[PATCH 2/5] iio: at91: Use different prescal, startup mask in MR for different IP

Jonathan Cameron jic23 at kernel.org
Tue Jul 16 15:03:38 EDT 2013

On 07/16/2013 12:30 PM, Thomas Petazzoni wrote:
> Dear Nicolas Ferre,
> On Tue, 16 Jul 2013 10:46:28 +0200, Nicolas Ferre wrote:
>>> Ok, that make sense. I will use compatible names for the capabilities in
>>> next version. Thanks.
>> Hold on a little bit Josh, I know that Jean-Christophe is not in favor 
>> of the use of multiple compatible strings. So, as the code is already 
>> there, let's wait and see if we find another argument...
> I've asked exactly this question last week at Linaro Connect during the
> ARM SoC consolidation panel/discussion, where Grant Likely, Arnd
> Bergmann, Olof and others were answering Device Tree related questions.
> My question, which precisely had the at91-adc DT binding in mind was
> precisely whether we should use different compatible properties to
> identify different revisions of an IP block and let the driver handle
> those differences, or whether the DT binding should provide sufficient
> properties (register offsets, bit numbers, etc.) to make the driver
> independent of the IP revisions. And clearly, the answer was that
> different compatible properties should be used to identify the
> different versions of the IP block, and the driver should abstract out
> the differences. I.e, was has been done for at91-adc is completely the
> opposite of the best practices for Device Tree on ARM.
> See
> http://www.youtube.com/watch?v=zF_AXLgkFy4&feature=player_detailpage#t=1581s
> where I ask exactly this question, and get answers from Olof Johansson
> and Grant Likely. They clearly say that the solution of having separate
> compatible properties and a driver that handles the differences is the
> way to go. So the way at91-adc (and possibly other at91 drivers) is
> using the Device Tree is wrong, there should have been multiple
> compatible properties. It's a shame because this is something we did say
> when we submitted at91-adc and during the reviews, but the maintainer
> wasn't listening to our comments...

Thanks for getting some clarity on this Thomas.  So I'll ask the somewhat obvious
question - how do we unwind from where we are to where we want to be wrt to the

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