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SubjectRe: [PATCH v2 2/3] iio: adc: hx711: optimize performance in read cycle
On Mon, 9 Sep 2019 14:37:48 +0200
Andreas Klinger <ak@it-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@it-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!

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;

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