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diff --git a/Documentation/fb/api.txt b/Documentation/fb/api.txt deleted file mode 100644 index d52cf1e3b975..000000000000 --- a/Documentation/fb/api.txt +++ /dev/null @@ -1,306 +0,0 @@ - The Frame Buffer Device API - --------------------------- - -Last revised: June 21, 2011 - - -0. Introduction ---------------- - -This document describes the frame buffer API used by applications to interact -with frame buffer devices. In-kernel APIs between device drivers and the frame -buffer core are not described. - -Due to a lack of documentation in the original frame buffer API, drivers -behaviours differ in subtle (and not so subtle) ways. This document describes -the recommended API implementation, but applications should be prepared to -deal with different behaviours. - - -1. Capabilities ---------------- - -Device and driver capabilities are reported in the fixed screen information -capabilities field. - -struct fb_fix_screeninfo { - ... - __u16 capabilities; /* see FB_CAP_* */ - ... -}; - -Application should use those capabilities to find out what features they can -expect from the device and driver. - -- FB_CAP_FOURCC - -The driver supports the four character code (FOURCC) based format setting API. -When supported, formats are configured using a FOURCC instead of manually -specifying color components layout. - - -2. Types and visuals --------------------- - -Pixels are stored in memory in hardware-dependent formats. Applications need -to be aware of the pixel storage format in order to write image data to the -frame buffer memory in the format expected by the hardware. - -Formats are described by frame buffer types and visuals. Some visuals require -additional information, which are stored in the variable screen information -bits_per_pixel, grayscale, red, green, blue and transp fields. - -Visuals describe how color information is encoded and assembled to create -macropixels. Types describe how macropixels are stored in memory. The following -types and visuals are supported. - -- FB_TYPE_PACKED_PIXELS - -Macropixels are stored contiguously in a single plane. If the number of bits -per macropixel is not a multiple of 8, whether macropixels are padded to the -next multiple of 8 bits or packed together into bytes depends on the visual. - -Padding at end of lines may be present and is then reported through the fixed -screen information line_length field. - -- FB_TYPE_PLANES - -Macropixels are split across multiple planes. The number of planes is equal to -the number of bits per macropixel, with plane i'th storing i'th bit from all -macropixels. - -Planes are located contiguously in memory. - -- FB_TYPE_INTERLEAVED_PLANES - -Macropixels are split across multiple planes. The number of planes is equal to -the number of bits per macropixel, with plane i'th storing i'th bit from all -macropixels. - -Planes are interleaved in memory. The interleave factor, defined as the -distance in bytes between the beginning of two consecutive interleaved blocks -belonging to different planes, is stored in the fixed screen information -type_aux field. - -- FB_TYPE_FOURCC - -Macropixels are stored in memory as described by the format FOURCC identifier -stored in the variable screen information grayscale field. - -- FB_VISUAL_MONO01 - -Pixels are black or white and stored on a number of bits (typically one) -specified by the variable screen information bpp field. - -Black pixels are represented by all bits set to 1 and white pixels by all bits -set to 0. When the number of bits per pixel is smaller than 8, several pixels -are packed together in a byte. - -FB_VISUAL_MONO01 is currently used with FB_TYPE_PACKED_PIXELS only. - -- FB_VISUAL_MONO10 - -Pixels are black or white and stored on a number of bits (typically one) -specified by the variable screen information bpp field. - -Black pixels are represented by all bits set to 0 and white pixels by all bits -set to 1. When the number of bits per pixel is smaller than 8, several pixels -are packed together in a byte. - -FB_VISUAL_MONO01 is currently used with FB_TYPE_PACKED_PIXELS only. - -- FB_VISUAL_TRUECOLOR - -Pixels are broken into red, green and blue components, and each component -indexes a read-only lookup table for the corresponding value. Lookup tables -are device-dependent, and provide linear or non-linear ramps. - -Each component is stored in a macropixel according to the variable screen -information red, green, blue and transp fields. - -- FB_VISUAL_PSEUDOCOLOR and FB_VISUAL_STATIC_PSEUDOCOLOR - -Pixel values are encoded as indices into a colormap that stores red, green and -blue components. The colormap is read-only for FB_VISUAL_STATIC_PSEUDOCOLOR -and read-write for FB_VISUAL_PSEUDOCOLOR. - -Each pixel value is stored in the number of bits reported by the variable -screen information bits_per_pixel field. - -- FB_VISUAL_DIRECTCOLOR - -Pixels are broken into red, green and blue components, and each component -indexes a programmable lookup table for the corresponding value. - -Each component is stored in a macropixel according to the variable screen -information red, green, blue and transp fields. - -- FB_VISUAL_FOURCC - -Pixels are encoded and interpreted as described by the format FOURCC -identifier stored in the variable screen information grayscale field. - - -3. Screen information ---------------------- - -Screen information are queried by applications using the FBIOGET_FSCREENINFO -and FBIOGET_VSCREENINFO ioctls. Those ioctls take a pointer to a -fb_fix_screeninfo and fb_var_screeninfo structure respectively. - -struct fb_fix_screeninfo stores device independent unchangeable information -about the frame buffer device and the current format. Those information can't -be directly modified by applications, but can be changed by the driver when an -application modifies the format. - -struct fb_fix_screeninfo { - char id[16]; /* identification string eg "TT Builtin" */ - unsigned long smem_start; /* Start of frame buffer mem */ - /* (physical address) */ - __u32 smem_len; /* Length of frame buffer mem */ - __u32 type; /* see FB_TYPE_* */ - __u32 type_aux; /* Interleave for interleaved Planes */ - __u32 visual; /* see FB_VISUAL_* */ - __u16 xpanstep; /* zero if no hardware panning */ - __u16 ypanstep; /* zero if no hardware panning */ - __u16 ywrapstep; /* zero if no hardware ywrap */ - __u32 line_length; /* length of a line in bytes */ - unsigned long mmio_start; /* Start of Memory Mapped I/O */ - /* (physical address) */ - __u32 mmio_len; /* Length of Memory Mapped I/O */ - __u32 accel; /* Indicate to driver which */ - /* specific chip/card we have */ - __u16 capabilities; /* see FB_CAP_* */ - __u16 reserved[2]; /* Reserved for future compatibility */ -}; - -struct fb_var_screeninfo stores device independent changeable information -about a frame buffer device, its current format and video mode, as well as -other miscellaneous parameters. - -struct fb_var_screeninfo { - __u32 xres; /* visible resolution */ - __u32 yres; - __u32 xres_virtual; /* virtual resolution */ - __u32 yres_virtual; - __u32 xoffset; /* offset from virtual to visible */ - __u32 yoffset; /* resolution */ - - __u32 bits_per_pixel; /* guess what */ - __u32 grayscale; /* 0 = color, 1 = grayscale, */ - /* >1 = FOURCC */ - struct fb_bitfield red; /* bitfield in fb mem if true color, */ - struct fb_bitfield green; /* else only length is significant */ - struct fb_bitfield blue; - struct fb_bitfield transp; /* transparency */ - - __u32 nonstd; /* != 0 Non standard pixel format */ - - __u32 activate; /* see FB_ACTIVATE_* */ - - __u32 height; /* height of picture in mm */ - __u32 width; /* width of picture in mm */ - - __u32 accel_flags; /* (OBSOLETE) see fb_info.flags */ - - /* Timing: All values in pixclocks, except pixclock (of course) */ - __u32 pixclock; /* pixel clock in ps (pico seconds) */ - __u32 left_margin; /* time from sync to picture */ - __u32 right_margin; /* time from picture to sync */ - __u32 upper_margin; /* time from sync to picture */ - __u32 lower_margin; - __u32 hsync_len; /* length of horizontal sync */ - __u32 vsync_len; /* length of vertical sync */ - __u32 sync; /* see FB_SYNC_* */ - __u32 vmode; /* see FB_VMODE_* */ - __u32 rotate; /* angle we rotate counter clockwise */ - __u32 colorspace; /* colorspace for FOURCC-based modes */ - __u32 reserved[4]; /* Reserved for future compatibility */ -}; - -To modify variable information, applications call the FBIOPUT_VSCREENINFO -ioctl with a pointer to a fb_var_screeninfo structure. If the call is -successful, the driver will update the fixed screen information accordingly. - -Instead of filling the complete fb_var_screeninfo structure manually, -applications should call the FBIOGET_VSCREENINFO ioctl and modify only the -fields they care about. - - -4. Format configuration ------------------------ - -Frame buffer devices offer two ways to configure the frame buffer format: the -legacy API and the FOURCC-based API. - - -The legacy API has been the only frame buffer format configuration API for a -long time and is thus widely used by application. It is the recommended API -for applications when using RGB and grayscale formats, as well as legacy -non-standard formats. - -To select a format, applications set the fb_var_screeninfo bits_per_pixel field -to the desired frame buffer depth. Values up to 8 will usually map to -monochrome, grayscale or pseudocolor visuals, although this is not required. - -- For grayscale formats, applications set the grayscale field to one. The red, - blue, green and transp fields must be set to 0 by applications and ignored by - drivers. Drivers must fill the red, blue and green offsets to 0 and lengths - to the bits_per_pixel value. - -- For pseudocolor formats, applications set the grayscale field to zero. The - red, blue, green and transp fields must be set to 0 by applications and - ignored by drivers. Drivers must fill the red, blue and green offsets to 0 - and lengths to the bits_per_pixel value. - -- For truecolor and directcolor formats, applications set the grayscale field - to zero, and the red, blue, green and transp fields to describe the layout of - color components in memory. - -struct fb_bitfield { - __u32 offset; /* beginning of bitfield */ - __u32 length; /* length of bitfield */ - __u32 msb_right; /* != 0 : Most significant bit is */ - /* right */ -}; - - Pixel values are bits_per_pixel wide and are split in non-overlapping red, - green, blue and alpha (transparency) components. Location and size of each - component in the pixel value are described by the fb_bitfield offset and - length fields. Offset are computed from the right. - - Pixels are always stored in an integer number of bytes. If the number of - bits per pixel is not a multiple of 8, pixel values are padded to the next - multiple of 8 bits. - -Upon successful format configuration, drivers update the fb_fix_screeninfo -type, visual and line_length fields depending on the selected format. - - -The FOURCC-based API replaces format descriptions by four character codes -(FOURCC). FOURCCs are abstract identifiers that uniquely define a format -without explicitly describing it. This is the only API that supports YUV -formats. Drivers are also encouraged to implement the FOURCC-based API for RGB -and grayscale formats. - -Drivers that support the FOURCC-based API report this capability by setting -the FB_CAP_FOURCC bit in the fb_fix_screeninfo capabilities field. - -FOURCC definitions are located in the linux/videodev2.h header. However, and -despite starting with the V4L2_PIX_FMT_prefix, they are not restricted to V4L2 -and don't require usage of the V4L2 subsystem. FOURCC documentation is -available in Documentation/media/uapi/v4l/pixfmt.rst. - -To select a format, applications set the grayscale field to the desired FOURCC. -For YUV formats, they should also select the appropriate colorspace by setting -the colorspace field to one of the colorspaces listed in linux/videodev2.h and -documented in Documentation/media/uapi/v4l/colorspaces.rst. - -The red, green, blue and transp fields are not used with the FOURCC-based API. -For forward compatibility reasons applications must zero those fields, and -drivers must ignore them. Values other than 0 may get a meaning in future -extensions. - -Upon successful format configuration, drivers update the fb_fix_screeninfo -type, visual and line_length fields depending on the selected format. The type -and visual fields are set to FB_TYPE_FOURCC and FB_VISUAL_FOURCC respectively. |