1================================= 2modedb default video mode support 3================================= 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 have 8 9 - one routine to probe for video modes, which can be used by all frame buffer 10 devices 11 - one generic video mode database with a fair amount of standard videomodes 12 (taken from XFree86) 13 - the possibility to supply your own mode database for graphics hardware that 14 needs non-standard modes, like amifb and Mac frame buffer drivers (which 15 use macmodes.c) 16 17When a frame buffer device receives a video= option it doesn't know, it should 18consider that to be a video mode option. If no frame buffer device is specified 19in 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 encoding 32 - PAL: 576i output, with the CCIR System-B TV mode and PAL color encoding 33 34If 'M' is specified in the mode_option argument (after <yres> and before 35<bpp> and <refresh>, if specified) the timings will be calculated using 36VESA(TM) Coordinated Video Timings instead of looking up the mode from a table. 37If 'R' is specified, do a 'reduced blanking' calculation for digital displays. 38If 'i' is specified, calculate for an interlaced mode. And if 'm' is 39specified, add margins to the calculation (1.8% of xres rounded down to 8 40pixels and 1.8% of yres). 41 42 Sample usage: 1024x768M@60m - CVT timing with margins 43 44DRM drivers also add options to enable or disable outputs: 45 46'e' will force the display to be enabled, i.e. it will override the detection 47if a display is connected. 'D' will force the display to be enabled and use 48digital output. This is useful for outputs that have both analog and digital 49signals (e.g. HDMI and DVI-I). For other outputs it behaves like 'e'. If 'd' 50is specified the output is disabled. 51 52You can additionally specify which output the options matches to. 53To force the VGA output to be enabled and drive a specific mode say:: 54 55 video=VGA-1:1280x1024@60me 56 57Specifying the option multiple times for different ports is possible, e.g.:: 58 59 video=LVDS-1:d video=HDMI-1:D 60 61Options can also be passed after the mode, using commas as separator. 62 63 Sample usage: 720x480,rotate=180 - 720x480 mode, rotated by 180 degrees 64 65Valid options are:: 66 67 - margin_top, margin_bottom, margin_left, margin_right (integer): 68 Number of pixels in the margins, typically to deal with overscan on TVs 69 - reflect_x (boolean): Perform an axial symmetry on the X axis 70 - reflect_y (boolean): Perform an axial symmetry on the Y axis 71 - rotate (integer): Rotate the initial framebuffer by x 72 degrees. Valid values are 0, 90, 180 and 270. 73 - tv_mode: Analog TV mode. One of "NTSC", "NTSC-443", "NTSC-J", "PAL", 74 "PAL-M", "PAL-N", or "SECAM". 75 - panel_orientation, one of "normal", "upside_down", "left_side_up", or 76 "right_side_up". For KMS drivers only, this sets the "panel orientation" 77 property on the kms connector as hint for kms users. 78 79 80----------------------------------------------------------------------------- 81 82What is the VESA(TM) Coordinated Video Timings (CVT)? 83===================================================== 84 85From the VESA(TM) Website: 86 87 "The purpose of CVT is to provide a method for generating a consistent 88 and coordinated set of standard formats, display refresh rates, and 89 timing specifications for computer display products, both those 90 employing CRTs, and those using other display technologies. The 91 intention of CVT is to give both source and display manufacturers a 92 common set of tools to enable new timings to be developed in a 93 consistent manner that ensures greater compatibility." 94 95This is the third standard approved by VESA(TM) concerning video timings. The 96first was the Discrete Video Timings (DVT) which is a collection of 97pre-defined modes approved by VESA(TM). The second is the Generalized Timing 98Formula (GTF) which is an algorithm to calculate the timings, given the 99pixelclock, the horizontal sync frequency, or the vertical refresh rate. 100 101The GTF is limited by the fact that it is designed mainly for CRT displays. 102It artificially increases the pixelclock because of its high blanking 103requirement. This is inappropriate for digital display interface with its high 104data rate which requires that it conserves the pixelclock as much as possible. 105Also, GTF does not take into account the aspect ratio of the display. 106 107The CVT addresses these limitations. If used with CRT's, the formula used 108is a derivation of GTF with a few modifications. If used with digital 109displays, the "reduced blanking" calculation can be used. 110 111From the framebuffer subsystem perspective, new formats need not be added 112to the global mode database whenever a new mode is released by display 113manufacturers. Specifying for CVT will work for most, if not all, relatively 114new CRT displays and probably with most flatpanels, if 'reduced blanking' 115calculation is specified. (The CVT compatibility of the display can be 116determined from its EDID. The version 1.3 of the EDID has extra 128-byte 117blocks where additional timing information is placed. As of this time, there 118is no support yet in the layer to parse this additional blocks.) 119 120CVT also introduced a new naming convention (should be seen from dmesg output):: 121 122 <pix>M<a>[-R] 123 124 where: pix = total amount of pixels in MB (xres x yres) 125 M = always present 126 a = aspect ratio (3 - 4:3; 4 - 5:4; 9 - 15:9, 16:9; A - 16:10) 127 -R = reduced blanking 128 129 example: .48M3-R - 800x600 with reduced blanking 130 131Note: VESA(TM) has restrictions on what is a standard CVT timing: 132 133 - aspect ratio can only be one of the above values 134 - acceptable refresh rates are 50, 60, 70 or 85 Hz only 135 - if reduced blanking, the refresh rate must be at 60Hz 136 137If one of the above are not satisfied, the kernel will print a warning but the 138timings will still be calculated. 139 140----------------------------------------------------------------------------- 141 142To find a suitable video mode, you just call:: 143 144 int __init fb_find_mode(struct fb_var_screeninfo *var, 145 struct fb_info *info, const char *mode_option, 146 const struct fb_videomode *db, unsigned int dbsize, 147 const struct fb_videomode *default_mode, 148 unsigned int default_bpp) 149 150with db/dbsize your non-standard video mode database, or NULL to use the 151standard video mode database. 152 153fb_find_mode() first tries the specified video mode (or any mode that matches, 154e.g. there can be multiple 640x480 modes, each of them is tried). If that 155fails, the default mode is tried. If that fails, it walks over all modes. 156 157To specify a video mode at bootup, use the following boot options:: 158 159 video=<driver>:<xres>x<yres>[-<bpp>][@refresh] 160 161where <driver> is a name from the table below. Valid default modes can be 162found in drivers/video/fbdev/core/modedb.c. Check your driver's documentation. 163There may be more modes:: 164 165 Drivers that support modedb boot options 166 Boot Name Cards Supported 167 168 amifb - Amiga chipset frame buffer 169 aty128fb - ATI Rage128 / Pro frame buffer 170 atyfb - ATI Mach64 frame buffer 171 pm2fb - Permedia 2/2V frame buffer 172 pm3fb - Permedia 3 frame buffer 173 sstfb - Voodoo 1/2 (SST1) chipset frame buffer 174 tdfxfb - 3D Fx frame buffer 175 tridentfb - Trident (Cyber)blade chipset frame buffer 176 vt8623fb - VIA 8623 frame buffer 177 178BTW, only a few fb drivers use this at the moment. Others are to follow 179(feel free to send patches). The DRM drivers also support this. 180