On Thu, Apr 29, 2021 at 09:56:09AM +0900, ckim@etri.re.kr wrote:
Hi, Greg KH,
To me cdev_device_add seems to be calling only cdev_add(below). In this case since dev->devt already holds dev_t value ("hl%d"), it just sets cdev_set_parent and cdev_add.
int cdev_device_add(struct cdev *cdev, struct device *dev) { int rc = 0;
if (dev->devt) { cdev_set_parent(cdev, &dev->kobj);
rc = cdev_add(cdev, dev->devt, 1); if (rc) return rc; }
rc = device_add(dev);
Right here is the line you are looking for. device_create() is a wrapper around a call to device_initialize() and device_add(). To use cdev_device_add() you have to have already called device_initialize() which the habannalabs code already did. Only on device_add() is the device really "added" to the driver core, and the uevents are sent out and lots of other stuff happens. device_create() wraps a lot of housekeeping logic up into a simpler call if your driver doesn't need that level of flexibility, but there is no requirement to call only it at all. Hope this helps, greg k-h