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Date: Sun, 15 Jul 2018 09:38:43 +0100 From: Jonathan Cameron <jic23@...nel.org> To: Andreas Klinger <ak@...klinger.de> Cc: knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net, robh+dt@...nel.org, mark.rutland@....com, mchehab@...nel.org, davem@...emloft.net, gregkh@...uxfoundation.org, akpm@...ux-foundation.org, linus.walleij@...aro.org, rdunlap@...radead.org, devicetree@...r.kernel.org, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v5 2/3] iio: hx711: add delay until DOUT is ready On Tue, 10 Jul 2018 20:19:03 +0200 Andreas Klinger <ak@...klinger.de> wrote: > On a system with parasitic capacitance 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 <ak@...klinger.de> Applied, thanks. Jonathan > --- > drivers/iio/adc/hx711.c | 39 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 39 insertions(+) > > diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c > index 9430b54121e0..36b59d8957fb 100644 > --- a/drivers/iio/adc/hx711.c > +++ b/drivers/iio/adc/hx711.c > @@ -97,6 +97,14 @@ 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; > + u32 clock_frequency; > }; > > static int hx711_cycle(struct hx711_data *hx711_data) > @@ -110,6 +118,14 @@ 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, > @@ -120,6 +136,12 @@ static int hx711_cycle(struct hx711_data *hx711_data) > gpiod_set_value(hx711_data->gpiod_pd_sck, 0); > preempt_enable(); > > + /* > + * make it a square wave for addressing cases with capacitance on > + * PC_SCK > + */ > + ndelay(hx711_data->data_ready_delay_ns); > + > return val; > } > > @@ -458,6 +480,7 @@ 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 +553,22 @@ static int hx711_probe(struct platform_device *pdev) > hx711_data->gain_set = 128; > hx711_data->gain_chan_a = 128; > > + hx711_data->clock_frequency = 400000; > + ret = of_property_read_u32(np, "clock-frequency", > + &hx711_data->clock_frequency); > + > + /* > + * datasheet says the high level of PD_SCK has a maximum duration > + * of 50 microseconds > + */ > + if (hx711_data->clock_frequency < 20000) { > + dev_warn(dev, "clock-frequency too low - assuming 400 kHz\n"); > + hx711_data->clock_frequency = 400000; > + } > + > + hx711_data->data_ready_delay_ns = > + 1000000000 / hx711_data->clock_frequency; > + > platform_set_drvdata(pdev, indio_dev); > > indio_dev->name = "hx711";
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