Root/Documentation/fb/pxafb.txt

1Driver for PXA25x LCD controller
2================================
3
4The driver supports the following options, either via
5options=<OPTIONS> when modular or video=pxafb:<OPTIONS> when built in.
6
7For example:
8    modprobe pxafb options=vmem:2M,mode:640x480-8,passive
9or on the kernel command line
10    video=pxafb:vmem:2M,mode:640x480-8,passive
11
12vmem: VIDEO_MEM_SIZE
13    Amount of video memory to allocate (can be suffixed with K or M
14    for kilobytes or megabytes)
15
16mode:XRESxYRES[-BPP]
17    XRES == LCCR1_PPL + 1
18    YRES == LLCR2_LPP + 1
19        The resolution of the display in pixels
20    BPP == The bit depth. Valid values are 1, 2, 4, 8 and 16.
21
22pixclock:PIXCLOCK
23    Pixel clock in picoseconds
24
25left:LEFT == LCCR1_BLW + 1
26right:RIGHT == LCCR1_ELW + 1
27hsynclen:HSYNC == LCCR1_HSW + 1
28upper:UPPER == LCCR2_BFW
29lower:LOWER == LCCR2_EFR
30vsynclen:VSYNC == LCCR2_VSW + 1
31    Display margins and sync times
32
33color | mono => LCCR0_CMS
34    umm...
35
36active | passive => LCCR0_PAS
37    Active (TFT) or Passive (STN) display
38
39single | dual => LCCR0_SDS
40    Single or dual panel passive display
41
424pix | 8pix => LCCR0_DPD
43    4 or 8 pixel monochrome single panel data
44
45hsync:HSYNC
46vsync:VSYNC
47    Horizontal and vertical sync. 0 => active low, 1 => active
48    high.
49
50dpc:DPC
51    Double pixel clock. 1=>true, 0=>false
52
53outputen:POLARITY
54    Output Enable Polarity. 0 => active low, 1 => active high
55
56pixclockpol:POLARITY
57    pixel clock polarity
58    0 => falling edge, 1 => rising edge
59
60
61Overlay Support for PXA27x and later LCD controllers
62====================================================
63
64  PXA27x and later processors support overlay1 and overlay2 on-top of the
65  base framebuffer (although under-neath the base is also possible). They
66  support palette and no-palette RGB formats, as well as YUV formats (only
67  available on overlay2). These overlays have dedicated DMA channels and
68  behave in a similar way as a framebuffer.
69
70  However, there are some differences between these overlay framebuffers
71  and normal framebuffers, as listed below:
72
73  1. overlay can start at a 32-bit word aligned position within the base
74     framebuffer, which means they have a start (x, y). This information
75     is encoded into var->nonstd (no, var->xoffset and var->yoffset are
76     not for such purpose).
77
78  2. overlay framebuffer is allocated dynamically according to specified
79     'struct fb_var_screeninfo', the amount is decided by:
80
81        var->xres_virtual * var->yres_virtual * bpp
82
83     bpp = 16 -- for RGB565 or RGBT555
84         = 24 -- for YUV444 packed
85         = 24 -- for YUV444 planar
86     = 16 -- for YUV422 planar (1 pixel = 1 Y + 1/2 Cb + 1/2 Cr)
87     = 12 -- for YUV420 planar (1 pixel = 1 Y + 1/4 Cb + 1/4 Cr)
88
89     NOTE:
90
91     a. overlay does not support panning in x-direction, thus
92        var->xres_virtual will always be equal to var->xres
93
94     b. line length of overlay(s) must be on a 32-bit word boundary,
95        for YUV planar modes, it is a requirement for the component
96    with minimum bits per pixel, e.g. for YUV420, Cr component
97    for one pixel is actually 2-bits, it means the line length
98    should be a multiple of 16-pixels
99
100     c. starting horizontal position (XPOS) should start on a 32-bit
101        word boundary, otherwise the fb_check_var() will just fail.
102
103     d. the rectangle of the overlay should be within the base plane,
104        otherwise fail
105
106     Applications should follow the sequence below to operate an overlay
107     framebuffer:
108
109         a. open("/dev/fb[1-2]", ...)
110     b. ioctl(fd, FBIOGET_VSCREENINFO, ...)
111     c. modify 'var' with desired parameters:
112        1) var->xres and var->yres
113        2) larger var->yres_virtual if more memory is required,
114           usually for double-buffering
115        3) var->nonstd for starting (x, y) and color format
116        4) var->{red, green, blue, transp} if RGB mode is to be used
117     d. ioctl(fd, FBIOPUT_VSCREENINFO, ...)
118     e. ioctl(fd, FBIOGET_FSCREENINFO, ...)
119     f. mmap
120     g. ...
121
122  3. for YUV planar formats, these are actually not supported within the
123     framebuffer framework, application has to take care of the offsets
124     and lengths of each component within the framebuffer.
125
126  4. var->nonstd is used to pass starting (x, y) position and color format,
127     the detailed bit fields are shown below:
128
129    31 23 20 10 0
130     +-----------------+---+----------+----------+
131     | ... unused ... |FOR| XPOS | YPOS |
132     +-----------------+---+----------+----------+
133
134     FOR - color format, as defined by OVERLAY_FORMAT_* in pxafb.h
135            0 - RGB
136        1 - YUV444 PACKED
137        2 - YUV444 PLANAR
138        3 - YUV422 PLANAR
139        4 - YUR420 PLANAR
140
141     XPOS - starting horizontal position
142     YPOS - starting vertical position
143

Archive Download this file



interactive