Re: [BKPATCH] bus notifiers for the generic device model

[Jeff Garzik <jgarzik@pobox.com>]

Patrick Mochel wrote:
> ===== drivers/base/bus.c 1.26 vs edited =====
> --- 1.26/drivers/base/bus.c	Sun Dec  1 23:22:04 2002
> +++ edited/drivers/base/bus.c	Wed Dec  4 12:02:41 2002
> @@ -228,6 +228,10 @@
>  {
>  	pr_debug("bound device '%s' to driver '%s'\n",
>  		 dev->bus_id,dev->driver->name);
> +
> +	if (dev->driver->start)
> +		dev->driver->start(dev);
> +
>  	list_add_tail(&dev->driver_list,&dev->driver->devices);
>  	sysfs_create_link(&dev->driver->kobj,&dev->kobj,dev->kobj.name);
>  }
> 
> I don't recall why the change was never done. Perhaps because of other 
> distractions, or it seemed like it would be too much of a PITA to convert 
> drivers to a two-step init sequence (though I think it could be done in a 
> compatible manner).


Possibly because of the "do it in open(2)" rule?

Ignoring the device model entirely, if a driver does a lot of 
talking-to-the-hardware in its probe phase, I consider it buggy, in 2.4 
or 2.5.

The network driver and chardev ones typically follow this rule quite 
well... probe is simple, just registering interfaces with the kernel. 
dev->open is where the driver should (and usually does) power-up the 
hardware, [re-]initialize it, etc.

So each time you come upon a driver that wants dev->driver->start(), 
look closely at the code and wonder why it can't perform the 
dev->driver->start() code in its interface's dev->open member.

	Jeff