linux-kernel - Re: [PATCH RFC v1 2/2] iio: light: rpr0521: Drop unnecessary checks for timestamp value

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Message-ID: <20240929103344.GA92011@vamoiridPC>
Date: Sun, 29 Sep 2024 12:33:44 +0200
From: Vasileios Amoiridis <vassilisamir@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Vasileios Amoiridis <vassilisamir@...il.com>, lars@...afoo.de,
	andy.shevchenko@...il.com, u.kleine-koenig@...gutronix.de,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v1 2/2] iio: light: rpr0521: Drop unnecessary checks
 for timestamp value

On Sat, Sep 28, 2024 at 04:15:27PM +0100, Jonathan Cameron wrote:
> On Sun, 22 Sep 2024 18:20:41 +0200
> Vasileios Amoiridis <vassilisamir@...il.com> wrote:
> 
> > The rpr0521_trigger_consumer_handler() is registered as the trigger
> > threaded handler in the devm_iio_triggered_buffer_setup() function.
> > This function is being called in 2 ways:
> > 
> > a) when there is a registered trigger being trigger like sysfs or hrt.
> > The call of the trigger handler (which is the iio_pollfunc_store_time())
> > follows which saves the timestamp and then, wakes up the trigger
> > threaded handler.
> > 
> > b) The irq handler is using the iio_trigger_poll_nested() which wakes
> > up the trigger threaded handler.
> > 
> > In both cases, the pf->timestamp has already been assigned a value
> > so there is no need to check if it is 0, neither to 0 it after
> > the push to the buffer.
> 
> Not quite right (I think).  The caller of iio_trigger_poll_nested() might not
> be this driver.  There are other potential triggers that are nested
> because of need to check some status register, but can still be used
> for other devices.   In theory you could drive light capture of
> the as3935 for when you want to know how bright it was just after
> a lightening strike :)
> 
> We don't have a general solution for timestamps when that
> happens, so this driver is papering over that with this code.
> 
> 
> Jonathan
> 

Hi Jonathan,

Thank you very much for the reply! I see your point, I also think I 
am wrong after all. I was just interested to see why this driver makes
it so different from the other ones when it is coming to trigger/irq
handling. Thank you very much for the explanation!

Cheers,
Vasilis

> 
> 
> > 
> > Signed-off-by: Vasileios Amoiridis <vassilisamir@...il.com>
> > ---
> >  drivers/iio/light/rpr0521.c | 8 +-------
> >  1 file changed, 1 insertion(+), 7 deletions(-)
> > 
> > diff --git a/drivers/iio/light/rpr0521.c b/drivers/iio/light/rpr0521.c
> > index 56f5fbbf79ac..ae6a22b91b8d 100644
> > --- a/drivers/iio/light/rpr0521.c
> > +++ b/drivers/iio/light/rpr0521.c
> > @@ -446,13 +446,8 @@ static irqreturn_t rpr0521_trigger_consumer_handler(int irq, void *p)
> >  	int err;
> >  
> >  	/* Use irq timestamp when reasonable. */
> > -	if (iio_trigger_using_own(indio_dev) && data->irq_timestamp) {
> > +	if (iio_trigger_using_own(indio_dev))
> >  		pf->timestamp = data->irq_timestamp;
> > -		data->irq_timestamp = 0;
> > -	}
> > -	/* Other chained trigger polls get timestamp only here. */
> > -	if (!pf->timestamp)
> > -		pf->timestamp = iio_get_time_ns(indio_dev);
> >  
> >  	err = regmap_bulk_read(data->regmap, RPR0521_REG_PXS_DATA,
> >  		data->scan.channels,
> > @@ -463,7 +458,6 @@ static irqreturn_t rpr0521_trigger_consumer_handler(int irq, void *p)
> >  	else
> >  		dev_err(&data->client->dev,
> >  			"Trigger consumer can't read from sensor.\n");
> > -	pf->timestamp = 0;
> >  
> >  	iio_trigger_notify_done(indio_dev->trig);
> >  
>