linux-kernel - Re: [PATCH v2 4/4] iio: accel: adxl345: Add support for triggered buffer

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Message-ID: <19696c7f-a7c5-05d9-c58c-9a1d3588e75a@kernel.org>
Date:   Tue, 2 May 2017 17:08:52 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     linux-iio@...r.kernel.org, knaack.h@....de, lars@...afoo.de,
        pmeerw@...erw.net, dmitry.torokhov@...il.com,
        michael.hennerich@...log.com, daniel.baluta@...il.com,
        amsfield22@...il.com, florian.vaussard@...g-vd.ch,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] iio: accel: adxl345: Add support for triggered
 buffer

On 02/05/17 13:23, Eva Rachel Retuya wrote:
> On Mon, May 01, 2017 at 01:42:29AM +0100, Jonathan Cameron wrote:
> [...]
>> Few minor bits inline...  I'm a little bit in two minds about the 
>> holding up waiting for new data when using another trigger...
>>
>> Jonathan
> [...]
>>>  static int adxl345_read_raw(struct iio_dev *indio_dev,
>>> @@ -127,6 +151,10 @@ static int adxl345_read_raw(struct iio_dev *indio_dev,
>>>  
>>>  	switch (mask) {
>>>  	case IIO_CHAN_INFO_RAW:
>>> +		ret = iio_device_claim_direct_mode(indio_dev);
>>> +		if (ret)
>>> +			return ret;
>>> +
>>>  		mutex_lock(&data->lock);
>>>  		ret = adxl345_set_mode(data, ADXL345_POWER_CTL_MEASURE);
>>>  		if (ret < 0) {
>>> @@ -148,12 +176,14 @@ static int adxl345_read_raw(struct iio_dev *indio_dev,
>>>  		ret = regmap_bulk_read(data->regmap, chan->address, &regval,
>>>  				       sizeof(regval));
>>>  		mutex_unlock(&data->lock);
>>> +		iio_device_release_direct_mode(indio_dev);
>>>  		if (ret < 0) {
>>>  			adxl345_set_mode(data, ADXL345_POWER_CTL_STANDBY);
>>>  			return ret;
>>>  		}
>>>  
>>> -		*val = sign_extend32(le16_to_cpu(regval), 12);
>>> +		*val = sign_extend32(le16_to_cpu(regval),
>>> +				     chan->scan_type.realbits - 1)
>> This change isn't really needed, but I suppose it does little harm...
>>
>>>  		adxl345_set_mode(data, ADXL345_POWER_CTL_STANDBY);
>>>  
>>>  		return IIO_VAL_INT;
>>> @@ -186,6 +216,64 @@ static irqreturn_t adxl345_irq(int irq, void *p)
>>>  	return IRQ_NONE;
>>>  }
>>>  
>>> +static irqreturn_t adxl345_trigger_handler(int irq, void *p)
>>> +{
>>> +	struct iio_poll_func *pf = p;
>>> +	struct iio_dev *indio_dev = pf->indio_dev;
>>> +	struct adxl345_data *data = iio_priv(indio_dev);
>>> +	int ret;
>>> +
>>> +	mutex_lock(&data->lock);
>>> +	/* Make sure data is ready when using external trigger */
>> I 'think' this is only really relevant for the very first one.
>> After that general rule of thumb is that if an external trigger
>> is too quick - bad luck you'll get repeated data.
>>
>> One of the reasons we would want to use another trigger is to
>> support capture in parallel from several sensors - if we 'hold'
>> like this we'll get out of sync.
>>
>> As such I wonder if a better strategy would be to 'hold' for the
>> first reading in the buffer enable - thus guaranteeing valid
>> data before we start.  After that we wouldn't need to check this
>> here.
>>
> 
> Thanks for the explanation. If we are to go with this one, where to put
> it, preenable or postenable? I'm assuming the latter but would like to
> confirm.

postenable.  It could in theory be effected by a future use of the
update_scan_mode callback so should be after that.

J
> 
>> What do others think?
>>
> 
> Any other inputs are greatly appreciated.
> 
> Eva
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