[Ksummit-2013-discuss] ARM topic: Is DT on ARM the solution, or is there something better?

[Jonathan Cameron]

James Hogan <james.hogan at imgtec.com> wrote:
>On 21/10/13 23:51, Guenter Roeck wrote:
>> In my opinion, not being able to describe behavior (or what people
>refer
>> to as "describe how the hardware is used") is a severe limitation of
>> devicetree usage in Linux. That is not a devicetree limitation per
>se,
>> though, it is simply a matter of choice (or, in some cases, the
>ability
>> of those arguing for new bindings to sell those bindings as "hardware
>> description").
>
>I agree this is a real problem, and I think it hinders upstream
>submission, since platform data was permitted to describe behaviour as
>well as describe the hardware, and platform data is being replaced with
>DT which is only permitted to describe the hardware. How then should we
>specify the behaviour to the kernel?
>
>I've already mentioned specific examples of this on the "Clock DT
>bindings" thread, and would be very interested if anybody has thoughts
>about it:
>http://lkml.kernel.org/r/520E1DF5.4030409@imgtec.com

We have run into a kind of similar issue with IIO. We are interested in describing sensors
 adcs,DACs etc and providing both userspace access and in kernel access to other drivers.

 Lots of sensors are used for different
 purposes on different devices. Simple example is free fall detection vs vibration
 analysis vs input for an accelerometer. User space expects data from different
 subsystems. We handle that via 'bridge' drivers.  So need a way to specify which
 bridge driver cares about which channels.
It is not always 'wiring' but it usually is dictated by the product implementation. 
Some aspects of this have been discussed but they only cover the is an ADC wired to an
 accelerometer case rather than the using the same physical hardware for on or more
 unrelated purpose.
Perhaps this case could be pushed into user space but then we just have another board
 specific bit of code...

Just to add that for IIO device tree mostly works pretty well.
>
>Cheers
>James
>
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