Re: [PATCHv8 07/15] cec: add HDMI CEC framework

On Tue, Aug 18, 2015 at 11:00:20AM +0100, Russell King - ARM Linux wrote:

On Tue, Aug 18, 2015 at 10:26:32AM +0200, Hans Verkuil wrote:

...

• /* Part 2: Initialize and register the character device */
• cdev_init(&cecdev->cdev, &cec_devnode_fops);
• cecdev->cdev.owner = owner;
• ret = cdev_add(&cecdev->cdev, MKDEV(MAJOR(cec_dev_t), cecdev->minor),

• 							1);
  

• if (ret < 0) {

• pr_err("%s: cdev_add failed\n", __func__);
  

• goto error;
  

• }
• /* Part 3: Register the cec device */
• cecdev->dev.bus = &cec_bus_type;
• cecdev->dev.devt = MKDEV(MAJOR(cec_dev_t), cecdev->minor);
• cecdev->dev.release = cec_devnode_release;
• if (cecdev->parent)

• cecdev->dev.parent = cecdev->parent;
  

• dev_set_name(&cecdev->dev, "cec%d", cecdev->minor);
• ret = device_register(&cecdev->dev);

It's worth pointing out that you can greatly simplify the lifetime handling (you don't need to get and put cecdev->dev) if you make the cdev a child of the cecdev->dev.

If you grep for kobj.parent in drivers/ you'll see many drivers are doing this.

cecdev->cdev.kobj.parent = &cecdev->dev.kobj;

but you will need to call device_initialize() on cecdev->dev first, and use device_add() here.

This is basically a requirement if one embeds both device and a cdev into the same structure. Trying to do get/put in the driver is racy, you need to let framework know (by setting cdve's parent to the device structure).

Thanks.