------------------------------------------------------------84 85What is the VESA(TM) Coordinated Video Timings (CVT)?86=====================================================87 88From the VESA(TM) Website:89 90 "The purpose of CVT is to provide a method for generating a consistent91 and coordinated set of standard formats, display refresh rates, and92 timing specifications for computer display products, both those93 employing CRTs, and those using other display technologies. The94 intention of CVT is to give both source and display manufacturers a95 common set of tools to enable new timings to be developed in a96 consistent manner that ensures greater compatibility."97 98This is the third standard approved by VESA(TM) concerning video timings. The99first was the Discrete Video Timings (DVT) which is a collection of100pre-defined modes approved by VESA(TM). The second is the Generalized Timing101Formula (GTF) which is an algorithm to calculate the timings, given the102pixelclock, the horizontal sync frequency, or the vertical refresh rate.103 104The GTF is limited by the fact that it is designed mainly for CRT displays.105It artificially increases the pixelclock because of its high blanking106requirement. This is inappropriate for digital display interface with its high107data rate which requires that it conserves the pixelclock as much as possible.108Also, GTF does not take into account the aspect ratio of the display.109 110The CVT addresses these limitations. If used with CRT's, the formula used111is a derivation of GTF with a few modifications. If used with digital112displays, the "reduced blanking" calculation can be used.113 114From the framebuffer subsystem perspective, new formats need not be added115to the global mode database whenever a new mode is released by display116manufacturers. Specifying for CVT will work for most, if not all, relatively117new CRT displays and probably with most flatpanels, if 'reduced blanking'118calculation is specified. (The CVT compatibility of the display can be119determined from its EDID. The version 1.3 of the EDID has extra 128-byte120blocks where additional timing information is placed. As of this time, there121is no support yet in the layer to parse this additional blocks.)122 123CVT also introduced a new naming convention (should be seen from dmesg output)::124 125 <pix>M<a>[-R]126 127 where: pix = total amount of pixels in MB (xres x yres)128 M = always present129 a = aspect ratio (3 - 4:3; 4 - 5:4; 9 - 15:9, 16:9; A - 16:10)130 -R = reduced blanking131 132 example: .48M3-R - 800x600 with reduced blanking133 134Note: VESA(TM) has restrictions on what is a standard CVT timing:135 136 - aspect ratio can only be one of the above values137 - acceptable refresh rates are 50, 60, 70 or 85 Hz only138 - if reduced blanking, the refresh rate must be at 60Hz139 140If one of the above are not satisfied, the kernel will print a warning but the141timings will still be calculated.142 143-----------------------------------------------------------------------------144 145To find a suitable video mode, you just call::146 147 int __init fb_find_mode(struct fb_var_screeninfo *var,148 struct fb_info *info, const char *mode_option,149 const struct fb_videomode *db, unsigned int dbsize,150 const struct fb_videomode *default_mode,151 unsigned int default_bpp)152 153with db/dbsize your non-standard video mode database, or NULL to use the154standard video mode database.155 156fb_find_mode() first tries the specified video mode (or any mode that matches,157e.g. there can be multiple 640x480 modes, each of them is tried). If that158fails, the default mode is tried. If that fails, it walks over all modes.159 160To specify a video mode at bootup, use the following boot options::161 162 video=<driver>:<xres>x<yres>[-<bpp>][@refresh]163 164where <driver> is a name from the table below. Valid default modes can be165found in drivers/video/fbdev/core/modedb.c. Check your driver's documentation.166There may be more modes::167 168 Drivers that support modedb boot options169 Boot Name Cards Supported170 171 amifb - Amiga chipset frame buffer172 aty128fb - ATI Rage128 / Pro frame buffer173 atyfb - ATI Mach64 frame buffer174 pm2fb - Permedia 2/2V frame buffer175 pm3fb - Permedia 3 frame buffer176 sstfb - Voodoo 1/2 (SST1) chipset frame buffer177 tdfxfb - 3D Fx frame buffer178 tridentfb - Trident (Cyber)blade chipset frame buffer179 vt8623fb - VIA 8623 frame buffer180 181BTW, only a few fb drivers use this at the moment. Others are to follow182(feel free to send patches). The DRM drivers also support this.183