xf86-video-intel源码分析7 —— intel_device.c和intel_driver.h（2）

接上一篇文章《xf86-video-intel源码分析6 —— intel_device.c和intel_driver.h（1）》，链接为：

xf86-video-intel源码分析6 —— intel_device.c和intel_driver.h（1）_蓝天居士的博客-CSDN博客

上一篇文章分析到了__intel_open_device函数，再列一下代码：

static int __intel_open_device(const struct pci_device *pci, const char *path)
{
	int fd;
 
	if (path == NULL) {
		if (pci == NULL)
			return -1;
 
		fd = __intel_open_device__pci(pci);
		if (fd == -1)
			fd = __intel_open_device__legacy(pci);
	} else
		fd = open_cloexec(path);
 
	return fd;
}

可以看到，函数共分为3条路径：

（1）当path和pci同时为空的时候，直接返回-1，甭往下走了；

（2）如果path为空而pci不为空，那么可以通过入参指针pci进行设备的打开。如果__intel_open_device_pci函数无法打开，还可以通过老版本__intel_open_device__legacy函数尝试打开；

（3）如果path本身就不空，也就是直接指定了路径，则直接通过open_cloexec函数打开。

我们由浅入深地进行分析，先来看第2个函数__intel_open_device_pci__legacy。

__intel_open_device__legacy函数在同文件中实现，代码如下：

static int __intel_open_device__legacy(const struct pci_device *pci)
{
	char id[20];
	int ret;
 
	snprintf(id, sizeof(id),
		 "pci:%04x:%02x:%02x.%d",
		 pci->domain, pci->bus, pci->dev, pci->func);
 
	ret = drmCheckModesettingSupported(id);
	if (ret) {
		if (load_i915_kernel_module() == 0)
			ret = drmCheckModesettingSupported(id);
		if (ret)
			return -1;
		/* Be nice to the user and load fbcon too */
		(void)xf86LoadKernelModule("fbcon");
	}
 
	return fd_set_nonblock(drmOpen(NULL, id));
}

一上来先通过snprintf函数生成id，id的内容为"pci:xxxx:xx:xx.x"。4个为x的部分分别代表域、总线、设备和功能。通过lspci命令可以看到相关内容，笔者电脑中的信息为：

$ lspci | cut -d : -f1-3
0000:00:00.0 Host bridge
0000:00:02.0 VGA compatible controller
0000:00:04.0 Signal processing controller
0000:00:06.0 System peripheral
0000:00:07.0 PCI bridge
0000:00:0d.0 USB controller
0000:00:0d.2 USB controller
0000:00:0e.0 RAID bus controller
0000:00:14.0 USB controller
0000:00:14.2 RAM memory
0000:00:14.3 Network controller
0000:00:15.0 Serial bus controller
0000:00:15.3 Serial bus controller
0000:00:16.0 Communication controller
0000:00:17.0 System peripheral
0000:00:1d.0 PCI bridge
0000:00:1d.1 PCI bridge
0000:00:1f.0 ISA bridge
0000:00:1f.3 Multimedia audio controller
0000:00:1f.4 SMBus
0000:00:1f.5 Serial bus controller
0000:2b:00.0 Ethernet controller
0000:2c:00.0 Unassigned class [ff00]
10000:e0:06.0 PCI bridge
10000:e0:17.0 SATA controller
10000:e1:00.0 Non-Volatile memory controller

因此，对于比着电脑来说，id的值应该为"pci:0000:00:02.0"（信息取自于VGA那一行）。

接下来调用drmCheckModesettingSupported函数对生成的id进行检查，看modesetting是否支持。drmCheckModesettingSupported函数当然不在xf86-video-intel源码中，也不在xorg-server源码中。那么它属于哪个包？

仍然用之前的方法，在/usr/include/下进行搜索，结果如下：

$ grep -rn "drmCheckModesettingSupported" /usr/include/
/usr/include/xf86drmMode.h:403:extern int drmCheckModesettingSupported(const char *busid);

而xf86drmMode.h来自于libdrm。链接暨上游地址为：

Mesa / drm · GitLab

drmCheckModesettingSupported函数源码如下：

/*
 * checks if a modesetting capable driver has attached to the pci id
 * returns 0 if modesetting supported.
 *  -EINVAL or invalid bus id
 *  -ENOSYS if no modesetting support
*/
drm_public int drmCheckModesettingSupported(const char *busid)
{
#if defined (__linux__)
	char pci_dev_dir[1024];
	int domain, bus, dev, func;
	DIR *sysdir;
	struct dirent *dent;
	int found = 0, ret;
 
	ret = sscanf(busid, "pci:%04x:%02x:%02x.%d", &domain, &bus, &dev, &func);
	if (ret != 4)
		return -EINVAL;
 
	sprintf(pci_dev_dir, "/sys/bus/pci/devices/%04x:%02x:%02x.%d/drm",
		domain, bus, dev, func);
 
	sysdir = opendir(pci_dev_dir);
	if (sysdir) {
		dent = readdir(sysdir);
		while (dent) {
			if (!strncmp(dent->d_name, "controlD", 8)) {
				found = 1;
				break;
			}
 
			dent = readdir(sysdir);
		}
		closedir(sysdir);
		if (found)
			return 0;
	}
 
	sprintf(pci_dev_dir, "/sys/bus/pci/devices/%04x:%02x:%02x.%d/",
		domain, bus, dev, func);
 
	sysdir = opendir(pci_dev_dir);
	if (!sysdir)
		return -EINVAL;
 
	dent = readdir(sysdir);
	while (dent) {
		if (!strncmp(dent->d_name, "drm:controlD", 12)) {
			found = 1;
			break;
		}
 
		dent = readdir(sysdir);
	}
 
	closedir(sysdir);
	if (found)
		return 0;
#elif defined (__FreeBSD__) || defined (__FreeBSD_kernel__)
	char sbusid[1024];
	char oid[128];
	int i, modesetting, ret;
	size_t len;
 
	/* How many GPUs do we expect in the machine ? */
	for (i = 0; i < 10; i++) {
		snprintf(oid, sizeof(oid), "hw.dri.%d.busid", i);
		len = sizeof(sbusid);
		ret = sysctlbyname(oid, sbusid, &len, NULL, 0);
		if (ret == -1) {
			if (errno == ENOENT)
				continue;
			return -EINVAL;
		}
		if (strcmp(sbusid, busid) != 0)
			continue;
		snprintf(oid, sizeof(oid), "hw.dri.%d.modesetting", i);
		len = sizeof(modesetting);
		ret = sysctlbyname(oid, &modesetting, &len, NULL, 0);
		if (ret == -1 || len != sizeof(modesetting))
			return -EINVAL;
		return (modesetting ? 0 : -ENOSYS);
	}
#elif defined(__DragonFly__)
	return 0;
#elif defined(__OpenBSD__)
	int	fd;
	struct drm_mode_card_res res;
	drmModeResPtr r = 0;
 
	if ((fd = drmOpen(NULL, busid)) < 0)
		return -EINVAL;
 
	memset(&res, 0, sizeof(struct drm_mode_card_res));
 
	if (drmIoctl(fd, DRM_IOCTL_MODE_GETRESOURCES, &res)) {
		drmClose(fd);
		return -errno;
	}
 
	drmClose(fd);
	return 0;
#endif
	return -ENOSYS;
}