Subject: Re: [PATCH] staging: iio: ad7606: use
 iio_device_{claim|release}_direct_mode()
To: Alison Schofield <amsfield22@gmail.com>, linux-iio@vger.kernel.org
References: <20160401165349.GA2678@d830.WORKGROUP>
Cc: lars@metafoo.de, knaack.h@gmx.de, Michael.Hennerich@analog.com,
        pmeerw@pmeerw.net, gregkh@linuxfoundation.org,
        devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org
From: Jonathan Cameron <jic23@kernel.org>
Message-ID: <5700DDB9.5060100@kernel.org>
Date: Sun, 3 Apr 2016 10:09:13 +0100
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On 01/04/16 17:53, Alison Schofield wrote:
> Two instances are moved to the new claim/release API:
> 
> In the first instance, the driver was using mlock followed by
> iio_buffer_enabled(). Replace that code with the new API to guarantee
> the device stays in direct mode. There is no change in driver behavior.
> 
> In the second instance, the driver was not using mlock to hold the
> device in direct mode, but should have been.  Here we introduce the
> new API to guarantee direct mode. This is a change in driver behavior.
> 
> Signed-off-by: Alison Schofield <amsfield22@gmail.com>
> ---
>  drivers/staging/iio/adc/ad7606_core.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/staging/iio/adc/ad7606_core.c b/drivers/staging/iio/adc/ad7606_core.c
> index 6dbc811..f914b8d 100644
> --- a/drivers/staging/iio/adc/ad7606_core.c
> +++ b/drivers/staging/iio/adc/ad7606_core.c
> @@ -88,12 +88,12 @@ static int ad7606_read_raw(struct iio_dev *indio_dev,
>  
>  	switch (m) {
>  	case IIO_CHAN_INFO_RAW:
> -		mutex_lock(&indio_dev->mlock);
> -		if (iio_buffer_enabled(indio_dev))
> -			ret = -EBUSY;
> -		else
> -			ret = ad7606_scan_direct(indio_dev, chan->address);
> -		mutex_unlock(&indio_dev->mlock);
> +		ret = iio_device_claim_direct_mode(indio_dev);
> +		if (ret)
> +			return ret;
> +
> +		ret = ad7606_scan_direct(indio_dev, chan->address);
> +		iio_device_release_direct_mode(indio_dev);
>  
>  		if (ret < 0)
>  			return ret;
> @@ -411,8 +411,9 @@ static irqreturn_t ad7606_interrupt(int irq, void *dev_id)
>  	struct iio_dev *indio_dev = dev_id;
>  	struct ad7606_state *st = iio_priv(indio_dev);
>  
> -	if (iio_buffer_enabled(indio_dev)) {
> +	if (!iio_device_claim_direct_mode(indio_dev))  {
>  		schedule_work(&st->poll_work);
> +		iio_device_release_direct_mode(indio_dev);
Unfortunately this won't work.  That interrupt is still in traditional non
threaded form.  This will take a mutex in a top half interrupt handler
where a sleep cannot occur.

I'm just wondering how expensive it would be to fix this by moving that over
to a threaded handler.  In the poll_work case (buffer) it would be cleaner to do
so. I'm really confused what the intended interrupt handler
is in here.  I 'think' the sequence is:

Trigger fires the convst pin whether in top half or the bottom half of
a threaded interrupt, but not both - I guess this works, if it is rather
'unusual'.

We then get a interrupt to indicate that it has finished conversion and that
filters through to actually fill the buffer via a traditional top half /
bottom half interrupt handler.

So if we were to convert that to a threaded interrupt (with no top half / non
threaded part), we could drop the schedule_work and just call
ad7606_poll_bh_to_ring from the thread handler.

In the direct read case I doubt we care about the delay in dropping to a
thread prior to signalling the data is ready.

Can't think why this driver is still in staging :)

Lars, any interest from Analog in getting this one cleaned up?  Also
do you have any test hardware, if we mess around with this interrupt handling?

Jonathan


>  	} else {
>  		st->done = true;
>  		wake_up_interruptible(&st->wq_data_avail);
>