Re: [PATCHv2 2/2] iio: dht11: Use new function ktime_get_resolution_ns()

[Harald Geyer <harald@ccbib.org>]

Hi Jonathan!

Jonathan Cameron writes:
> On 07/04/15 12:12, Harald Geyer wrote:
> > This cleans up the most ugly workaround in this driver. There are no
> > functional changes yet in the decoding algorithm, but we improve the
> > following things:
> >  * Get rid of spurious warning messages on systems with fast HRTIMER.
> >  * If the clock is not fast enough for decoding to work, we give
> >    up immediately.
> >  * In that case we return EAGAIN instead of EIO, so it's easier to
> >    discriminate causes of failure.
> > 
> > Returning EAGAIN is somewhat controversial: It's technically correct
> > as a faster clock might become available. OTOH once all clocks are
> > enabled this is a permanent error. There is no ECLOCKTOOSLOW error
> > code.
> > 
> > Signed-off-by: Harald Geyer <harald@ccbib.org>
> Looks good to me.  Will wait for comments on the first patch though
> before taking this... clearly that one will need a few acks if I take
> it through IIO!

The first patch has been merged via tip tree for 4.2 (is already available
in staging-next tree). Are you going to pick up this patch or do I need
to resend?

Thanks,
Harald

> Jonathan
> > ---
> > changes since V1:
> > call ktime_get_xxx() functions directly instead of using the wrappers
> > of the iio subsystem.
> > 
> >  drivers/iio/humidity/dht11.c |   42 ++++++++++++++++++++++--------------------
> >  1 files changed, 22 insertions(+), 20 deletions(-)
> > 
> > diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c
> > index 7d79a1a..4cb25dc 100644
> > --- a/drivers/iio/humidity/dht11.c
> > +++ b/drivers/iio/humidity/dht11.c
> > @@ -33,6 +33,7 @@
> >  #include <linux/delay.h>
> >  #include <linux/gpio.h>
> >  #include <linux/of_gpio.h>
> > +#include <linux/timekeeping.h>
> >  
> >  #include <linux/iio/iio.h>
> >  
> > @@ -87,23 +88,11 @@ static unsigned char dht11_decode_byte(int *timing, int threshold)
> >  	return ret;
> >  }
> >  
> > -static int dht11_decode(struct dht11 *dht11, int offset)
> > +static int dht11_decode(struct dht11 *dht11, int offset, int timeres)
> >  {
> > -	int i, t, timing[DHT11_BITS_PER_READ], threshold,
> > -		timeres = DHT11_SENSOR_RESPONSE;
> > +	int i, t, timing[DHT11_BITS_PER_READ], threshold;
> >  	unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
> >  
> > -	/* Calculate timestamp resolution */
> > -	for (i = 1; i < dht11->num_edges; ++i) {
> > -		t = dht11->edges[i].ts - dht11->edges[i-1].ts;
> > -		if (t > 0 && t < timeres)
> > -			timeres = t;
> > -	}
> > -	if (2*timeres > DHT11_DATA_BIT_HIGH) {
> > -		pr_err("dht11: timeresolution %d too bad for decoding\n",
> > -			timeres);
> > -		return -EIO;
> > -	}
> >  	threshold = DHT11_DATA_BIT_HIGH / timeres;
> >  	if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold)
> >  		pr_err("dht11: WARNING: decoding ambiguous\n");
> > @@ -126,7 +115,7 @@ static int dht11_decode(struct dht11 *dht11, int offset)
> >  	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
> >  		return -EIO;
> >  
> > -	dht11->timestamp = iio_get_time_ns();
> > +	dht11->timestamp = ktime_get_real_ns();
> >  	if (hum_int < 20) {  /* DHT22 */
> >  		dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
> >  					((temp_int & 0x80) ? -100 : 100);
> > @@ -154,7 +143,7 @@ static irqreturn_t dht11_handle_irq(int irq, void *data)
> >  
> >  	/* TODO: Consider making the handler safe for IRQ sharing */
> >  	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
> > -		dht11->edges[dht11->num_edges].ts = iio_get_time_ns();
> > +		dht11->edges[dht11->num_edges].ts = ktime_get_real_ns();
> >  		dht11->edges[dht11->num_edges++].value =
> >  						gpio_get_value(dht11->gpio);
> >  
> > @@ -170,10 +159,22 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
> >  			int *val, int *val2, long m)
> >  {
> >  	struct dht11 *dht11 = iio_priv(iio_dev);
> > -	int ret;
> > +	int ret, timeres;
> >  
> >  	mutex_lock(&dht11->lock);
> > -	if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {
> > +	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_ns()) {
> > +		timeres = ktime_get_resolution_ns();
> > +		if (DHT11_DATA_BIT_HIGH < 2*timeres) {
> > +			dev_err(dht11->dev, "timeresolution %dns too low\n",
> > +						timeres);
> > +			/* In theory a better clock could become available
> > +			 * at some point ... and there is no error code
> > +			 * that really fits better.
> > +			 */
> > +			ret = -EAGAIN;
> > +			goto err;
> > +		}
> > +
> >  		reinit_completion(&dht11->completion);
> >  
> >  		dht11->num_edges = 0;
> > @@ -208,7 +209,8 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
> >  		ret = dht11_decode(dht11,
> >  				dht11->num_edges == DHT11_EDGES_PER_READ ?
> >  					DHT11_EDGES_PREAMBLE :
> > -					DHT11_EDGES_PREAMBLE - 2);
> > +					DHT11_EDGES_PREAMBLE - 2,
> > +				timeres);
> >  		if (ret)
> >  			goto err;
> >  	}
> > @@ -274,7 +276,7 @@ static int dht11_probe(struct platform_device *pdev)
> >  		return -EINVAL;
> >  	}
> >  
> > -	dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1;
> > +	dht11->timestamp = ktime_get_real_ns() - DHT11_DATA_VALID_TIME - 1;
> >  	dht11->num_edges = -1;
> >  
> >  	platform_set_drvdata(pdev, iio);
> > 
>