linux-kernel - Re: [PATCH 3/4] iio: adc: Add support for the GE HealthCare PMC ADC

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Message-ID: <20241002102324.2e3600ca@bootlin.com>
Date: Wed, 2 Oct 2024 10:23:24 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, Luca Ceresoli
 <luca.ceresoli@...tlin.com>, Ian Ray <ian.ray@...ealthcare.com>, Thomas
 Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 3/4] iio: adc: Add support for the GE HealthCare PMC ADC

Hi Jonathan,

On Tue, 1 Oct 2024 20:24:30 +0100
Jonathan Cameron <jic23@...nel.org> wrote:

> On Tue,  1 Oct 2024 09:46:17 +0200
> Herve Codina <herve.codina@...tlin.com> wrote:
> 
> > The GE HealthCare PMC Analog to Digital Converter (ADC) is a 16-Channel
> > (voltage and current), 16-Bit ADC with an I2C Interface.
> > 
> > Signed-off-by: Herve Codina <herve.codina@...tlin.com>  
> 
> Just one thing to add to David's review.
> 
> I'm going to guess this isn't a general purpose ADC? Can you share any info
> on what sort of device it is used in?
> 
> No problem if not - I'm just curious as I've not seen GE HealthCare I2C parts
> before!

I cannot tell about the product it is used in :(
One sure thing I can say is that the component itself is not available off
the shelf, and is fully designed to be used in a specific product.

> 
> > diff --git a/drivers/iio/adc/gehc-pmc-adc.c b/drivers/iio/adc/gehc-pmc-adc.c
> > new file mode 100644
> > index 000000000000..c46c2fb84d35
> > --- /dev/null
> > +++ b/drivers/iio/adc/gehc-pmc-adc.c
> > @@ -0,0 +1,233 @@  
> 
> 
> > +
> > +static int pmc_adc_read_raw(struct iio_dev *indio_dev, struct iio_chan_spec const *chan,
> > +			    int *val, int *val2, long mask)
> > +{
> > +	struct pmc_adc *pmc_adc = iio_priv(indio_dev);
> > +	int ret;
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_RAW:
> > +		ret = pmc_adc_read_raw_ch(pmc_adc, chan->address, val);
> > +		if (ret)
> > +			return ret;
> > +		return IIO_VAL_INT;
> > +
> > +	case IIO_CHAN_INFO_SCALE:
> > +		*val = 1; /* Raw values are directly read in mV or mA */  
> 
> Drop this scale and make the channels processed. That saves userspace even applying

I thought that scale was mandatory.

From the userspace, offset is clearly optional
  https://elixir.bootlin.com/linux/v6.11/source/Documentation/ABI/testing/sysfs-bus-iio#L458
But nothing about a default value is mentioned in the scale description
  https://elixir.bootlin.com/linux/v6.11/source/Documentation/ABI/testing/sysfs-bus-iio#L515

> the *1 this indicates.  Rare to find a device that outputs in our base units
> but might as well take advantage of one that does :)

Yes, the device is a custom designed device and it has a fully knowledge (by
design) of the board it is soldered on. As I was involved in the communication
protocol definition, units were chosen to fit well with IIO.

> 
> > +		return IIO_VAL_INT;
> > +	}
> > +
> > +	return -EINVAL;
> > +}  

Best regards,
Hervé