linux-kernel - Re: [PATCH v6 2/2] iio: light: ROHM BH1745 colour sensor

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Date: Sat, 29 Jun 2024 18:50:46 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Mudit Sharma <muditsharma.info@...il.com>
Cc: lars@...afoo.de, krzk+dt@...nel.org, conor+dt@...nel.org,
 robh@...nel.org, linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, Ivan Orlov <ivan.orlov0322@...il.com>, Javier
 Carrasco <javier.carrasco.cruz@...il.com>
Subject: Re: [PATCH v6 2/2] iio: light: ROHM BH1745 colour sensor

On Sat, 29 Jun 2024 10:10:19 +0100
Mudit Sharma <muditsharma.info@...il.com> wrote:

> On 28/06/2024 20:37, Jonathan Cameron wrote:
> > Hi Mudit,
> > 
> > I'd failed on previous reviews to notice the odd trigger in here.
> > What is it, because it doesn't seem to be a dataready trigger as the device
> > doesn't seem to provide such an interrupt?  
> 
> Hi Jonathan,
> 
> Thank you for your review on this.
> 
> I've incorrect called it as a dataready trigger, I missed this as part 
> of my initial cleanup - apologies for the confusion caused by this. I 
> should potentially call it 'threshold' or 'dev'. Please suggest what you 
> think would be appropriate here.
> 
> The sensor has an active low interrupt pin which is connected to a GPIO 
> (input, pullup). When the sensor reading crosses value set in threshold 
> high or threshold low resisters, interrupt signal is generated and the 
> interrupt gets handled in 'bh1745_interrupt_handler()' (interrupt also 
> depends on number of consecutive judgements set in BH1745_PERSISTENCE 
> register)

This isn't really a trigger. Just report the event and don't register a trigger at
all. 

In theory we could have a trigger with these properties (and we did discuss
many years ago how to do this in a generic fashion) but today it isn't
something any standard userspace will understand how to use.

> 
> > 
> > Various other comments inline.  
> 
> Will address all for v7
> >  
> ...
> >> +static irqreturn_t bh1745_interrupt_handler(int interrupt, void *p)
> >> +{
> >> +	struct iio_dev *indio_dev = p;
> >> +	struct bh1745_data *data = iio_priv(indio_dev);
> >> +	int ret;
> >> +	int value;
> >> +
> >> +	ret = regmap_read(data->regmap, BH1745_INTR, &value);
> >> +	if (ret)
> >> +		return IRQ_NONE;
> >> +
> >> +	if (value & BH1745_INTR_STATUS) {
> >> +		guard(mutex)(&data->lock);
> >> +		iio_push_event(indio_dev,
> >> +			       IIO_UNMOD_EVENT_CODE(IIO_INTENSITY, data->int_src,
> >> +						    IIO_EV_TYPE_THRESH,
> >> +						    IIO_EV_DIR_EITHER),
> >> +			       iio_get_time_ns(indio_dev));  
> > 
> > What is happening here.  You always push out the event and use that as
> > a trigger?  This is an unusual trigger if it's appropriate to use it for
> > one at all.  You've called it a dataready trigger but it is not obvious
> > that this device provides any such signal.  
> 
> When an interrupt occurs, BH1745_INTR_STATUS bit is set in the 
> BH1745_INTR register. Event is only pushed out when the 
> BH1745_INTR_STATUS bit is set.
That bit is fine. My confusion is more about the trigger.  I think
the short answer is drop the next line and indeed all the code registering
a trigger as this device doesn't provide appropriate hardware.

> >> +
> >> +		iio_trigger_poll_nested(data->trig);
> >> +
> >> +		return IRQ_HANDLED;
> >> +	}
> >> +
> >> +	return IRQ_NONE;
> >> +}  
> 
> Best regards,
> Mudit Sharma
>