libdrm全解析二十一 —— 源码全解析（18）
接前一篇文章：libdrm全解析二十 —— 源码全解析（17）
本文参考以下博文：
DRM 驱动程序开发（VKMS）
特此致谢！
本文继续对include/drm/drm.h中实际功能宏定义进行讲解。从本篇文章开始，我们跳过中间的一些宏定义（共29个），直接进入到最为常用和核心的宏定义。对于这些中间跳过的宏定义以及后边略过的一些宏定义的分析，后续会逐一补全。并且从本篇文章开始，不再只仅仅介绍宏定义，而是连同其所在包装函数一起进行解析。
不过在解析具体的宏和封装函数之前，先来看一下最简单的DRM应用程序流程。
伪代码如下：
int main(int argc, char **argv)
{
/* open the drm device */
open("/dev/dri/card0");
/* get crtc/encoder/connector id */
drmModeGetResources(...);
/* get connector for display mode */
drmModeGetConnector(...);
/* create a dumb-buffer */
drmIoctl(DRM_IOCTL_MODE_CREATE_DUMB);
/* bind the dumb-buffer to an FB object */
drmModeAddFB(...);
/* map the dumb buffer for userspace drawing */
drmIoctl(DRM_IOCTL_MODE_MAP_DUMB);
mmap(...);
/* start display */
drmModeSetCrtc(crtc_id, fb_id, connector_id, mode);
}
可以看到，DRM一般流程如下：
（1）打开显卡设备（本例中为/dev/dri/card0）；
（2）获得相关资源的id，包括：crtc、encoder、connector；
（3）获得connector的显示模式；
（4）创建dumb buffer；
（5）绑定创建的dumb buffer到FB（FrameBuffer）对象；
（6）映射dumb buffer以进行用户空间绘制；
（7）开始显示。
为了便于理解，给出2个代码实例（参考网上其它博客中的例程）。
- 例程1
#define _GNU_SOURCE
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
struct buffer_object {
uint32_t width;
uint32_t height;
uint32_t pitch;
uint32_t handle;
uint32_t size;
uint8_t *vaddr;
uint32_t fb_id;
};
struct buffer_object buf;
static int modeset_create_fb(int fd, struct buffer_object *bo)
{
struct drm_mode_create_dumb create = {};
struct drm_mode_map_dumb map = {};
/* create a dumb-buffer, the pixel format is XRGB888 */
create.width = bo->width;
create.height = bo->height;
create.bpp = 32;
drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create);
/* bind the dumb-buffer to an FB object */
bo->pitch = create.pitch;
bo->size = create.size;
bo->handle = create.handle;
drmModeAddFB(fd, bo->width, bo->height, 24, 32, bo->pitch,
bo->handle, &bo->fb_id);
/* map the dumb-buffer to userspace */
map.handle = create.handle;
drmIoctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map);
bo->vaddr = mmap(0, create.size, PROT_READ | PROT_WRITE,
MAP_SHARED, fd, map.offset);
/* initialize the dumb-buffer with white-color */
memset(bo->vaddr, 0xff, bo->size);
return 0;
}
static void modeset_destroy_fb(int fd, struct buffer_object *bo)
{
struct drm_mode_destroy_dumb destroy = {};
drmModeRmFB(fd, bo->fb_id);
munmap(bo->vaddr, bo->size);
destroy.handle = bo->handle;
drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy);
}
int main(int argc, char **argv)
{
int fd;
drmModeConnector *conn;
drmModeRes *res;
uint32_t conn_id;
uint32_t crtc_id;
fd = open("/dev/dri/card0", O_RDWR | O_CLOEXEC);
res = drmModeGetResources(fd);
crtc_id = res->crtcs[0];
conn_id = res->connectors[0];
conn = drmModeGetConnector(fd, conn_id);
buf.width = conn->modes[0].hdisplay;
buf.height = conn->modes[0].vdisplay;
modeset_create_fb(fd, &buf);
drmModeSetCrtc(fd, crtc_id, buf.fb_id,
0, 0, &conn_id, 1, &conn->modes[0]);
getchar();
modeset_destroy_fb(fd, &buf);
drmModeFreeConnector(conn);
drmModeFreeResources(res);
close(fd);
return 0;
}
- 例程2
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "xf86drm.h"
#include "xf86drmMode.h"
#define uint32_t unsigned int
struct framebuffer{
uint32_t size;
uint32_t handle;
uint32_t fb_id;
uint32_t *vaddr;
};
static void create_fb(int fd,uint32_t width, uint32_t height, uint32_t color ,struct framebuffer *buf)
{
struct drm_mode_create_dumb create = {};
struct drm_mode_map_dumb map = {};
uint32_t i;
uint32_t fb_id;
create.width = width;
create.height = height;
create.bpp = 32;
drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create); //创建显存,返回一个handle
drmModeAddFB(fd, create.width, create.height, 24, 32, create.pitch,create.handle, &fb_id);
map.handle = create.handle;
drmIoctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map); //显存绑定fd，并根据handle返回offset
//通过offset找到对应的显存(framebuffer)并映射到用户空间
uint32_t *vaddr = mmap(0, create.size, PROT_READ | PROT_WRITE,MAP_SHARED, fd, map.offset);
for (i = 0; i < (create.size / 4); i++)
vaddr[i] = color;
buf->vaddr=vaddr;
buf->handle=create.handle;
buf->size=create.size;
buf->fb_id=fb_id;
return;
}
static void release_fb(int fd, struct framebuffer *buf)
{
struct drm_mode_destroy_dumb destroy = {};
destroy.handle = buf->handle;
drmModeRmFB(fd, buf->fb_id);
munmap(buf->vaddr, buf->size);
drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy);
}
int main(int argc, char **argv)
{
int fd;
struct framebuffer buf[3];
drmModeConnector *connector;
drmModeRes *resources;
uint32_t conn_id;
uint32_t crtc_id;
fd = open("/dev/dri/card0", O_RDWR | O_CLOEXEC); //打开card0，card0一般绑定HDMI和LVDS
resources = drmModeGetResources(fd); //获取drmModeRes资源,包含fb、crtc、encoder、connector等
conn_id = resources->connectors[0]; //获取connector id
crtc_id = resources->crtcs[0]; //获取crtc id
printf("conn_id is: %d\n", conn_id);
printf("crtc_id is: %d\n", crtc_id);
//conn_id = resources->connectors[1]; //获取connector id
//crtc_id = resources->crtcs[1]; //获取crtc id
//printf("conn_id is: %d\n", conn_id);
//printf("crtc_id is: %d\n", crtc_id);
connector = drmModeGetConnector(fd, conn_id); //根据connector_id获取connector资源
printf("hdisplay:%d vdisplay:%d\n",connector->modes[0].hdisplay,connector->modes[0].vdisplay);
create_fb(fd,connector->modes[0].hdisplay,connector->modes[0].vdisplay, 0xff0000, &buf[0]); //创建显存和上色
create_fb(fd,connector->modes[0].hdisplay,connector->modes[0].vdisplay, 0x00ff00, &buf[1]);
create_fb(fd,connector->modes[0].hdisplay,connector->modes[0].vdisplay, 0x0000ff, &buf[2]);
drmModeSetCrtc(fd, crtc_id, buf[0].fb_id,
0, 0, &conn_id, 1, &connector->modes[0]); //初始化和设置crtc，对应显存立即刷新
sleep(5);
drmModeSetCrtc(fd, crtc_id, buf[1].fb_id,
0, 0, &conn_id, 1, &connector->modes[0]);
sleep(5);
drmModeSetCrtc(fd, crtc_id, buf[2].fb_id,
0, 0, &conn_id, 1, &connector->modes[0]);
sleep(5);
release_fb(fd, &buf[0]);
release_fb(fd, &buf[1]);
release_fb(fd, &buf[2]);
drmModeFreeConnector(connector);
drmModeFreeResources(resources);
close(fd);
return 0;
}
后续讲完代码后，会讲解例程的编译和运行方法，这里重点关注代码本身就好。