Robin Murphy <robin.murphy@arm.com> writes:

> On 16/05/18 14:37, Stefan Wahren wrote:
>> Recent VC4 firmware provides a hardware-independent way to retrieve the
>> under-voltage sensor on the following Raspberry Pi boards:
>>    - Raspberry Pi B+ (via GPIO on SoC)
>>    - Raspberry Pi A+ (via GPIO on SoC)
>>    - Raspberry Pi 2 B (via GPIO on SoC)
>>    - Raspberry Pi 3 B (via GPIO on port expander)
>>    - Raspberry Pi 3 B+ (via PMIC)
>> 
>> TODO:
>>    - try to make bcm2835 firmware a bus driver
>
> Do you actually need a DT binding? From the probe routine in patch 2 it 
> looks like this capability can be discovered dynamically by asking the 
> firmware, therefore it might be more straightforward for the firmware 
> driver itself to probe that and create a child device iff the feature is 
> present, which the hwmon driver can then bind to as a pure platform driver.

Agreed, let's skip doing this in DT.  I just switched the bcm2835-camera
driver over to not need DT, and I think you could do something similar
(and use the pdev->dev.parent to get at the firmware device).