uvesafb.rst (7409B)
1========================================================== 2uvesafb - A Generic Driver for VBE2+ compliant video cards 3========================================================== 4 51. Requirements 6--------------- 7 8uvesafb should work with any video card that has a Video BIOS compliant 9with the VBE 2.0 standard. 10 11Unlike other drivers, uvesafb makes use of a userspace helper called 12v86d. v86d is used to run the x86 Video BIOS code in a simulated and 13controlled environment. This allows uvesafb to function on arches other 14than x86. Check the v86d documentation for a list of currently supported 15arches. 16 17v86d source code can be downloaded from the following website: 18 19 https://github.com/mjanusz/v86d 20 21Please refer to the v86d documentation for detailed configuration and 22installation instructions. 23 24Note that the v86d userspace helper has to be available at all times in 25order for uvesafb to work properly. If you want to use uvesafb during 26early boot, you will have to include v86d into an initramfs image, and 27either compile it into the kernel or use it as an initrd. 28 292. Caveats and limitations 30-------------------------- 31 32uvesafb is a _generic_ driver which supports a wide variety of video 33cards, but which is ultimately limited by the Video BIOS interface. 34The most important limitations are: 35 36- Lack of any type of acceleration. 37- A strict and limited set of supported video modes. Often the native 38 or most optimal resolution/refresh rate for your setup will not work 39 with uvesafb, simply because the Video BIOS doesn't support the 40 video mode you want to use. This can be especially painful with 41 widescreen panels, where native video modes don't have the 4:3 aspect 42 ratio, which is what most BIOS-es are limited to. 43- Adjusting the refresh rate is only possible with a VBE 3.0 compliant 44 Video BIOS. Note that many nVidia Video BIOS-es claim to be VBE 3.0 45 compliant, while they simply ignore any refresh rate settings. 46 473. Configuration 48---------------- 49 50uvesafb can be compiled either as a module, or directly into the kernel. 51In both cases it supports the same set of configuration options, which 52are either given on the kernel command line or as module parameters, e.g.:: 53 54 video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel) 55 56 # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap (module) 57 58Accepted options: 59 60======= ========================================================= 61ypan Enable display panning using the VESA protected mode 62 interface. The visible screen is just a window of the 63 video memory, console scrolling is done by changing the 64 start of the window. This option is available on x86 65 only and is the default option on that architecture. 66 67ywrap Same as ypan, but assumes your gfx board can wrap-around 68 the video memory (i.e. starts reading from top if it 69 reaches the end of video memory). Faster than ypan. 70 Available on x86 only. 71 72redraw Scroll by redrawing the affected part of the screen, this 73 is the default on non-x86. 74======= ========================================================= 75 76(If you're using uvesafb as a module, the above three options are 77used a parameter of the scroll option, e.g. scroll=ypan.) 78 79=========== ==================================================================== 80vgapal Use the standard VGA registers for palette changes. 81 82pmipal Use the protected mode interface for palette changes. 83 This is the default if the protected mode interface is 84 available. Available on x86 only. 85 86mtrr:n Setup memory type range registers for the framebuffer 87 where n: 88 89 - 0 - disabled (equivalent to nomtrr) 90 - 3 - write-combining (default) 91 92 Values other than 0 and 3 will result in a warning and will be 93 treated just like 3. 94 95nomtrr Do not use memory type range registers. 96 97vremap:n 98 Remap 'n' MiB of video RAM. If 0 or not specified, remap memory 99 according to video mode. 100 101vtotal:n If the video BIOS of your card incorrectly determines the total 102 amount of video RAM, use this option to override the BIOS (in MiB). 103 104<mode> The mode you want to set, in the standard modedb format. Refer to 105 modedb.txt for a detailed description. When uvesafb is compiled as 106 a module, the mode string should be provided as a value of the 107 'mode_option' option. 108 109vbemode:x Force the use of VBE mode x. The mode will only be set if it's 110 found in the VBE-provided list of supported modes. 111 NOTE: The mode number 'x' should be specified in VESA mode number 112 notation, not the Linux kernel one (eg. 257 instead of 769). 113 HINT: If you use this option because normal <mode> parameter does 114 not work for you and you use a X server, you'll probably want to 115 set the 'nocrtc' option to ensure that the video mode is properly 116 restored after console <-> X switches. 117 118nocrtc Do not use CRTC timings while setting the video mode. This option 119 has any effect only if the Video BIOS is VBE 3.0 compliant. Use it 120 if you have problems with modes set the standard way. Note that 121 using this option implies that any refresh rate adjustments will 122 be ignored and the refresh rate will stay at your BIOS default 123 (60 Hz). 124 125noedid Do not try to fetch and use EDID-provided modes. 126 127noblank Disable hardware blanking. 128 129v86d:path Set path to the v86d executable. This option is only available as 130 a module parameter, and not as a part of the video= string. If you 131 need to use it and have uvesafb built into the kernel, use 132 uvesafb.v86d="path". 133=========== ==================================================================== 134 135Additionally, the following parameters may be provided. They all override the 136EDID-provided values and BIOS defaults. Refer to your monitor's specs to get 137the correct values for maxhf, maxvf and maxclk for your hardware. 138 139=========== ====================================== 140maxhf:n Maximum horizontal frequency (in kHz). 141maxvf:n Maximum vertical frequency (in Hz). 142maxclk:n Maximum pixel clock (in MHz). 143=========== ====================================== 144 1454. The sysfs interface 146---------------------- 147 148uvesafb provides several sysfs nodes for configurable parameters and 149additional information. 150 151Driver attributes: 152 153/sys/bus/platform/drivers/uvesafb 154 v86d 155 (default: /sbin/v86d) 156 157 Path to the v86d executable. v86d is started by uvesafb 158 if an instance of the daemon isn't already running. 159 160Device attributes: 161 162/sys/bus/platform/drivers/uvesafb/uvesafb.0 163 nocrtc 164 Use the default refresh rate (60 Hz) if set to 1. 165 166 oem_product_name, oem_product_rev, oem_string, oem_vendor 167 Information about the card and its maker. 168 169 vbe_modes 170 A list of video modes supported by the Video BIOS along with their 171 VBE mode numbers in hex. 172 173 vbe_version 174 A BCD value indicating the implemented VBE standard. 175 1765. Miscellaneous 177---------------- 178 179Uvesafb will set a video mode with the default refresh rate and timings 180from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo. 181 182 183 184 Michal Januszewski <spock@gentoo.org> 185 186 Last updated: 2017-10-10 187 188 Documentation of the uvesafb options is loosely based on vesafb.txt.