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 - NTSC-J: 480i output, with the CCIR System-M TV mode, the NTSC color 33 encoding, and a black level equal to the blanking level. 34 - PAL: 576i output, with the CCIR System-B TV mode and PAL color encoding 35 - PAL-M: 480i output, with the CCIR System-M TV mode and PAL color encoding 36 37If 'M' is specified in the mode_option argument (after <yres> and before 38<bpp> and <refresh>, if specified) the timings will be calculated using 39VESA(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' is 42specified, add margins to the calculation (1.8% of xres rounded down to 8 43pixels and 1.8% of yres). 44 45 Sample usage: 1024x768M@60m - CVT timing with margins 46 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 detection 50if a display is connected. 'D' will force the display to be enabled and use 51digital output. This is useful for outputs that have both analog and digital 52signals (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@60me 59 60Specifying the option multiple times for different ports is possible, e.g.:: 61 62 video=LVDS-1:d video=HDMI-1:D 63 64Options can also be passed after the mode, using commas as separator. 65 66 Sample usage: 720x480,rotate=180 - 720x480 mode, rotated by 180 degrees 67 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 TVs 72 - reflect_x (boolean): Perform an axial symmetry on the X axis 73 - reflect_y (boolean): Perform an axial symmetry on the Y axis 74 - rotate (integer): Rotate the initial framebuffer by x 75 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", or 79 "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 consistent 91 and coordinated set of standard formats, display refresh rates, and 92 timing specifications for computer display products, both those 93 employing CRTs, and those using other display technologies. The 94 intention of CVT is to give both source and display manufacturers a 95 common set of tools to enable new timings to be developed in a 96 consistent manner that ensures greater compatibility." 97 98This is the third standard approved by VESA(TM) concerning video timings. The 99first was the Discrete Video Timings (DVT) which is a collection of 100pre-defined modes approved by VESA(TM). The second is the Generalized Timing 101Formula (GTF) which is an algorithm to calculate the timings, given the 102pixelclock, 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 blanking 106requirement. This is inappropriate for digital display interface with its high 107data 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 used 111is a derivation of GTF with a few modifications. If used with digital 112displays, the "reduced blanking" calculation can be used. 113 114From the framebuffer subsystem perspective, new formats need not be added 115to the global mode database whenever a new mode is released by display 116manufacturers. Specifying for CVT will work for most, if not all, relatively 117new CRT displays and probably with most flatpanels, if 'reduced blanking' 118calculation is specified. (The CVT compatibility of the display can be 119determined from its EDID. The version 1.3 of the EDID has extra 128-byte 120blocks where additional timing information is placed. As of this time, there 121is 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 present 129 a = aspect ratio (3 - 4:3; 4 - 5:4; 9 - 15:9, 16:9; A - 16:10) 130 -R = reduced blanking 131 132 example: .48M3-R - 800x600 with reduced blanking 133 134Note: VESA(TM) has restrictions on what is a standard CVT timing: 135 136 - aspect ratio can only be one of the above values 137 - acceptable refresh rates are 50, 60, 70 or 85 Hz only 138 - if reduced blanking, the refresh rate must be at 60Hz 139 140If one of the above are not satisfied, the kernel will print a warning but the 141timings 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 the 154standard 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 that 158fails, 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 be 165found in drivers/video/fbdev/core/modedb.c. Check your driver's documentation. 166There may be more modes:: 167 168 Drivers that support modedb boot options 169 Boot Name Cards Supported 170 171 amifb - Amiga chipset frame buffer 172 aty128fb - ATI Rage128 / Pro frame buffer 173 atyfb - ATI Mach64 frame buffer 174 pm2fb - Permedia 2/2V frame buffer 175 pm3fb - Permedia 3 frame buffer 176 sstfb - Voodoo 1/2 (SST1) chipset frame buffer 177 tdfxfb - 3D Fx frame buffer 178 tridentfb - Trident (Cyber)blade chipset frame buffer 179 vt8623fb - VIA 8623 frame buffer 180 181BTW, only a few fb drivers use this at the moment. Others are to follow 182(feel free to send patches). The DRM drivers also support this. 183