Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) =============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) Frame Buffer device internals
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) =============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) This is a first start for some documentation about frame buffer device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6) internals.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8) Authors:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) - Geert Uytterhoeven <geert@linux-m68k.org>, 21 July 1998
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) - James Simmons <jsimmons@user.sf.net>, Nov 26 2002
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) --------------------------------------------------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) Structures used by the frame buffer device API
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) ==============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) The following structures play a role in the game of frame buffer devices. They
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) are defined in <linux/fb.h>.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) 1. Outside the kernel (user space)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23)   - struct fb_fix_screeninfo
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25)     Device independent unchangeable information about a frame buffer device and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)     a specific video mode. This can be obtained using the FBIOGET_FSCREENINFO
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27)     ioctl.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29)   - struct fb_var_screeninfo
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31)     Device independent changeable information about a frame buffer device and a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32)     specific video mode. This can be obtained using the FBIOGET_VSCREENINFO
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33)     ioctl, and updated with the FBIOPUT_VSCREENINFO ioctl. If you want to pan
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)     the screen only, you can use the FBIOPAN_DISPLAY ioctl.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36)   - struct fb_cmap
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38)     Device independent colormap information. You can get and set the colormap
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39)     using the FBIOGETCMAP and FBIOPUTCMAP ioctls.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) 2. Inside the kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44)   - struct fb_info
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46)     Generic information, API and low level information about a specific frame
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47)     buffer device instance (slot number, board address, ...).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49)   - struct `par`
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51)     Device dependent information that uniquely defines the video mode for this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52)     particular piece of hardware.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) Visuals used by the frame buffer device API
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) ===========================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) Monochrome (FB_VISUAL_MONO01 and FB_VISUAL_MONO10)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) --------------------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) Each pixel is either black or white.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) Pseudo color (FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) ---------------------------------------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) The whole pixel value is fed through a programmable lookup table that has one
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) color (including red, green, and blue intensities) for each possible pixel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) value, and that color is displayed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) True color (FB_VISUAL_TRUECOLOR)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) --------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) The pixel value is broken up into red, green, and blue fields.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) Direct color (FB_VISUAL_DIRECTCOLOR)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) ------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) The pixel value is broken up into red, green, and blue fields, each of which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) are looked up in separate red, green, and blue lookup tables.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) Grayscale displays
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) ------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) Grayscale and static grayscale are special variants of pseudo color and static
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) pseudo color, where the red, green and blue components are always equal to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) each other.