android_kernel_xiaomi_sm8350/Documentation/fb/pxafb.txt
Eric Miao 198fc108ee [ARM] pxafb: add support for overlay1 and overlay2 as framebuffer devices
PXA27x and later processors support overlay1 and overlay2 on-top of the
base framebuffer (although under-neath the base is also possible). They
support palette and no-palette RGB formats, as well as YUV formats (only
available on overlay2). These overlays have dedicated DMA channels and
behave in a similar way as a framebuffer.

This heavily simplified and re-structured work is based on the original
pxafb_overlay.c (which is pending for mainline merge for a long time).

The major problems with this pxafb_overlay.c are (if you are interested
in the history):

  1. heavily redundant (the control logics for overlay1 and overlay2 are
     actually identical except for some small operations,  which are now
     abstracted into a 'pxafb_layer_ops' structure)

  2. a lot of useless and un-tested code (two workarounds which are now
     fixed on mature silicons)

  3. cursorfb is actually useless, hardware cursor should not be used
     this way, and the code was actually un-tested for a long time.

The code in this patch should be self-explanatory, I tried to add minimum
comments. As said, this is basically simplified, there are several things
still on the pending list:

  1. palette mode is un-supported and un-tested (although re-using the
     palette code of the base framebuffer is actually very easy now with
     previous clean-up patches)

  2. fb_pan_display for overlay(s) is un-supported

  3. the base framebuffer can actually be abstracted by 'pxafb_layer' as
     well, which will help further re-use of the code and keep a better
     and consistent structure. (This is the reason I named it 'pxafb_layer'
     instead of 'pxafb_overlay' or something alike)

See Documentation/fb/pxafb.txt for additional usage information.

Signed-off-by: Eric Miao <eric.miao@marvell.com>
Cc: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Eric Miao <ycmiao@ycmiao-hp520.(none)>
2008-12-29 18:00:04 +08:00

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