On Thu, Apr 29, 2021 at 09:56:09AM +0900, ckim@xxxxxxxxxx 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
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