Libdrm full analysis 21 - source code full analysis (18)

Continued from the previous article: Full analysis of libdrm 20 - Full analysis of source code (17)

This article refers to the following blog posts:

Thank you very much!

This article continues to explain the actual function macro definition in include/drm/drm.h. Starting from this article, we skip some of the middle macro definitions (29 in total) and go directly to the most commonly used and core macro definitions. For the analysis of these macro definitions skipped in the middle and some macro definitions skipped later, they will be completed one by one later. And starting from this article, we no longer just introduce the macro definition, but analyze it together with the wrapper function where it is located.

But before analyzing the specific macros and encapsulation functions, let's take a look at the simplest DRM application process.

The pseudo code is as follows:

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);
}

It can be seen that the general process of DRM is as follows:

(1) Open the graphics card device (/dev/dri/card0 in this example);
(2) Obtain the id of related resources, including: crtc, encoder, connector;
(3) Obtain the display mode of the connector;
(4) Create dumb buffer;
(5) Bind the created dumb buffer to the FB (FrameBuffer) object;
(6) Map the dumb buffer for user space drawing;
(7) Start displaying.

For ease of understanding, 2 code examples are given (refer to the routines in other blogs on the Internet).

Routine 1

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include <xf86drm.h>
#include <xf86drmMode.h>

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;
}

Routine 2

#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#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;
}

After the code is finished, the compilation and operation methods of the routine will be explained. Here, it is good to focus on the code itself.

Libdrm full analysis 21 - source code full analysis (18)

Guess you like