RE: [PATCH 14/16] iio: adc: max1027: Consolidate the end of conversion helper

["Sa, Nuno" <Nuno.Sa@analog.com>]

> -----Original Message-----
> From: Jonathan Cameron <jic23@kernel.org>
> Sent: Monday, August 30, 2021 12:37 PM
> To: Miquel Raynal <miquel.raynal@bootlin.com>
> Cc: Lars-Peter Clausen <lars@metafoo.de>; Thomas Petazzoni
> <thomas.petazzoni@bootlin.com>; linux-iio@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH 14/16] iio: adc: max1027: Consolidate the end of
> conversion helper
> 
> On Wed, 18 Aug 2021 13:11:37 +0200
> Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> 
> > Now that we have a dedicated handler for End Of Conversion
> interrupts,
> > let's create a second path:
> > - Situation 1: we are using the external hardware trigger, a
> conversion
> >   has been triggered and the ADC pushed the data to its FIFO, we
> need to
> >   retrieve the data and push it to the IIO buffers.
> > - Situation 2: we are not using the external hardware trigger, hence
> we
> >   are likely waiting in a blocked thread waiting for this interrupt to
> >   happen: in this case we just wake up the waiting thread.
> >
> > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > ---
> >  drivers/iio/adc/max1027.c | 20 +++++++++++++++++---
> >  1 file changed, 17 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/iio/adc/max1027.c b/drivers/iio/adc/max1027.c
> > index 8d86e77fb5db..8c5995ae59f2 100644
> > --- a/drivers/iio/adc/max1027.c
> > +++ b/drivers/iio/adc/max1027.c
> > @@ -235,6 +235,7 @@ struct max1027_state {
> >  	struct iio_trigger		*trig;
> >  	__be16				*buffer;
> >  	struct mutex			lock;
> > +	bool				data_rdy;
> >  	bool				cnvst_trigger;
> >  	u8				reg ____cacheline_aligned;
> >  };
> > @@ -243,12 +244,22 @@ static
> DECLARE_WAIT_QUEUE_HEAD(max1027_queue);
> >
> >  static int max1027_wait_eoc(struct iio_dev *indio_dev)
> >  {
> > +	struct max1027_state *st = iio_priv(indio_dev);
> >  	unsigned int conversion_time =
> MAX1027_CONVERSION_UDELAY;
> > +	int ret;
> >
> > -	if (indio_dev->active_scan_mask)
> > -		conversion_time *= hweight32(*indio_dev-
> >active_scan_mask);
> > +	if (st->spi->irq) {
> > +		ret =
> wait_event_interruptible_timeout(max1027_queue,
> > +						       st->data_rdy, HZ /
> 1000);
> > +		st->data_rdy = false;
> > +		if (ret == -ERESTARTSYS)
> > +			return ret;
> > +	} else {
> > +		if (indio_dev->active_scan_mask)
> > +			conversion_time *= hweight32(*indio_dev-
> >active_scan_mask);
> >
> > -	usleep_range(conversion_time, conversion_time * 2);
> > +		usleep_range(conversion_time, conversion_time * 2);
> > +	}
> >
> >  	return 0;
> >  }
> > @@ -481,6 +492,9 @@ static irqreturn_t
> max1027_eoc_irq_handler(int irq, void *private)
> >  	if (st->cnvst_trigger) {
> >  		ret = max1027_read_scan(indio_dev);
> >  		iio_trigger_notify_done(indio_dev->trig);
> > +	} else {
> > +		st->data_rdy = true;
> > +		wake_up(&max1027_queue);
> 
> I can't see why a queue is appropriate for this.  Use a completion and
> have
> one per instance of the device.  No need for the flag etc in that case as
> complete() means we have had an interrupt.
> 

In the case that 'st-> cnvst_trigger' is not set but the spi IRQ
is present, we will wait until we get 'wake_up()' called from here. I wonder if
that is a good idea as the device own trigger is not being used. FWIW, I think this
sync logic is a bit confusing... I would still use the normal trigger infrastructure
('iio_trigger_generic_data_rdy_poll()') and use the 'cnvst_trigger' flag in the
trigger handler to manually start conversions + wait till eoc. But I might be missing
something though.

Regarding this handler, I just realized that this is the hard IRQ handler which
might end up calling 'max1027_read_scan()' which in turn calls 'spi_read()'. Am I
missing something here?

- Nuno Sá