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