Dealing with optional i2c devices in a devicetree

Hi,

I'm working on a new board and one feature it as is a plug-in module 
with an ADS7830 voltage monitor on it. This will be used during 
manufacturing to sanity check that various voltage rails are within 
expected ranges.

I have a dts entry for the device as below (with some omissions for the 
sake of clarity)

	soc {
		internal-regs {
			i2c@11000 {
				ads7830@48 {
					compatible = "ads7830";
					reg = <0x48>;
				};
			};
		};
	};

The problem is that when the manufacturing card is not installed the 
device still shows up in /sys/class/hwmon/hwmon0/ and 
/sys/bus/i2c/devices/0-0048/ despite it not actually being present. If I 
was using an old style initialization I could use 
i2c_new_probed_device() which I think would stop the drivers probe() 
function from being called

Looking at the ads7828_probe() function it doesn't actually do anything 
with the i2c device before calling hwmon_device_register(). Some hwmon 
drivers like lm73_probe() do attempt to read from the device and bail if 
the read fails. I can probably fix my problem by doing something similar 
in the ads7828_probe(), but there are other drivers that have a similar 
probe function.

Is there a better way of getting the devicetree machinery to avoid the 
call to the driver probe function in the first place?

Thanks,
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