On Sat, 23 Jun 2018 20:54:47 +0200 Andreas Klinger <[email protected]> wrote:
> On a system with parasitic capacities it turned out that DOUT is not ready > after 100 ns after PD_SCK has raised. A measurement showed almost 1000 ns > until DOUT has reached its correct value. > > With this patch its now possible to wait until data is ready. > > The wait time should not be higher than the maximum PD_SCK high time which > is corresponding to the datasheet 50000 ns. > > Signed-off-by: Andreas Klinger <[email protected]> This looks fine to me. Will pick up once we have a DT review for the binding. Thanks, Jonathan > --- > drivers/iio/adc/hx711.c | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c > index 9430b54121e0..41e26ef324ee 100644 > --- a/drivers/iio/adc/hx711.c > +++ b/drivers/iio/adc/hx711.c > @@ -97,6 +97,13 @@ struct hx711_data { > * 2x32-bit channel + 64-bit timestamp > */ > u32 buffer[4]; > + /* > + * delay after a rising edge on SCK until the data is ready DOUT > + * this is dependent on the hx711 where the datasheet tells a > + * maximum value of 100 ns > + * but also on potential parasitic capacities on the wiring > + */ > + u32 data_ready_delay_ns; > }; > > static int hx711_cycle(struct hx711_data *hx711_data) > @@ -110,6 +117,14 @@ static int hx711_cycle(struct hx711_data *hx711_data) > */ > preempt_disable(); > gpiod_set_value(hx711_data->gpiod_pd_sck, 1); > + > + /* > + * wait until DOUT is ready > + * it turned out that parasitic capacities are extending the time > + * until DOUT has reached it's value > + */ > + ndelay(hx711_data->data_ready_delay_ns); > + > val = gpiod_get_value(hx711_data->gpiod_dout); > /* > * here we are not waiting for 0.2 us as suggested by the datasheet, > @@ -458,6 +473,7 @@ static const struct iio_chan_spec hx711_chan_spec[] = { > static int hx711_probe(struct platform_device *pdev) > { > struct device *dev = &pdev->dev; > + struct device_node *np = dev->of_node; > struct hx711_data *hx711_data; > struct iio_dev *indio_dev; > int ret; > @@ -530,6 +546,13 @@ static int hx711_probe(struct platform_device *pdev) > hx711_data->gain_set = 128; > hx711_data->gain_chan_a = 128; > > + ret = of_property_read_u32(np, "data-ready-delay-ns", > + &hx711_data->data_ready_delay_ns); > + if (ret < 0) { > + dev_warn(dev, "data-ready-delay-ns not set - assuming 0 ns\n"); > + hx711_data->data_ready_delay_ns = 0; > + } > + > platform_set_drvdata(pdev, indio_dev); > > indio_dev->name = "hx711";
