Re: [PATCH v2 1/2] iio: adc: ti-ads7950: Allow to use on ACPI platforms

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 29 Jul 2017 20:27:13 -0500
David Lechner <david@lechnology.com> wrote:

> On 07/28/2017 05:20 PM, Andy Shevchenko wrote:
> > ACPI enabled platforms do not have a mean of regulators. Instead we use
> > hard coded voltage value for reference pin. When value is 0 (default) we
> > fall back to request a regulator.
> > 
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > ---
> >   drivers/iio/adc/ti-ads7950.c | 24 ++++++++++++++++++++----
> >   1 file changed, 20 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/ti-ads7950.c b/drivers/iio/adc/ti-ads7950.c
> > index 16a06633332c..ab669af291b7 100644
> > --- a/drivers/iio/adc/ti-ads7950.c
> > +++ b/drivers/iio/adc/ti-ads7950.c
> > @@ -21,6 +21,7 @@
> >    * GNU General Public License for more details.
> >    */
> >   
> > +#include <linux/acpi.h>
> >   #include <linux/bitops.h>
> >   #include <linux/device.h>
> >   #include <linux/err.h>
> > @@ -37,6 +38,12 @@
> >   #include <linux/iio/trigger_consumer.h>
> >   #include <linux/iio/triggered_buffer.h>
> >   
> > +/*
> > + * In case of ACPI, we use the 5000 mV as default for the reference pin.
> > + * Device tree users encode that via the vref-supply regulator.
> > + */
> > +#define TI_ADS7950_VA_MV_ACPI_DEFAULT	5000  
> 
> Now that I've thought about it a bit, you don't need to call this the 
> ACPI default, just call it the default. Then it will be obvious that 
> this is used when you don't have a regulator.
> 
> > +
> >   #define TI_ADS7950_CR_MANUAL	BIT(12)
> >   #define TI_ADS7950_CR_WRITE	BIT(11)
> >   #define TI_ADS7950_CR_CHAN(ch)	((ch) << 7)
> > @@ -58,6 +65,7 @@ struct ti_ads7950_state {
> >   	struct spi_message	scan_single_msg;
> >   
> >   	struct regulator	*reg;
> > +	unsigned int		vref_mv;
> >   
> >   	unsigned int		settings;
> >   
> > @@ -305,11 +313,15 @@ static int ti_ads7950_get_range(struct ti_ads7950_state *st)
> >   {
> >   	int vref;
> >   
> > -	vref = regulator_get_voltage(st->reg);
> > -	if (vref < 0)
> > -		return vref;
> > +	if (st->vref_mv) {
> > +		vref = st->vref_mv;
> > +	} else {
> > +		vref = regulator_get_voltage(st->reg);
> > +		if (vref < 0)
> > +			return vref;
> >   
> > -	vref /= 1000;
> > +		vref /= 1000;
> > +	}
> >   
> >   	if (st->settings & TI_ADS7950_CR_RANGE_5V)
> >   		vref *= 2;
> > @@ -411,6 +423,10 @@ static int ti_ads7950_probe(struct spi_device *spi)
> >   	spi_message_init_with_transfers(&st->scan_single_msg,
> >   					st->scan_single_xfer, 3);
> >   
> > +	/* Use hard coded value for reference voltage in ACPI case */
> > +	if (ACPI_COMPANION(&spi->dev))
> > +		st->vref_mv = TI_ADS7950_VA_MV_ACPI_DEFAULT;  
> 
> Instead of checking or ACPI, you could just say "if we have a dummy 
> regulator, then use the default value".
> 
Agreed. Sounds sensible to me.  Hopefully in DT people will
provide the right regulator, but chances are this won't
always happen.

Jonathan
> > +
> >   	st->reg = devm_regulator_get(&spi->dev, "vref");
> >   	if (IS_ERR(st->reg)) {
> >   		dev_err(&spi->dev, "Failed get get regulator \"vref\"\n");
> >   
>