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

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Message-ID: <20250727141221.40e1824e@jic23-huawei>
Date: Sun, 27 Jul 2025 14:12:21 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Akshay Jindal <akshayaj.lkd@...il.com>, 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 Thu, 24 Jul 2025 12:41:48 -0500
David Lechner <dlechner@...libre.com> wrote:

> 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.
> 

Yeah.  I got thrown by the adfruit docs that say the interrupt can serve
this purpose. Clearly not from the datasheet.

Jonathan