| ========================================================== | |
| uvesafb - A Generic Driver for VBE2+ compliant video cards | |
| ========================================================== | |
| 1. Requirements | |
| --------------- | |
| uvesafb should work with any video card that has a Video BIOS compliant | |
| with the VBE 2.0 standard. | |
| Unlike other drivers, uvesafb makes use of a userspace helper called | |
| v86d. v86d is used to run the x86 Video BIOS code in a simulated and | |
| controlled environment. This allows uvesafb to function on arches other | |
| than x86. Check the v86d documentation for a list of currently supported | |
| arches. | |
| v86d source code can be downloaded from the following website: | |
| https://github.com/mjanusz/v86d | |
| Please refer to the v86d documentation for detailed configuration and | |
| installation instructions. | |
| Note that the v86d userspace helper has to be available at all times in | |
| order for uvesafb to work properly. If you want to use uvesafb during | |
| early boot, you will have to include v86d into an initramfs image, and | |
| either compile it into the kernel or use it as an initrd. | |
| 2. Caveats and limitations | |
| -------------------------- | |
| uvesafb is a _generic_ driver which supports a wide variety of video | |
| cards, but which is ultimately limited by the Video BIOS interface. | |
| The most important limitations are: | |
| - Lack of any type of acceleration. | |
| - A strict and limited set of supported video modes. Often the native | |
| or most optimal resolution/refresh rate for your setup will not work | |
| with uvesafb, simply because the Video BIOS doesn't support the | |
| video mode you want to use. This can be especially painful with | |
| widescreen panels, where native video modes don't have the 4:3 aspect | |
| ratio, which is what most BIOS-es are limited to. | |
| - Adjusting the refresh rate is only possible with a VBE 3.0 compliant | |
| Video BIOS. Note that many nVidia Video BIOS-es claim to be VBE 3.0 | |
| compliant, while they simply ignore any refresh rate settings. | |
| 3. Configuration | |
| ---------------- | |
| uvesafb can be compiled either as a module, or directly into the kernel. | |
| In both cases it supports the same set of configuration options, which | |
| are either given on the kernel command line or as module parameters, e.g.:: | |
| video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel) | |
| # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap (module) | |
| Accepted options: | |
| ======= ========================================================= | |
| ypan Enable display panning using the VESA protected mode | |
| interface. The visible screen is just a window of the | |
| video memory, console scrolling is done by changing the | |
| start of the window. This option is available on x86 | |
| only and is the default option on that architecture. | |
| ywrap Same as ypan, but assumes your gfx board can wrap-around | |
| the video memory (i.e. starts reading from top if it | |
| reaches the end of video memory). Faster than ypan. | |
| Available on x86 only. | |
| redraw Scroll by redrawing the affected part of the screen, this | |
| is the default on non-x86. | |
| ======= ========================================================= | |
| (If you're using uvesafb as a module, the above three options are | |
| used a parameter of the scroll option, e.g. scroll=ypan.) | |
| =========== ==================================================================== | |
| vgapal Use the standard VGA registers for palette changes. | |
| pmipal Use the protected mode interface for palette changes. | |
| This is the default if the protected mode interface is | |
| available. Available on x86 only. | |
| mtrr:n Setup memory type range registers for the framebuffer | |
| where n: | |
| - 0 - disabled (equivalent to nomtrr) | |
| - 3 - write-combining (default) | |
| Values other than 0 and 3 will result in a warning and will be | |
| treated just like 3. | |
| nomtrr Do not use memory type range registers. | |
| vremap:n | |
| Remap 'n' MiB of video RAM. If 0 or not specified, remap memory | |
| according to video mode. | |
| vtotal:n If the video BIOS of your card incorrectly determines the total | |
| amount of video RAM, use this option to override the BIOS (in MiB). | |
| <mode> The mode you want to set, in the standard modedb format. Refer to | |
| modedb.txt for a detailed description. When uvesafb is compiled as | |
| a module, the mode string should be provided as a value of the | |
| 'mode_option' option. | |
| vbemode:x Force the use of VBE mode x. The mode will only be set if it's | |
| found in the VBE-provided list of supported modes. | |
| NOTE: The mode number 'x' should be specified in VESA mode number | |
| notation, not the Linux kernel one (eg. 257 instead of 769). | |
| HINT: If you use this option because normal <mode> parameter does | |
| not work for you and you use a X server, you'll probably want to | |
| set the 'nocrtc' option to ensure that the video mode is properly | |
| restored after console <-> X switches. | |
| nocrtc Do not use CRTC timings while setting the video mode. This option | |
| has any effect only if the Video BIOS is VBE 3.0 compliant. Use it | |
| if you have problems with modes set the standard way. Note that | |
| using this option implies that any refresh rate adjustments will | |
| be ignored and the refresh rate will stay at your BIOS default | |
| (60 Hz). | |
| noedid Do not try to fetch and use EDID-provided modes. | |
| noblank Disable hardware blanking. | |
| v86d:path Set path to the v86d executable. This option is only available as | |
| a module parameter, and not as a part of the video= string. If you | |
| need to use it and have uvesafb built into the kernel, use | |
| uvesafb.v86d="path". | |
| =========== ==================================================================== | |
| Additionally, the following parameters may be provided. They all override the | |
| EDID-provided values and BIOS defaults. Refer to your monitor's specs to get | |
| the correct values for maxhf, maxvf and maxclk for your hardware. | |
| =========== ====================================== | |
| maxhf:n Maximum horizontal frequency (in kHz). | |
| maxvf:n Maximum vertical frequency (in Hz). | |
| maxclk:n Maximum pixel clock (in MHz). | |
| =========== ====================================== | |
| 4. The sysfs interface | |
| ---------------------- | |
| uvesafb provides several sysfs nodes for configurable parameters and | |
| additional information. | |
| Driver attributes: | |
| /sys/bus/platform/drivers/uvesafb | |
| v86d | |
| (default: /sbin/v86d) | |
| Path to the v86d executable. v86d is started by uvesafb | |
| if an instance of the daemon isn't already running. | |
| Device attributes: | |
| /sys/bus/platform/drivers/uvesafb/uvesafb.0 | |
| nocrtc | |
| Use the default refresh rate (60 Hz) if set to 1. | |
| oem_product_name, oem_product_rev, oem_string, oem_vendor | |
| Information about the card and its maker. | |
| vbe_modes | |
| A list of video modes supported by the Video BIOS along with their | |
| VBE mode numbers in hex. | |
| vbe_version | |
| A BCD value indicating the implemented VBE standard. | |
| 5. Miscellaneous | |
| ---------------- | |
| Uvesafb will set a video mode with the default refresh rate and timings | |
| from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo. | |
| Michal Januszewski <spock@gentoo.org> | |
| Last updated: 2017-10-10 | |
| Documentation of the uvesafb options is loosely based on vesafb.txt. |