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

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Message-ID: <46a15539-6297-46d1-e923-712b82fa4a7f@kernel.org>
Date:   Sun, 5 Mar 2017 11:45:28 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Fabrice Gasnier <fabrice.gasnier@...com>,
        Rob Herring <robh@...nel.org>
Cc:     linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, mark.rutland@....com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        lars@...afoo.de, knaack.h@....de, pmeerw@...erw.net,
        benjamin.gaignard@...aro.org, benjamin.gaignard@...com,
        linus.walleij@...aro.org
Subject: Re: [PATCH v3 1/6] dt-bindings: iio: introduce trigger providers,
 consumers

On 03/03/17 09:32, Fabrice Gasnier wrote:
> On 03/03/2017 07:21 AM, 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@...com>
>>> ---
>>>  .../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
> Hi Rob,
> 
> Thanks for reviewing.
> 
> I hope I don't miss your point here... However, if I correctly
> understand it:
> Yes, this can be one way to get interrupt(s) directly from consumer node. Then, I understand consumer has to do exact same as what is being done in "iio_interrupt_trigger" for instance, basically:
> - request irq, alloc and register trigger, do irq handling to call
> trigger poll routine.
> 
> With current patchset, consumer is able to use standard trigger like
> "interrupt-trigger" from DT. Please note I propose to add OF support
> for it in current patchset (e.g. PATCHs 2 & 3). Currently only platform
> data is supported.
> 
> -> And, please refer to PATCHs 5 & 6, I need to have some way to identify interrupt line (connected in HW to STM32 ADC IP). Currently,
> this is best I came up with, trying to re-use, be generic, and to describe this HW in DT.
> 
> Of course, the other way is still valid. Also, I want to highlight,
> STM32 has other IP, e.g. DAC, where same can be re-used then. This
> will avoid having duplicates.
Just to jump back a stage.  The binding here isn't stm32 specific
at all.  In general this binding allows for triggering anything
(currently IIO) from an interrupt. Nothing more - so that is the
level at which it should be considered.
> 
>> interrupt name. So the question is whether this extra level of
>> indirection is needed?
> 
> Purpose is to be able to get one or more named trigger(s) on consumer
> side. Idea is to adopt similar 'philosophy' as in other bindings like
> pinctrl, clk... where consumer has possibility to get them by name.
> I hope this clarifies.
Again, taking this in the general sense rather than on the stm32:
flexibility - if it makes sense to expose something to userspace we
do.  We could in theory list all the possible interrupt sources that
might drive each device in a system and then expose that to userspace
but that is hideous!
> 
> Please advise,
> Best Regards,
> Fabrice
> 
>>
>> Rob
>>
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