linux-kernel - Re: [PATCH v4 2/3] iio: accel: Support Kionix/ROHM KX022A accelerometer

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Date:   Mon, 31 Oct 2022 06:25:25 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     Jonathan Cameron <jic23@...nel.org>
CC:     Matti Vaittinen <mazziesaccount@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dmitry Rokosov <DDRokosov@...rdevices.ru>,
        Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Cosmin Tanislav <demonsingur@...il.com>,
        Jagath Jog J <jagathjog1996@...il.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] iio: accel: Support Kionix/ROHM KX022A
 accelerometer

On 10/29/22 14:35, Jonathan Cameron wrote:
> On Mon, 24 Oct 2022 05:44:21 +0000
> "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com> wrote:
> 
>>>> +
>>>> +		if (fwnode_irq_get_byname(fwnode, "INT2") > 0)
>>>> +			dev_warn(dev, "Only one IRQ supported\n");
>>>
>>> Why?  If you get the both, only the first one will be used by the driver.
>>> Not really worth warning about the lack of features...
>>
>> My thinking regarding developing new device went along the lines:
>>
>> Precondition: The HW (and data-sheet) explain how there is two INT pins.
>> 1. Board designer reads the data-sheet and uses both INT pins.
>> 2. SW engineer finds the driver and reads the DT-binding description.
>> 3. SW engineer writes the DT-description and hopes everything "just
>> works". (Amount of hope is probably inversely proportional to the amount
>> of experience XD).
>> 4) SW engineer gives a first go to the sensor SW and notices everything
>> does not just magically work.
> 
> Ah but it does "work". We simply don't use one of the IRQs.  That's not
> normally a problem as there are lots of other features we don't fully
> support.  Not using something is not normally considered a problem.

I guess you're correct...

> So far I'm not seeing anything that doesn't work because we only support
> one IRQ.  There may be combinations of interrupts that are tricky to handle
> on one IRQ line (or may not be supported at the same time on a single line)
> but so far you don't support those anyway..  Adding a more informative warning
> when adding those features would be reasonable
> 
> "Feature X not supported as only a single IRQ line available".

... and I also fully agree with this. My thinking was stuck with each 
IRQ line having a purpose fixed by HW - which is not the case with this 
sensor.

Yours
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~