【精选】Linux DRM(五) |
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【精选】Linux DRM(五)
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了解libdrm 应用层代码库
1.Graphics Framework
2.Introduction to libdrm libdrm provides a user space library for accessing the DRM, direct rendering manager, on operating systems that support the ioctl interface. libdrm is a low-level library, typically used by graphics drivers such as the Mesa DRI drivers, the X drivers, libva and similar projects. 2.1.libdrm framework DRM是Linux内核层的显示驱动框架，它把显示功能封装成 open/close/ioctl 等标准接口，用户空间的程序调用这些接口，驱动设备，显示数据。 libdrm库封装了DRM driver提供的这些接口。通过libdrm库，程序可以间接调用DRM Driver。
DRM exports API through ioctl, libdrm is a user mode library to wrap these ioctls, please reference xf86drm.h in libdrm for detailed explanation. The general steps to use the libdrm are: open/drmOpen /dev/dri/cardN device nodecall drmModeGetResources, get all the drmModeRes resources. Resources include all the fb, crtc, encoder, connector, etc.loop through drmModeRes structure, call drmModeGetConnector, get the first connected connector(DRM_MODE_CONNECTED)drmModeConnector stores all the supporting mode, choose one from them.loop through drmModeRes，call drmModeGetEncoder. If the encoder matches with the selected mode, save the drmModeModeInfo for later use.create kms_driver, create buffer object，get the pitch of the BO，and map the BO to user space.draw on the BO using cairo or whatever graphic toolbox you like.get original display mode by calling drmModeGetCrtc, this will be used after program exit to restore the original mode.get frame buffer ID by calling drmModeAddFB, whose argument is BO handle.call drmModeSetCrtc with frame buffer ID, the BO attached with the FB is outputed to display.2.libdrm编译 2.1.libdrm-1.0.0代码下载： https://dri.freedesktop.org/libdrm/编译： ./configure make -j8 编译报错： xf86drm.c:66:12: fatal error: X11/Xlibint.h: No such file or directory # include ^~~~~~~~~~~~~~解决：sudo apt install libx11-dev 安装： sudo make install uos@uos-PC:/usr/local/lib$ ls -l 总用量 420 -rw-r--r-- 1 root staff 254476 1月 29 17:24 libdrm.a -rwxr-xr-x 1 root staff 783 1月 29 17:24 libdrm.la lrwxrwxrwx 1 root staff 15 1月 29 17:24 libdrm.so -> libdrm.so.1.0.0 lrwxrwxrwx 1 root staff 15 1月 29 17:24 libdrm.so.1 -> libdrm.so.1.0.0 -rwxr-xr-x 1 root staff 154248 1月 29 17:24 libdrm.so.1.0.0 drwxr-sr-x 2 root staff 4096 1月 29 17:24 pkgconfig drwxrwsr-x 4 root staff 4096 1月 12 17:09 python2.7 drwxrwsr-x 3 root staff 4096 1月 12 17:09 python3.72.2.libdrm 源码编译： 17 Compiling 18 --------- 19 20 To set up meson: 21 22 meson builddir/ 23 24 By default this will install into /usr/local, you can change your prefix 25 with --prefix=/usr (or `meson configure builddir/ -Dprefix=/usr` after 26 the initial meson setup). 27 28 Then use ninja to build and install: 29 30 ninja -C builddir/ install 31 32 If you are installing into a system location you will need to run install 33 separately, and as root.编译安装命令： sudo apt install meson meson builddir/ --prefix=/home/work/libdrm_install sudo ninja -C builddir/ install 3.APIs DRM驱动会在/dev/dri下创建设备节点： root@uos-PC:/dev/dri# ls -l 总用量 0 drwxr-xr-x 2 root root 80 1月 29 17:01 by-path crw-rw----+ 1 root video 226, 0 1月 29 17:01 card0 crw-rw----+ 1 root render 226, 128 1月 29 17:01 renderD1283.1.drmOpen() drmOpen ->drmOpenByBusid ->fd = drmOpenMinor(i, 1); //dev/dri/card* Looks up the specified name and bus ID, and opens the device found. The entry in /dev/dri is created if necessary and if called by root. 550 int drmOpen(const char *name, const char *busid) 551 { 552 #ifdef XFree86Server 553 if (!drmAvailable() && name != NULL) { 554 /* try to load the kernel */ 555 if (!xf86LoadKernelModule(name)) { 556 ErrorF("[drm] failed to load kernel module \"%s\"\n", 557 name); 558 return -1; 559 } 560 } 561 #endif 562 563 if (busid) { 564 int fd; 565 566 fd = drmOpenByBusid(busid); 567 if (fd >= 0) 568 return fd; 569 } 570 if (name) 571 return drmOpenByName(name); 572 return -1; 573 }3.2.drmModeGetResources retrieve current display configuration information. drmModeGetResources allocates, populates, and returns a drmModeRes structure containing information about the current display configuration. The structure contains the following fields: typedef struct _drmModeRes { int count_fbs; uint32_t *fbs; int count_crtcs; uint32_t *crtcs; int count_connectors; uint32_t *connectors; int count_encoders; uint32_t *encoders; uint32_t min_width, max_width; uint32_t min_height, max_height; } drmModeRes, *drmModeResPtr; 下图显示各个组件，以及组件之间的关联关系。在DRM的函数名中称作资源（Resource）。如drmModeGetResources()。 显示设备的设置、状态，保存在若干结构、变量中，如下图。如drmModeModeInfo，保存设备大小，刷新率。drmModeConnection保存连接状态。 4.Uos kernel libdrm uos@uos-PC:/usr/lib/x86_64-linux-gnu$ ls -l libdrm* lrwxrwxrwx 1 root root 22 9月 24 14:52 libdrm_amdgpu.so.1 -> libdrm_amdgpu.so.1.0.0 -rw-r--r-- 1 root root 43400 9月 24 14:52 libdrm_amdgpu.so.1.0.0 lrwxrwxrwx 1 root root 21 9月 24 14:52 libdrm_intel.so.1 -> libdrm_intel.so.1.0.0 -rw-r--r-- 1 root root 147248 9月 24 14:52 libdrm_intel.so.1.0.0 lrwxrwxrwx 1 root root 23 9月 24 14:52 libdrm_nouveau.so.2 -> libdrm_nouveau.so.2.0.0 -rw-r--r-- 1 root root 39216 9月 24 14:52 libdrm_nouveau.so.2.0.0 lrwxrwxrwx 1 root root 22 9月 24 14:52 libdrm_radeon.so.1 -> libdrm_radeon.so.1.0.1 -rw-r--r-- 1 root root 51392 9月 24 14:52 libdrm_radeon.so.1.0.1 lrwxrwxrwx 1 root root 15 9月 24 14:52 libdrm.so.2 -> libdrm.so.2.4.0 -rw-r--r-- 1 root root 76448 9月 24 14:52 libdrm.so.2.4.05.modetest 应用 它是由 libdrm 提供的测试程序，可以查询显示设备的特性，进行基本的显示测试，以及设置显示的模式。 编译生成目录：libdrm/builddir/tests/modetest modetest 查看帮助信息 $ modetest -h usage: modetest [-acDdefMPpsCvrw] Query options: -c list connectors -e list encoders -f list framebuffers -p list CRTCs and planes (pipes) Test options: ... Generic options: -d drop master after mode set -M module use the given driver -D device use the given device Default is to dump all info.refer to https://waynewolf.github.io/2012/09/05/libdrm-samples/https://www.jianshu.com/p/4a6820b94e3eLinux DRM API - NVIDIAhttps://docs.mesa3d.org/meson.htmlhttps://zhuanlan.zhihu.com/p/341895843https://software.intel.com/content/www/us/en/develop/documentation/intel-joule-getting-started/top/programmers-guide/hdmi-display-and-graphics/graphics-framework.html |
每种资源的结构都定义了一个成员，唯一标识这个资源。如drmModeCrtc的crtc_id、drmModeConnector的connector_id、drmModeEncoder的encoder_id、drmModePlane的plane_id。
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