174 lines
4.6 KiB
ReStructuredText
174 lines
4.6 KiB
ReStructuredText
================================
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Driver for PXA25x LCD controller
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================================
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The driver supports the following options, either via
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options=<OPTIONS> when modular or video=pxafb:<OPTIONS> when built in.
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For example::
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modprobe pxafb options=vmem:2M,mode:640x480-8,passive
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or on the kernel command line::
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video=pxafb:vmem:2M,mode:640x480-8,passive
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vmem: VIDEO_MEM_SIZE
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Amount of video memory to allocate (can be suffixed with K or M
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for kilobytes or megabytes)
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mode:XRESxYRES[-BPP]
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XRES == LCCR1_PPL + 1
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YRES == LLCR2_LPP + 1
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The resolution of the display in pixels
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BPP == The bit depth. Valid values are 1, 2, 4, 8 and 16.
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pixclock:PIXCLOCK
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Pixel clock in picoseconds
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left:LEFT == LCCR1_BLW + 1
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right:RIGHT == LCCR1_ELW + 1
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hsynclen:HSYNC == LCCR1_HSW + 1
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upper:UPPER == LCCR2_BFW
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lower:LOWER == LCCR2_EFR
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vsynclen:VSYNC == LCCR2_VSW + 1
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Display margins and sync times
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color | mono => LCCR0_CMS
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umm...
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active | passive => LCCR0_PAS
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Active (TFT) or Passive (STN) display
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single | dual => LCCR0_SDS
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Single or dual panel passive display
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4pix | 8pix => LCCR0_DPD
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4 or 8 pixel monochrome single panel data
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hsync:HSYNC, vsync:VSYNC
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Horizontal and vertical sync. 0 => active low, 1 => active
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high.
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dpc:DPC
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Double pixel clock. 1=>true, 0=>false
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outputen:POLARITY
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Output Enable Polarity. 0 => active low, 1 => active high
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pixclockpol:POLARITY
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pixel clock polarity
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0 => falling edge, 1 => rising edge
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Overlay Support for PXA27x and later LCD controllers
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====================================================
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PXA27x and later processors support overlay1 and overlay2 on-top of the
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base framebuffer (although under-neath the base is also possible). They
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support palette and no-palette RGB formats, as well as YUV formats (only
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available on overlay2). These overlays have dedicated DMA channels and
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behave in a similar way as a framebuffer.
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However, there are some differences between these overlay framebuffers
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and normal framebuffers, as listed below:
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1. overlay can start at a 32-bit word aligned position within the base
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framebuffer, which means they have a start (x, y). This information
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is encoded into var->nonstd (no, var->xoffset and var->yoffset are
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not for such purpose).
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2. overlay framebuffer is allocated dynamically according to specified
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'struct fb_var_screeninfo', the amount is decided by::
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var->xres_virtual * var->yres_virtual * bpp
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bpp = 16 -- for RGB565 or RGBT555
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bpp = 24 -- for YUV444 packed
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bpp = 24 -- for YUV444 planar
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bpp = 16 -- for YUV422 planar (1 pixel = 1 Y + 1/2 Cb + 1/2 Cr)
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bpp = 12 -- for YUV420 planar (1 pixel = 1 Y + 1/4 Cb + 1/4 Cr)
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NOTE:
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a. overlay does not support panning in x-direction, thus
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var->xres_virtual will always be equal to var->xres
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b. line length of overlay(s) must be on a 32-bit word boundary,
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for YUV planar modes, it is a requirement for the component
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with minimum bits per pixel, e.g. for YUV420, Cr component
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for one pixel is actually 2-bits, it means the line length
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should be a multiple of 16-pixels
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c. starting horizontal position (XPOS) should start on a 32-bit
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word boundary, otherwise the fb_check_var() will just fail.
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d. the rectangle of the overlay should be within the base plane,
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otherwise fail
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Applications should follow the sequence below to operate an overlay
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framebuffer:
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a. open("/dev/fb[1-2]", ...)
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b. ioctl(fd, FBIOGET_VSCREENINFO, ...)
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c. modify 'var' with desired parameters:
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1) var->xres and var->yres
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2) larger var->yres_virtual if more memory is required,
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usually for double-buffering
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3) var->nonstd for starting (x, y) and color format
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4) var->{red, green, blue, transp} if RGB mode is to be used
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d. ioctl(fd, FBIOPUT_VSCREENINFO, ...)
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e. ioctl(fd, FBIOGET_FSCREENINFO, ...)
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f. mmap
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g. ...
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3. for YUV planar formats, these are actually not supported within the
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framebuffer framework, application has to take care of the offsets
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and lengths of each component within the framebuffer.
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4. var->nonstd is used to pass starting (x, y) position and color format,
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the detailed bit fields are shown below::
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31 23 20 10 0
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+-----------------+---+----------+----------+
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| ... unused ... |FOR| XPOS | YPOS |
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+-----------------+---+----------+----------+
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FOR - color format, as defined by OVERLAY_FORMAT_* in pxafb.h
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- 0 - RGB
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- 1 - YUV444 PACKED
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- 2 - YUV444 PLANAR
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- 3 - YUV422 PLANAR
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- 4 - YUR420 PLANAR
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XPOS - starting horizontal position
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YPOS - starting vertical position
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