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Date:   Thu, 2 Sep 2021 17:12:32 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     "Sa, Nuno" <Nuno.Sa@analog.com>
Cc:     Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 14/16] iio: adc: max1027: Consolidate the end of
 conversion helper
Message-ID: <20210902171232.450a6d62@xps13>
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References: <20210818111139.330636-1-miquel.raynal@bootlin.com>
        <20210818111139.330636-15-miquel.raynal@bootlin.com>
        <20210830113716.1f7cdc6f@jic23-huawei>
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Hi Nuno,

"Sa, Nuno" <Nuno.Sa@analog.com> wrote on Mon, 30 Aug 2021 12:44:48
+0000:

> > -----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.

I implemented it your way, but I think I found a situation that was not
fully handled (the 3rd), which makes the handler very complicated
as we need to handle all the following cases:
1/ no trigger, irq enabled -> single read EOC interrupt
2/ external trigger, no irq -> handle the whole conversion process
3/ external trigger, irq enabled -> handle the whole conversion process
   but also have a dedicated condition to handle the EOC interrupt
   properly (fortunately this is a threaded handler that can be
   preempted): we need to wait from the handler itself that the
   handler gets called again: the first time it is executed as
   "pollfunc", the second time as "EOC interrupt". In the second
   instance, call complete() in order to deliver the first running
   instance of the handler and continue until the reading part.
4/ cnvst trigger, irq enabled -> only reads the data.
5/ cnvst trigger, irq disabled -> not possible.

I added a lot of comments to make it clearer.

> 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?

I renamed it to make it clear, but this is already a threaded handler.

Thanks,
Miquèl