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 29If 'M' is specified in the mode_option argument (after <yres> and before 30<bpp> and <refresh>, if specified) the timings will be calculated using 31VESA(TM) Coordinated Video Timings instead of looking up the mode from a table. 32If 'R' is specified, do a 'reduced blanking' calculation for digital displays. 33If 'i' is specified, calculate for an interlaced mode. And if 'm' is 34specified, add margins to the calculation (1.8% of xres rounded down to 8 35pixels and 1.8% of yres). 36 37 Sample usage: 1024x768M@60m - CVT timing with margins 38 39DRM drivers also add options to enable or disable outputs: 40 41'e' will force the display to be enabled, i.e. it will override the detection 42if a display is connected. 'D' will force the display to be enabled and use 43digital output. This is useful for outputs that have both analog and digital 44signals (e.g. HDMI and DVI-I). For other outputs it behaves like 'e'. If 'd' 45is specified the output is disabled. 46 47You can additionally specify which output the options matches to. 48To force the VGA output to be enabled and drive a specific mode say:: 49 50 video=VGA-1:1280x1024@60me 51 52Specifying the option multiple times for different ports is possible, e.g.:: 53 54 video=LVDS-1:d video=HDMI-1:D 55 56Options can also be passed after the mode, using commas as separator. 57 58 Sample usage: 720x480,rotate=180 - 720x480 mode, rotated by 180 degrees 59 60Valid options are:: 61 62 - margin_top, margin_bottom, margin_left, margin_right (integer): 63 Number of pixels in the margins, typically to deal with overscan on TVs 64 - reflect_x (boolean): Perform an axial symmetry on the X axis 65 - reflect_y (boolean): Perform an axial symmetry on the Y axis 66 - rotate (integer): Rotate the initial framebuffer by x 67 degrees. Valid values are 0, 90, 180 and 270. 68 - panel_orientation, one of "normal", "upside_down", "left_side_up", or 69 "right_side_up". For KMS drivers only, this sets the "panel orientation" 70 property on the kms connector as hint for kms users. 71 72 73----------------------------------------------------------------------------- 74 75What is the VESA(TM) Coordinated Video Timings (CVT)? 76===================================================== 77 78From the VESA(TM) Website: 79 80 "The purpose of CVT is to provide a method for generating a consistent 81 and coordinated set of standard formats, display refresh rates, and 82 timing specifications for computer display products, both those 83 employing CRTs, and those using other display technologies. The 84 intention of CVT is to give both source and display manufacturers a 85 common set of tools to enable new timings to be developed in a 86 consistent manner that ensures greater compatibility." 87 88This is the third standard approved by VESA(TM) concerning video timings. The 89first was the Discrete Video Timings (DVT) which is a collection of 90pre-defined modes approved by VESA(TM). The second is the Generalized Timing 91Formula (GTF) which is an algorithm to calculate the timings, given the 92pixelclock, the horizontal sync frequency, or the vertical refresh rate. 93 94The GTF is limited by the fact that it is designed mainly for CRT displays. 95It artificially increases the pixelclock because of its high blanking 96requirement. This is inappropriate for digital display interface with its high 97data rate which requires that it conserves the pixelclock as much as possible. 98Also, GTF does not take into account the aspect ratio of the display. 99 100The CVT addresses these limitations. If used with CRT's, the formula used 101is a derivation of GTF with a few modifications. If used with digital 102displays, the "reduced blanking" calculation can be used. 103 104From the framebuffer subsystem perspective, new formats need not be added 105to the global mode database whenever a new mode is released by display 106manufacturers. Specifying for CVT will work for most, if not all, relatively 107new CRT displays and probably with most flatpanels, if 'reduced blanking' 108calculation is specified. (The CVT compatibility of the display can be 109determined from its EDID. The version 1.3 of the EDID has extra 128-byte 110blocks where additional timing information is placed. As of this time, there 111is no support yet in the layer to parse this additional blocks.) 112 113CVT also introduced a new naming convention (should be seen from dmesg output):: 114 115 <pix>M<a>[-R] 116 117 where: pix = total amount of pixels in MB (xres x yres) 118 M = always present 119 a = aspect ratio (3 - 4:3; 4 - 5:4; 9 - 15:9, 16:9; A - 16:10) 120 -R = reduced blanking 121 122 example: .48M3-R - 800x600 with reduced blanking 123 124Note: VESA(TM) has restrictions on what is a standard CVT timing: 125 126 - aspect ratio can only be one of the above values 127 - acceptable refresh rates are 50, 60, 70 or 85 Hz only 128 - if reduced blanking, the refresh rate must be at 60Hz 129 130If one of the above are not satisfied, the kernel will print a warning but the 131timings will still be calculated. 132 133----------------------------------------------------------------------------- 134 135To find a suitable video mode, you just call:: 136 137 int __init fb_find_mode(struct fb_var_screeninfo *var, 138 struct fb_info *info, const char *mode_option, 139 const struct fb_videomode *db, unsigned int dbsize, 140 const struct fb_videomode *default_mode, 141 unsigned int default_bpp) 142 143with db/dbsize your non-standard video mode database, or NULL to use the 144standard video mode database. 145 146fb_find_mode() first tries the specified video mode (or any mode that matches, 147e.g. there can be multiple 640x480 modes, each of them is tried). If that 148fails, the default mode is tried. If that fails, it walks over all modes. 149 150To specify a video mode at bootup, use the following boot options:: 151 152 video=<driver>:<xres>x<yres>[-<bpp>][@refresh] 153 154where <driver> is a name from the table below. Valid default modes can be 155found in drivers/video/fbdev/core/modedb.c. Check your driver's documentation. 156There may be more modes:: 157 158 Drivers that support modedb boot options 159 Boot Name Cards Supported 160 161 amifb - Amiga chipset frame buffer 162 aty128fb - ATI Rage128 / Pro frame buffer 163 atyfb - ATI Mach64 frame buffer 164 pm2fb - Permedia 2/2V frame buffer 165 pm3fb - Permedia 3 frame buffer 166 sstfb - Voodoo 1/2 (SST1) chipset frame buffer 167 tdfxfb - 3D Fx frame buffer 168 tridentfb - Trident (Cyber)blade chipset frame buffer 169 vt8623fb - VIA 8623 frame buffer 170 171BTW, only a few fb drivers use this at the moment. Others are to follow 172(feel free to send patches). The DRM drivers also support this. 173