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1
2 uvesafb - A Generic Driver for VBE2+ compliant video cards
3 ==========================================================
4
5 1. Requirements
6 ---------------
7
8 uvesafb should work with any video card that has a Video BIOS compliant
9 with the VBE 2.0 standard.
10
11 Unlike other drivers, uvesafb makes use of a userspace helper called
12 v86d. v86d is used to run the x86 Video BIOS code in a simulated and
13 controlled environment. This allows uvesafb to function on arches other
14 than x86. Check the v86d documentation for a list of currently supported
15 arches.
16
17 v86d source code can be downloaded from the following website:
18 http://dev.gentoo.org/~spock/projects/uvesafb
19
20 Please refer to the v86d documentation for detailed configuration and
21 installation instructions.
22
23 Note that the v86d userspace helper has to be available at all times in
24 order for uvesafb to work properly. If you want to use uvesafb during
25 early boot, you will have to include v86d into an initramfs image, and
26 either compile it into the kernel or use it as an initrd.
27
28 2. Caveats and limitations
29 --------------------------
30
31 uvesafb is a _generic_ driver which supports a wide variety of video
32 cards, but which is ultimately limited by the Video BIOS interface.
33 The most important limitations are:
34
35 - Lack of any type of acceleration.
36 - A strict and limited set of supported video modes. Often the native
37 or most optimal resolution/refresh rate for your setup will not work
38 with uvesafb, simply because the Video BIOS doesn't support the
39 video mode you want to use. This can be especially painful with
40 widescreen panels, where native video modes don't have the 4:3 aspect
41 ratio, which is what most BIOS-es are limited to.
42 - Adjusting the refresh rate is only possible with a VBE 3.0 compliant
43 Video BIOS. Note that many nVidia Video BIOS-es claim to be VBE 3.0
44 compliant, while they simply ignore any refresh rate settings.
45
46 3. Configuration
47 ----------------
48
49 uvesafb can be compiled either as a module, or directly into the kernel.
50 In both cases it supports the same set of configuration options, which
51 are either given on the kernel command line or as module parameters, e.g.:
52
53 video=uvesafb:1024x768-32,mtrr:3,ywrap (compiled into the kernel)
54
55 # modprobe uvesafb mode_option=1024x768-32 mtrr=3 scroll=ywrap (module)
56
57 Accepted options:
58
59 ypan Enable display panning using the VESA protected mode
60 interface. The visible screen is just a window of the
61 video memory, console scrolling is done by changing the
62 start of the window. This option is available on x86
63 only and is the default option on that architecture.
64
65 ywrap Same as ypan, but assumes your gfx board can wrap-around
66 the video memory (i.e. starts reading from top if it
67 reaches the end of video memory). Faster than ypan.
68 Available on x86 only.
69
70 redraw Scroll by redrawing the affected part of the screen, this
71 is the default on non-x86.
72
73 (If you're using uvesafb as a module, the above three options are
74 used a parameter of the scroll option, e.g. scroll=ypan.)
75
76 vgapal Use the standard VGA registers for palette changes.
77
78 pmipal Use the protected mode interface for palette changes.
79 This is the default if the protected mode interface is
80 available. Available on x86 only.
81
82 mtrr:n Setup memory type range registers for the framebuffer
83 where n:
84 0 - disabled (equivalent to nomtrr)
85 3 - write-combining (default)
86
87 Values other than 0 and 3 will result in a warning and will be
88 treated just like 3.
89
90 nomtrr Do not use memory type range registers.
91
92 vremap:n
93 Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
94 according to video mode.
95
96 vtotal:n
97 If the video BIOS of your card incorrectly determines the total
98 amount of video RAM, use this option to override the BIOS (in MiB).
99
100 <mode> The mode you want to set, in the standard modedb format. Refer to
101 modedb.txt for a detailed description. When uvesafb is compiled as
102 a module, the mode string should be provided as a value of the
103 'mode_option' option.
104
105 vbemode:x
106 Force the use of VBE mode x. The mode will only be set if it's
107 found in the VBE-provided list of supported modes.
108 NOTE: The mode number 'x' should be specified in VESA mode number
109 notation, not the Linux kernel one (eg. 257 instead of 769).
110 HINT: If you use this option because normal <mode> parameter does
111 not work for you and you use a X server, you'll probably want to
112 set the 'nocrtc' option to ensure that the video mode is properly
113 restored after console <-> X switches.
114
115 nocrtc Do not use CRTC timings while setting the video mode. This option
116 has any effect only if the Video BIOS is VBE 3.0 compliant. Use it
117 if you have problems with modes set the standard way. Note that
118 using this option implies that any refresh rate adjustments will
119 be ignored and the refresh rate will stay at your BIOS default (60 Hz).
120
121 noedid Do not try to fetch and use EDID-provided modes.
122
123 noblank Disable hardware blanking.
124
125 v86d:path
126 Set path to the v86d executable. This option is only available as
127 a module parameter, and not as a part of the video= string. If you
128 need to use it and have uvesafb built into the kernel, use
129 uvesafb.v86d="path".
130
131 Additionally, the following parameters may be provided. They all override the
132 EDID-provided values and BIOS defaults. Refer to your monitor's specs to get
133 the correct values for maxhf, maxvf and maxclk for your hardware.
134
135 maxhf:n Maximum horizontal frequency (in kHz).
136 maxvf:n Maximum vertical frequency (in Hz).
137 maxclk:n Maximum pixel clock (in MHz).
138
139 4. The sysfs interface
140 ----------------------
141
142 uvesafb provides several sysfs nodes for configurable parameters and
143 additional information.
144
145 Driver attributes:
146
147 /sys/bus/platform/drivers/uvesafb
148 - v86d (default: /sbin/v86d)
149 Path to the v86d executable. v86d is started by uvesafb
150 if an instance of the daemon isn't already running.
151
152 Device attributes:
153
154 /sys/bus/platform/drivers/uvesafb/uvesafb.0
155 - nocrtc
156 Use the default refresh rate (60 Hz) if set to 1.
157
158 - oem_product_name
159 - oem_product_rev
160 - oem_string
161 - oem_vendor
162 Information about the card and its maker.
163
164 - vbe_modes
165 A list of video modes supported by the Video BIOS along with their
166 VBE mode numbers in hex.
167
168 - vbe_version
169 A BCD value indicating the implemented VBE standard.
170
171 5. Miscellaneous
172 ----------------
173
174 Uvesafb will set a video mode with the default refresh rate and timings
175 from the Video BIOS if you set pixclock to 0 in fb_var_screeninfo.
176
177
178 --
179 Michal Januszewski <spock@gentoo.org>
180 Last updated: 2009-03-30
181
182 Documentation of the uvesafb options is loosely based on vesafb.txt.
183