0001 ==========================================================
0002 uvesafb - A Generic Driver for VBE2+ compliant video cards
0003 ==========================================================
0004
0005 1. Requirements
0006 ---------------
0007
0008 uvesafb should work with any video card that has a Video BIOS compliant
0009 with the VBE 2.0 standard.
0010
0011 Unlike other drivers, uvesafb makes use of a userspace helper called
0012 v86d. v86d is used to run the x86 Video BIOS code in a simulated and
0013 controlled environment. This allows uvesafb to function on arches other
0014 than x86. Check the v86d documentation for a list of currently supported
0015 arches.
0016
0017 v86d source code can be downloaded from the following website:
0018
0019 https://github.com/mjanusz/v86d
0020
0021 Please refer to the v86d documentation for detailed configuration and
0022 installation instructions.
0023
0024 Note that the v86d userspace helper has to be available at all times in
0025 order for uvesafb to work properly. If you want to use uvesafb during
0026 early boot, you will have to include v86d into an initramfs image, and
0027 either compile it into the kernel or use it as an initrd.
0028
0029 2. Caveats and limitations
0030 --------------------------
0031
0032 uvesafb is a _generic_ driver which supports a wide variety of video
0033 cards, but which is ultimately limited by the Video BIOS interface.
0034 The most important limitations are:
0035
0036 - Lack of any type of acceleration.
0037 - A strict and limited set of supported video modes. Often the native
0038 or most optimal resolution/refresh rate for your setup will not work
0039 with uvesafb, simply because the Video BIOS doesn't support the
0040 video mode you want to use. This can be especially painful with
0041 widescreen panels, where native video modes don't have the 4:3 aspect
0042 ratio, which is what most BIOS-es are limited to.
0043 - Adjusting the refresh rate is only possible with a VBE 3.0 compliant
0044 Video BIOS. Note that many nVidia Video BIOS-es claim to be VBE 3.0
0045 compliant, while they simply ignore any refresh rate settings.
0046
0047 3. Configuration
0048 ----------------
0049
0050 uvesafb can be compiled either as a module, or directly into the kernel.
0051 In both cases it supports the same set of configuration options, which
0052 are either given on the kernel command line or as module parameters, e.g.::
0053
0054 video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
0055
0056 # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap (module)
0057
0058 Accepted options:
0059
0060 ======= =========================================================
0061 ypan Enable display panning using the VESA protected mode
0062 interface. The visible screen is just a window of the
0063 video memory, console scrolling is done by changing the
0064 start of the window. This option is available on x86
0065 only and is the default option on that architecture.
0066
0067 ywrap Same as ypan, but assumes your gfx board can wrap-around
0068 the video memory (i.e. starts reading from top if it
0069 reaches the end of video memory). Faster than ypan.
0070 Available on x86 only.
0071
0072 redraw Scroll by redrawing the affected part of the screen, this
0073 is the default on non-x86.
0074 ======= =========================================================
0075
0076 (If you're using uvesafb as a module, the above three options are
0077 used a parameter of the scroll option, e.g. scroll=ypan.)
0078
0079 =========== ====================================================================
0080 vgapal Use the standard VGA registers for palette changes.
0081
0082 pmipal Use the protected mode interface for palette changes.
0083 This is the default if the protected mode interface is
0084 available. Available on x86 only.
0085
0086 mtrr:n Setup memory type range registers for the framebuffer
0087 where n:
0088
0089 - 0 - disabled (equivalent to nomtrr)
0090 - 3 - write-combining (default)
0091
0092 Values other than 0 and 3 will result in a warning and will be
0093 treated just like 3.
0094
0095 nomtrr Do not use memory type range registers.
0096
0097 vremap:n
0098 Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
0099 according to video mode.
0100
0101 vtotal:n If the video BIOS of your card incorrectly determines the total
0102 amount of video RAM, use this option to override the BIOS (in MiB).
0103
0104 <mode> The mode you want to set, in the standard modedb format. Refer to
0105 modedb.txt for a detailed description. When uvesafb is compiled as
0106 a module, the mode string should be provided as a value of the
0107 'mode_option' option.
0108
0109 vbemode:x Force the use of VBE mode x. The mode will only be set if it's
0110 found in the VBE-provided list of supported modes.
0111 NOTE: The mode number 'x' should be specified in VESA mode number
0112 notation, not the Linux kernel one (eg. 257 instead of 769).
0113 HINT: If you use this option because normal <mode> parameter does
0114 not work for you and you use a X server, you'll probably want to
0115 set the 'nocrtc' option to ensure that the video mode is properly
0116 restored after console <-> X switches.
0117
0118 nocrtc Do not use CRTC timings while setting the video mode. This option
0119 has any effect only if the Video BIOS is VBE 3.0 compliant. Use it
0120 if you have problems with modes set the standard way. Note that
0121 using this option implies that any refresh rate adjustments will
0122 be ignored and the refresh rate will stay at your BIOS default
0123 (60 Hz).
0124
0125 noedid Do not try to fetch and use EDID-provided modes.
0126
0127 noblank Disable hardware blanking.
0128
0129 v86d:path Set path to the v86d executable. This option is only available as
0130 a module parameter, and not as a part of the video= string. If you
0131 need to use it and have uvesafb built into the kernel, use
0132 uvesafb.v86d="path".
0133 =========== ====================================================================
0134
0135 Additionally, the following parameters may be provided. They all override the
0136 EDID-provided values and BIOS defaults. Refer to your monitor's specs to get
0137 the correct values for maxhf, maxvf and maxclk for your hardware.
0138
0139 =========== ======================================
0140 maxhf:n Maximum horizontal frequency (in kHz).
0141 maxvf:n Maximum vertical frequency (in Hz).
0142 maxclk:n Maximum pixel clock (in MHz).
0143 =========== ======================================
0144
0145 4. The sysfs interface
0146 ----------------------
0147
0148 uvesafb provides several sysfs nodes for configurable parameters and
0149 additional information.
0150
0151 Driver attributes:
0152
0153 /sys/bus/platform/drivers/uvesafb
0154 v86d
0155 (default: /sbin/v86d)
0156
0157 Path to the v86d executable. v86d is started by uvesafb
0158 if an instance of the daemon isn't already running.
0159
0160 Device attributes:
0161
0162 /sys/bus/platform/drivers/uvesafb/uvesafb.0
0163 nocrtc
0164 Use the default refresh rate (60 Hz) if set to 1.
0165
0166 oem_product_name, oem_product_rev, oem_string, oem_vendor
0167 Information about the card and its maker.
0168
0169 vbe_modes
0170 A list of video modes supported by the Video BIOS along with their
0171 VBE mode numbers in hex.
0172
0173 vbe_version
0174 A BCD value indicating the implemented VBE standard.
0175
0176 5. Miscellaneous
0177 ----------------
0178
0179 Uvesafb will set a video mode with the default refresh rate and timings
0180 from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
0181
0182
0183
0184 Michal Januszewski <spock@gentoo.org>
0185
0186 Last updated: 2017-10-10
0187
0188 Documentation of the uvesafb options is loosely based on vesafb.txt.
