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Message-ID: <20220901113503.GC2479@pengutronix.de>
Date: Thu, 1 Sep 2022 13:35:03 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Marco Felsch <m.felsch@...gutronix.de>
Cc: devicetree@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
kernel@...gutronix.de, linux-iio@...r.kernel.org,
linux-kernel@...r.kernel.org,
Andy Shevchenko <andy.shevchenko@...il.com>,
Rob Herring <robh+dt@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Jonathan Cameron <jic23@...nel.org>
Subject: Re: [PATCH v3 2/3] iio: adc: tsc2046: add vref support
Hi Marco,
On Thu, Sep 01, 2022 at 10:24:25AM +0200, Marco Felsch wrote:
> Hi Oleksij,
>
> sorry for jumping in, please see below.
>
> On 22-09-01, Oleksij Rempel wrote:
> > If VREF pin is attached, we should use external VREF source instead of
> > the internal. Otherwise we will get wrong measurements on some of channel
> > types.
> >
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > ---
> > drivers/iio/adc/ti-tsc2046.c | 64 +++++++++++++++++++++++++++++++-----
> > 1 file changed, 55 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ti-tsc2046.c b/drivers/iio/adc/ti-tsc2046.c
> > index 0d9436a69cbfb..bbc8b4137b0b1 100644
> > --- a/drivers/iio/adc/ti-tsc2046.c
> > +++ b/drivers/iio/adc/ti-tsc2046.c
> > @@ -8,6 +8,7 @@
> > #include <linux/bitfield.h>
> > #include <linux/delay.h>
> > #include <linux/module.h>
> > +#include <linux/regulator/consumer.h>
> > #include <linux/spi/spi.h>
> >
> > #include <asm/unaligned.h>
> > @@ -175,6 +176,9 @@ struct tsc2046_adc_priv {
> > u32 time_per_bit_ns;
> >
> > struct tsc2046_adc_ch_cfg ch_cfg[TI_TSC2046_MAX_CHAN];
> > + bool use_internal_vref;
> > + unsigned int vref_mv;
>
> We wouldn't need those members if we just enable/disable the regulator
> on demand. This would also be more power efficient.
Not really.
- it is reference voltage. There is no load.
- usually no one care to add extra switch to disable reference voltage
on a controller which should be enabled all the time any way.
- we add more CPU cycles on every access to enable/disable things, which are
usually never have dedicated regulator.
> > + struct regulator *vref_reg;
> > };
> >
> > #define TI_TSC2046_V_CHAN(index, bits, name) \
> > @@ -252,7 +256,9 @@ static u8 tsc2046_adc_get_cmd(struct tsc2046_adc_priv *priv, int ch_idx,
> > case TI_TSC2046_ADDR_AUX:
> > case TI_TSC2046_ADDR_VBAT:
> > case TI_TSC2046_ADDR_TEMP0:
> > - pd |= TI_TSC2046_SER | TI_TSC2046_PD1_VREF_ON;
> > + pd |= TI_TSC2046_SER;
> > + if (priv->use_internal_vref)
> > + pd |= TI_TSC2046_PD1_VREF_ON;
>
> Then this line would become:
ack. I agree here.
> + if (!priv->vref_reg)
> + pd |= TI_TSC2046_PD1_VREF_ON;
>
>
> > }
> >
> > return TI_TSC2046_START | FIELD_PREP(TI_TSC2046_ADDR, ch_idx) | pd;
> > @@ -468,7 +474,7 @@ static int tsc2046_adc_read_raw(struct iio_dev *indio_dev,
>
> This function needs to enable the vref_reg before the switch-case and
> disable it afterwards.
it will not enable power supply of this controller. There is no need to
do this.
> > * So, it is better to use external voltage-divider driver
> > * instead, which is calculating complete chain.
> > */
> > - *val = TI_TSC2046_INT_VREF;
> > + *val = priv->vref_mv;
> > *val2 = chan->scan_type.realbits;
> > return IIO_VAL_FRACTIONAL_LOG2;
> > }
> > @@ -781,22 +787,42 @@ static int tsc2046_adc_probe(struct spi_device *spi)
> > indio_dev->num_channels = dcfg->num_channels;
> > indio_dev->info = &tsc2046_adc_info;
> >
> > + priv->vref_reg = devm_regulator_get_optional(&spi->dev, "vref");
>
> This line would be enough and we could drop
>
> > + if (!IS_ERR(priv->vref_reg)) {
> > + ret = regulator_enable(priv->vref_reg);
> > + if (ret)
> > + return ret;
> > +
> > + ret = regulator_get_voltage(priv->vref_reg);
> > + if (ret < 0)
> > + goto err_regulator_disable;
> > +
> > + priv->vref_mv = ret / 1000;
> > + priv->use_internal_vref = false;
> > + } else {
> > + /* Use internal reference */
> > + priv->vref_mv = TI_TSC2046_INT_VREF;
> > + priv->use_internal_vref = true;
> > + }
> > +
>
> this part.
In this case we will not get any power saving, but instead we will need
to run enable/disable + regulator_get_voltage + extra calculation
without any advantage.
>
> > tsc2046_adc_parse_fwnode(priv);
> >
> > ret = tsc2046_adc_setup_spi_msg(priv);
> > if (ret)
> > - return ret;
> > + goto err_regulator_disable;
> >
> > mutex_init(&priv->slock);
> >
> > ret = devm_request_irq(dev, spi->irq, &tsc2046_adc_irq,
> > IRQF_NO_AUTOEN, indio_dev->name, indio_dev);
> > if (ret)
> > - return ret;
> > + goto err_regulator_disable;
> >
> > trig = devm_iio_trigger_alloc(dev, "touchscreen-%s", indio_dev->name);
> > - if (!trig)
> > - return -ENOMEM;
> > + if (!trig) {
> > + ret = -ENOMEM;
> > + goto err_regulator_disable;
> > + }
> >
> > priv->trig = trig;
> > iio_trigger_set_drvdata(trig, indio_dev);
> > @@ -811,20 +837,39 @@ static int tsc2046_adc_probe(struct spi_device *spi)
> > ret = devm_iio_trigger_register(dev, trig);
> > if (ret) {
> > dev_err(dev, "failed to register trigger\n");
> > - return ret;
> > + goto err_regulator_disable;
> > }
> >
> > ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> > &tsc2046_adc_trigger_handler, NULL);
> > if (ret) {
> > dev_err(dev, "Failed to setup triggered buffer\n");
> > - return ret;
> > + goto err_regulator_disable;
> > }
> >
> > /* set default trigger */
> > indio_dev->trig = iio_trigger_get(priv->trig);
> >
> > - return devm_iio_device_register(dev, indio_dev);
> > + ret = devm_iio_device_register(dev, indio_dev);
> > + if (ret)
> > + goto err_regulator_disable;
> > +
> > + return 0;
> > +
> > +err_regulator_disable:
> > + if (!IS_ERR(priv->vref_reg))
> > + regulator_disable(priv->vref_reg);
> > +
> > + return ret;
>
> As well as the whole new error handling and
>
> > +}
> > +
> > +static void tsc2046_adc_remove(struct spi_device *spi)
> > +{
> > + struct iio_dev *indio_dev = spi_get_drvdata(spi);
> > + struct tsc2046_adc_priv *priv = iio_priv(indio_dev);
> > +
> > + if (!IS_ERR(priv->vref_reg))
> > + regulator_disable(priv->vref_reg);
> > }
>
> the remove callback.
no.
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