linux-kernel - Re: [PATCH v2 2/3] iio: adc: hx711: optimize performance in read cycle

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Date:   Tue, 22 Oct 2019 12:58:32 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andreas Klinger <ak@...klinger.de>
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] iio: adc: hx711: optimize performance in read
 cycle

On Sun, 15 Sep 2019 13:59:48 +0100
Jonathan Cameron <jic23@...nel.org> wrote:

> On Mon, 9 Sep 2019 14:37:48 +0200
> Andreas Klinger <ak@...klinger.de> wrote:
> 
> > Set gain in hx711_reset() to its default value after a reset cycle. This
> > omits one precautionary read cycle, because the read is performed in
> > hx711_set_gain_for_channel() anyway if gain has changed.
> > 
> > Check for DOUT low and if its high wait some time if it goes down
> > instead of doing a blind reset cycle when DOUT is not down.
> > 
> > This is a performance optimization which allows to query the sensor with
> > a higher frequency.
> > 
> > Signed-off-by: Andreas Klinger <ak@...klinger.de>  
> Hi Andreas,
> 
> This one seems to have a slightly non trivial interaction with patch 1
> so will have to wait until the fixes-togreg branch works it's way back
> around to the upstream for the togreg branch.   Give me a poke if I seem
> to have lost it!
Applied.

Thanks,

Jonathan

> 
> Thanks,
> 
> Jonathan
> 
> > ---
> >  drivers/iio/adc/hx711.c | 23 +++++------------------
> >  1 file changed, 5 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
> > index 0678964dbd21..c8686558429b 100644
> > --- a/drivers/iio/adc/hx711.c
> > +++ b/drivers/iio/adc/hx711.c
> > @@ -23,6 +23,7 @@
> >  
> >  /* gain to pulse and scale conversion */
> >  #define HX711_GAIN_MAX		3
> > +#define HX711_RESET_GAIN	128
> >  
> >  struct hx711_gain_to_scale {
> >  	int			gain;
> > @@ -100,7 +101,6 @@ struct hx711_data {
> >  
> >  static int hx711_cycle(struct hx711_data *hx711_data)
> >  {
> > -	int val;
> >  	unsigned long flags;
> >  
> >  	/*
> > @@ -186,8 +186,7 @@ static int hx711_wait_for_ready(struct hx711_data *hx711_data)
> >  
> >  static int hx711_reset(struct hx711_data *hx711_data)
> >  {
> > -	int ret;
> > -	int val = gpiod_get_value(hx711_data->gpiod_dout);
> > +	int val = hx711_wait_for_ready(hx711_data);
> >  
> >  	if (val) {
> >  		/*
> > @@ -203,22 +202,10 @@ static int hx711_reset(struct hx711_data *hx711_data)
> >  		msleep(10);
> >  		gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
> >  
> > -		ret = hx711_wait_for_ready(hx711_data);
> > -		if (ret)
> > -			return ret;
> > -		/*
> > -		 * after a reset the gain is 128 so we do a dummy read
> > -		 * to set the gain for the next read
> > -		 */
> > -		ret = hx711_read(hx711_data);
> > -		if (ret < 0)
> > -			return ret;
> > -
> > -		/*
> > -		 * after a dummy read we need to wait vor readiness
> > -		 * for not mixing gain pulses with the clock
> > -		 */
> >  		val = hx711_wait_for_ready(hx711_data);
> > +
> > +		/* after a reset the gain is 128 */
> > +		hx711_data->gain_set = HX711_RESET_GAIN;
> >  	}
> >  
> >  	return val;  
>