246static int __driver_attach(struct device *dev, void *data)
247{
248 struct device_driver *drv = data;
249
250 /*
251 * Lock device and try to bind to it. We drop the error
252 * here and always return 0, because we need to keep trying
253 * to bind to devices and some drivers will return an error
254 * simply if it didn\'t support the device.
255 *
256 * driver_probe_device() will spit a warning if there
257 * is an error.
258 */
259
260 if (dev->parent) /* Needed for USB */
261 down(&dev->parent->sem);
262 down(&dev->sem);
//如果该设备尚没有匹配的driver，则尝试匹配。
263 if (!dev->driver)
264 driver_probe_device(drv, dev);
265 up(&dev->sem);
266 if (dev->parent)
267 up(&dev->parent->sem);
268
269 return 0;
270}
170/**
171 * driver_probe_device - attempt to bind device & driver together
172 * @drv: driver to bind a device to
173 * @dev: device to try to bind to the driver
174 *
175 * First, we call the bus\'s match function, if one present, which should
176 * compare the device IDs the driver supports with the device IDs of the
177 * device. Note we don\'t do this ourselves because we don\'t know the
178 * format of the ID structures, nor what is to be considered a match and
179 * what is not.
180 *
181 * This function returns 1 if a match is found, -ENODEV if the device is
182 * not registered, and 0 otherwise.
183 *
184 * This function must be called with @dev->sem held. When called for a
185 * USB interface, @dev->parent->sem must be held as well.
186 */
187int driver_probe_device(struct device_driver *drv, struct device *dev)
188{
189 int ret = 0;
190
191 if (!device_is_registered(dev))
192 return -ENODEV;
193 if (drv->bus->match && !drv->bus->match(dev, drv))
194 goto done;
195
196 pr_debug("bus: \'%s\': %s: matched device %s with driver %s/n",
197 drv->bus->name, __FUNCTION__, dev->bus_id, drv->name);
198
199 ret = really_probe(dev, drv);
200
201done:
202 return ret;
203}
193，如果该总线上的设备需要进行匹配，则验证是否匹配。对于platform总线，其匹配过程如下：
542/**
543 * platform_match - bind platform device to platform driver.
544 * @dev: device.
545 * @drv: driver.
546 *
547 * Platform device IDs are assumed to be encoded like this:
548 * "<name><instance>", where <name> is a short description of the type of
549 * device, like "pci" or "floppy", and <instance> is the enumerated
550 * instance of the device, like \'0\' or \'42\'. Driver IDs are simply
551 * "<name>". So, extract the <name> from the platform_device structure,
552 * and compare it against the name of the driver. Return whether they match
553 * or not.
554 */
555static int platform_match(struct device *dev, struct device_driver *drv)
556{
557 struct platform_device *pdev;
558
559 pdev = container_of(dev, struct platform_device, dev);
560 return (strncmp(pdev->name, drv->name, BUS_ID_SIZE) == 0);
561}
560，简单的进行字符串匹配，这也是我们强调platform_device和platform_driver中的name属性需要一致的原因。