linux-kernel - Re: [PATCH 1/2] iio: light: ltr390: Add sysfs attribute to report data freshness

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Message-ID: <7e70075d-f91f-4ea8-b5e5-ccec6fba425d@baylibre.com>
Date: Thu, 24 Jul 2025 12:41:48 -0500
From: David Lechner <dlechner@...libre.com>
To: Akshay Jindal <akshayaj.lkd@...il.com>,
 Jonathan Cameron <jic23@...nel.org>
Cc: anshulusr@...il.com, nuno.sa@...log.com, andy@...nel.org,
 shuah@...nel.org, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] iio: light: ltr390: Add sysfs attribute to report
 data freshness

On 7/24/25 11:55 AM, Akshay Jindal wrote:
> On Thu, Jul 24, 2025 at 6:09 PM Jonathan Cameron <jic23@...nel.org> wrote:
>> Agreed.  Is the interrupt wired on this board?  If it is and you
>> want to do filtering with the knowledge that the data is fresh then
>> add a data ready trigger and buffered capture support.
>> It's a much bigger job, but it is standard ABI and as such of more
>> general use.
>>
>> Jonathan
>>
> Yes, the interrupt is wired in and enabled.
> 
> For LTR390, data_freshness is not the same as data-ready.
> Here the sensor does not support a data-ready interrupt.
> It only supports threshold violation interrupts where thresholds are
> configurable.
> LTR390 datasheet Pg 17:
> https://optoelectronics.liteon.com/upload/download/DS86-2015-0004/LTR-390UV_Final_%20DS_V1%201.pdf
> 
> Correct me, if I am wrong, but as per my understanding, trigger based interrupts
> are more appropriate where the application requires storing multiple samples
> in a buffer at specific time intervals, provided the sensor supports
> data-ready interrupts.
> 

Interrupts works just as well for single samples when devices have a
data ready signal. But you are right, that doesn't help us here
since the interrupt is just for threshold alerts.