Re: [PATCH v3 1/6] dt-bindings: iio: introduce trigger providers, consumers

[Fabrice Gasnier]

On 03/15/2017 08:25 PM, Rob Herring wrote:
> On Sun, Mar 05, 2017 at 12:13:36PM +0000, Jonathan Cameron wrote:
>> On 05/03/17 11:43, Jonathan Cameron wrote:
>>> On 03/03/17 06:21, Rob Herring wrote:
>>>> On Tue, Feb 28, 2017 at 05:51:14PM +0100, Fabrice Gasnier wrote:
>>>>> Document iio provider and consumer bindings.
>>>>>
>>>>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
>>>>> ---
>>>>>  .../devicetree/bindings/iio/iio-bindings.txt       | 38 ++++++++++++++++++++++
>>>>>  1 file changed, 38 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/iio/iio-bindings.txt b/Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>>> index 68d6f8c..01765e9 100644
>>>>> --- a/Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>>> +++ b/Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>>> @@ -95,3 +95,41 @@ vdd channel is connected to output 0 of the &ref device.
>>>>>  		io-channels = <&adc 10>, <&adc 11>;
>>>>>  		io-channel-names = "adc1", "adc2";
>>>>>  	};
>>>>> +
>>>>> +==IIO trigger providers==
>>>>> +Sources of IIO triggers can be represented by any node in the device
>>>>> +tree. Those nodes are designated as IIO trigger providers. IIO trigger
>>>>> +consumer uses a phandle and an IIO trigger specifier to connect to an
>>>>> +IIO trigger provider.
>>>>> +An IIO trigger specifier is an array of one or more cells identifying
>>>>> +the IIO trigger output on a device. The length of an IIO trigger
>>>>> +specifier is defined by the value of a #io-trigger-cells property in
>>>>> +the IIO trigger provider node.
>>>>> +
>>>>> +Required properties:
>>>>> +#io-trigger-cells:
>>>>> +		Number of cells in an IIO trigger specifier; Typically
>>>>> +		0 for nodes with a simple IIO trigger output.
>>>>> +
>>>>> +Example:
>>>>> +	trig0: interrupt-trigger0 {
>>>>> +		#io-trigger-cells = <0>;
>>>>> +		compatible = "interrupt-trigger";
>>>>> +		interrupts = <11 0>;
>>>>> +		interrupt-parent = <&gpioa>;
>>>>> +	}
>>>>> +
>>>>> +==IIO trigger consumers==
>>>>> +Required properties:
>>>>> +- io-triggers:	List of phandle representing the IIO trigger specifier.
>>>>> +
>>>>> +Optional properties:
>>>>> +- io-trigger-names :
>>>>> +		List of IIO trigger name strings that matches elements
>>>>> +		in 'io-triggers' list property.
>>>>> +
>>>>> +Example:
>>>>> +	some_trigger_consumer {
>>>>> +		io-triggers = <&trig0>;
>>>>> +		io-trigger-names = "mytrig";
>>>>> +	}
>>>>
>>>> I have some reservations about this. We could just as easily add the 
>>>> interrupt directly to the consumer node and use "trigger" for a standard 
>>>> interrupt name. So the question is whether this extra level of 
>>>> indirection is needed? 
>>>
>>> First thing to note here, is that Fabrice's use of the generic interrupt
>>> trigger is an extremely 'unusual' one! Normal use case is that we have
Hi Rob, Jonathan,

Yes, I agree this is unusual.

>>> a random gpio pin providing interrupts to driver triggering on random
>>> devices - there need be no association between the two whatsoever.
>>> So what we are doing here is 'allowing' an interrupt to provide a trigger.
>>> It's not necessarily the one going to be used by any particular device
>>> driver.  The decision of which trigger to use is definitely one for
>>> userspace, not something that should be configured in to the device tree.
>>>
>>> For this particular case you could in theory just do it by using an interrupt
>>> as you describe.  Ultimately though we should be able to play more complex
>>> games with this device and having it able to handle any trigger - which 
>>> includes those not using the direct hardware route.  It'll be up to the
>>> driver to figure out when it can use the fast method and when it can't.
Agreed. Still, to benefit from hw capabilities, driver needs to have a
way to identify a particular trigger as a direct hardware route, or not
(and then default software handling, btw, that still needs to be
addressed in stm32-adc). DT Provider/consumer may help to achieve this.

>>>
>>> Conversely, even when we are using this hardware route to drive the
>>> triggering it should be possible to hang off a device to be triggered
>>> by the interrupt via the kernel rather than directly. 
>>>
>>> So from a device tree point of view we are just describing the fact that
>>> there is a pin, which may be used to trigger something.  What that something
>>> is, is a question for userspace not the device tree.
>>>
>> Ah, I'm half asleep this morning.  Clearly there is a more general follow
>> up question.  If we are arguing these are generic, why are we setting
>> up the mapping in device tree?
>>
>> My gut feeling is we shouldn't be.  So I think we need the first chunk
>> above but the latter part should be a job for userspace not the devicetree.
> 
> So you mean keep the provider side, but get rid of the consumer? That 
> makes sense to me.
In case getting rid of the consumer part, I still need one way, on
consumer side (stm32-adc) to specifically map EXTI signal in ADC
hardware, do some checks on trigger to validate hardware route.
I'm not sure how to handle this if I get rid of consumer part.
Shall I use something else not mentioned here? (put trigger dt node as
child node of stm32 adc, then use dev bus? ...)

Another way is as suggested by Rob in earlier comment: directly use this
interrupt in consumer dt node, e.g. in stm32-adc node. And register
relevant trigger and so on, from stm32-adc driver.
Please advise.

Thanks for reviewing
Best Regards,
Fabrice
> 
> Rob
>