About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / fb / uvesafb.txt




Custom Search

Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

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.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.