From patchwork Wed Aug 31 11:18:19 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Laurent Pinchart X-Patchwork-Id: 1115642 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by demeter2.kernel.org (8.14.4/8.14.4) with ESMTP id p7VBI2Al019671 for ; Wed, 31 Aug 2011 11:18:02 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754561Ab1HaLR4 (ORCPT ); Wed, 31 Aug 2011 07:17:56 -0400 Received: from perceval.ideasonboard.com ([95.142.166.194]:60203 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752824Ab1HaLRy (ORCPT ); Wed, 31 Aug 2011 07:17:54 -0400 Received: from localhost.localdomain (unknown [91.178.27.34]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 408E435AA3; Wed, 31 Aug 2011 11:17:53 +0000 (UTC) From: Laurent Pinchart To: linux-fbdev@vger.kernel.org Cc: linux-media@vger.kernel.org, magnus.damm@gmail.com Subject: [PATCH v3 1/3] fbdev: Add FOURCC-based format configuration API Date: Wed, 31 Aug 2011 13:18:19 +0200 Message-Id: <1314789501-824-2-git-send-email-laurent.pinchart@ideasonboard.com> X-Mailer: git-send-email 1.7.3.4 In-Reply-To: <1314789501-824-1-git-send-email-laurent.pinchart@ideasonboard.com> References: <1314789501-824-1-git-send-email-laurent.pinchart@ideasonboard.com> Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.6 (demeter2.kernel.org [140.211.167.43]); Wed, 31 Aug 2011 11:18:02 +0000 (UTC) This API will be used to support YUV frame buffer formats in a standard way. Last but not least, create a much needed fbdev API documentation and document the format setting APIs. Signed-off-by: Laurent Pinchart --- Documentation/fb/api.txt | 317 ++++++++++++++++++++++++++++++++++++++++++++++ include/linux/fb.h | 28 +++- 2 files changed, 339 insertions(+), 6 deletions(-) create mode 100644 Documentation/fb/api.txt diff --git a/Documentation/fb/api.txt b/Documentation/fb/api.txt new file mode 100644 index 0000000..d842534 --- /dev/null +++ b/Documentation/fb/api.txt @@ -0,0 +1,317 @@ + 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, fourcc, 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 fourcc 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 fourcc 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 */ + union { + struct { /* Legacy format API */ + __u32 grayscale; /* 0 = color, 1 = grayscale */ + /* bitfields in fb mem if true color, else only */ + /* length is significant */ + struct fb_bitfield red; + struct fb_bitfield green; + struct fb_bitfield blue; + struct fb_bitfield transp; /* transparency */ + }; + struct { /* FOURCC-based format API */ + __u32 fourcc; /* FOURCC format */ + __u32 colorspace; + __u32 reserved[11]; + } fourcc; + }; + + __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 reserved[5]; /* 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/DocBook/v4l/pixfmt.xml. + +To select a format, applications set the fourcc.fourcc field to the desired +FOURCC. For YUV formats, they should also select the appropriate colorspace by +setting the fourcc.colorspace field to one of the colorspaces listed in +linux/videodev2.h and documented in Documentation/DocBook/v4l/colorspaces.xml. + +For forward compatibility reasons applications must zero the fourcc reserved +fields by zeroing the whole fourcc structure before filling it. The reserved +fields must be ignored by drivers. Values other than 0 may get a meaning in +future extensions. Note that the grayscale, red, green, blue and transp field +share memory with the fourcc field. Application must thus not touch those +fields when using the FOURCC-based API. + +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. diff --git a/include/linux/fb.h b/include/linux/fb.h index 1d6836c..98b23e3 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -45,6 +45,7 @@ #define FB_TYPE_INTERLEAVED_PLANES 2 /* Interleaved planes */ #define FB_TYPE_TEXT 3 /* Text/attributes */ #define FB_TYPE_VGA_PLANES 4 /* EGA/VGA planes */ +#define FB_TYPE_FOURCC 5 /* Type identified by a V4L2 FOURCC */ #define FB_AUX_TEXT_MDA 0 /* Monochrome text */ #define FB_AUX_TEXT_CGA 1 /* CGA/EGA/VGA Color text */ @@ -69,6 +70,7 @@ #define FB_VISUAL_PSEUDOCOLOR 3 /* Pseudo color (like atari) */ #define FB_VISUAL_DIRECTCOLOR 4 /* Direct color */ #define FB_VISUAL_STATIC_PSEUDOCOLOR 5 /* Pseudo color readonly */ +#define FB_VISUAL_FOURCC 6 /* Visual identified by a V4L2 FOURCC */ #define FB_ACCEL_NONE 0 /* no hardware accelerator */ #define FB_ACCEL_ATARIBLITT 1 /* Atari Blitter */ @@ -154,6 +156,8 @@ #define FB_ACCEL_PUV3_UNIGFX 0xa0 /* PKUnity-v3 Unigfx */ +#define FB_CAP_FOURCC 1 /* Device supports FOURCC-based formats */ + struct fb_fix_screeninfo { char id[16]; /* identification string eg "TT Builtin" */ unsigned long smem_start; /* Start of frame buffer mem */ @@ -171,7 +175,8 @@ struct fb_fix_screeninfo { __u32 mmio_len; /* Length of Memory Mapped I/O */ __u32 accel; /* Indicate to driver which */ /* specific chip/card we have */ - __u16 reserved[3]; /* Reserved for future compatibility */ + __u16 capabilities; /* see FB_CAP_* */ + __u16 reserved[2]; /* Reserved for future compatibility */ }; /* Interpretation of offset for color fields: All offsets are from the right, @@ -246,12 +251,23 @@ struct fb_var_screeninfo { __u32 yoffset; /* resolution */ __u32 bits_per_pixel; /* guess what */ - __u32 grayscale; /* != 0 Graylevels instead of colors */ - 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 */ + union { + struct { /* Legacy format API */ + __u32 grayscale; /* 0 = color, 1 = grayscale */ + /* bitfields in fb mem if true color, else only */ + /* length is significant */ + struct fb_bitfield red; + struct fb_bitfield green; + struct fb_bitfield blue; + struct fb_bitfield transp; /* transparency */ + }; + struct { /* FOURCC-based format API */ + __u32 fourcc; /* FOURCC format */ + __u32 colorspace; + __u32 reserved[11]; + } fourcc; + }; __u32 nonstd; /* != 0 Non standard pixel format */