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 - panel_orientation, one of "normal", "upside_down", "left_side_up", or 74 "right_side_up". For KMS drivers only, this sets the "panel orientation" 75 property on the kms connector as hint for kms users. 76 77 78----------------------------------------------------------------------------- 79 80What is the VESA(TM) Coordinated Video Timings (CVT)? 81===================================================== 82 83From the VESA(TM) Website: 84 85 "The purpose of CVT is to provide a method for generating a consistent 86 and coordinated set of standard formats, display refresh rates, and 87 timing specifications for computer display products, both those 88 employing CRTs, and those using other display technologies. The 89 intention of CVT is to give both source and display manufacturers a 90 common set of tools to enable new timings to be developed in a 91 consistent manner that ensures greater compatibility." 92 93This is the third standard approved by VESA(TM) concerning video timings. The 94first was the Discrete Video Timings (DVT) which is a collection of 95pre-defined modes approved by VESA(TM). The second is the Generalized Timing 96Formula (GTF) which is an algorithm to calculate the timings, given the 97pixelclock, the horizontal sync frequency, or the vertical refresh rate. 98 99The GTF is limited by the fact that it is designed mainly for CRT displays. 100It artificially increases the pixelclock because of its high blanking 101requirement. This is inappropriate for digital display interface with its high 102data rate which requires that it conserves the pixelclock as much as possible. 103Also, GTF does not take into account the aspect ratio of the display. 104 105The CVT addresses these limitations. If used with CRT's, the formula used 106is a derivation of GTF with a few modifications. If used with digital 107displays, the "reduced blanking" calculation can be used. 108 109From the framebuffer subsystem perspective, new formats need not be added 110to the global mode database whenever a new mode is released by display 111manufacturers. Specifying for CVT will work for most, if not all, relatively 112new CRT displays and probably with most flatpanels, if 'reduced blanking' 113calculation is specified. (The CVT compatibility of the display can be 114determined from its EDID. The version 1.3 of the EDID has extra 128-byte 115blocks where additional timing information is placed. As of this time, there 116is no support yet in the layer to parse this additional blocks.) 117 118CVT also introduced a new naming convention (should be seen from dmesg output):: 119 120 <pix>M<a>[-R] 121 122 where: pix = total amount of pixels in MB (xres x yres) 123 M = always present 124 a = aspect ratio (3 - 4:3; 4 - 5:4; 9 - 15:9, 16:9; A - 16:10) 125 -R = reduced blanking 126 127 example: .48M3-R - 800x600 with reduced blanking 128 129Note: VESA(TM) has restrictions on what is a standard CVT timing: 130 131 - aspect ratio can only be one of the above values 132 - acceptable refresh rates are 50, 60, 70 or 85 Hz only 133 - if reduced blanking, the refresh rate must be at 60Hz 134 135If one of the above are not satisfied, the kernel will print a warning but the 136timings will still be calculated. 137 138----------------------------------------------------------------------------- 139 140To find a suitable video mode, you just call:: 141 142 int __init fb_find_mode(struct fb_var_screeninfo *var, 143 struct fb_info *info, const char *mode_option, 144 const struct fb_videomode *db, unsigned int dbsize, 145 const struct fb_videomode *default_mode, 146 unsigned int default_bpp) 147 148with db/dbsize your non-standard video mode database, or NULL to use the 149standard video mode database. 150 151fb_find_mode() first tries the specified video mode (or any mode that matches, 152e.g. there can be multiple 640x480 modes, each of them is tried). If that 153fails, the default mode is tried. If that fails, it walks over all modes. 154 155To specify a video mode at bootup, use the following boot options:: 156 157 video=<driver>:<xres>x<yres>[-<bpp>][@refresh] 158 159where <driver> is a name from the table below. Valid default modes can be 160found in drivers/video/fbdev/core/modedb.c. Check your driver's documentation. 161There may be more modes:: 162 163 Drivers that support modedb boot options 164 Boot Name Cards Supported 165 166 amifb - Amiga chipset frame buffer 167 aty128fb - ATI Rage128 / Pro frame buffer 168 atyfb - ATI Mach64 frame buffer 169 pm2fb - Permedia 2/2V frame buffer 170 pm3fb - Permedia 3 frame buffer 171 sstfb - Voodoo 1/2 (SST1) chipset frame buffer 172 tdfxfb - 3D Fx frame buffer 173 tridentfb - Trident (Cyber)blade chipset frame buffer 174 vt8623fb - VIA 8623 frame buffer 175 176BTW, only a few fb drivers use this at the moment. Others are to follow 177(feel free to send patches). The DRM drivers also support this. 178