Re: [PATCH v5 0/4] iio: chemical: Add support for Sensirion SCD4x CO2 sensor

[Roan van Dijk <roan@protonic.nl>]

On 14-10-2021 19:19, Jonathan Cameron wrote:
> On Thu, 14 Oct 2021 10:24:54 +0200
> Roan van Dijk <roan@protonic.nl> wrote:
> 
>> On 13-10-2021 19:38, Jonathan Cameron wrote:
>>> On Sun, 10 Oct 2021 16:59:19 +0100
>>> Jonathan Cameron <jic23@kernel.org> wrote:
>>>    
>>>> On Fri,  8 Oct 2021 12:17:02 +0200
>>>> Roan van Dijk <roan@protonic.nl> wrote:
>>>>   
>>>>> This series adds support for the Sensirion SCD4x sensor.
>>>>>
>>>>> The driver supports continuous reads of temperature, relative humdity and CO2
>>>>> concentration. There is an interval of 5 seconds between readings. During
>>>>> this interval the drivers checks if the sensor has new data available.
>>>>>
>>>>> The driver is based on the scd30 driver. However, The scd4x has become too
>>>>> different to just expand the scd30 driver. I made a new driver instead of
>>>>> expanding the scd30 driver. I hope I made the right choice by doing so?
>>>>
>>>> Applied to the togreg branch of iio.git with the issues Randy mentioned tidied
>>>> up. Pushed out as testing for 0-day to see if it can find anything we missed
>>>
>>> And indeed - I missed a bunch of places where explicit __be16 types should have
>>> been used.
>>>
>>> I've applied the following fixup, shout if it's wrong.
>>>   
>> Thank you Jonathan for applying this fixup. No need to shout :) Your
>> changes should fix the issue.
>>
>> However, I have a question about something else. The co2 concentration
>> is an IIO_CHAN_INFO_RAW, but doesn't have a scale or offset at this
>> moment. Is an _scale always required for an _raw in the ABI? I could not
>> find anything in the documentation if there is a rule for this. Someone
>> mentioned this to me, so I want to check if I did this right.
>>
>> The sensor returns the actual co2 value upon reading, like 450 ppm. We
>> can set an offset of this co2 value with the calibration_forced_value
>> through the ABI, but this offset is handled internally by the sensor. So
>> there isn't anything with scaling or an offset needed at the driver side.
> 
> Ah. We could have mapped this to calibbias, though here it's made more
> complex by other calibrations existing that don't use the value so let's
> leave it as it is.
> 
>>
>> Was I right by making it of type RAW? If needed we could make it more
>> like the scd30 driver, keeping it of type RAW but with scale = 1. What
>> should I do or is it fine as it is?
> 
> Hmm. Interesting corner case in the ABI.  A _raw value without a scale
> normally means we don't know it for some reason.  The most common case
> of this is light sensors where several _raw intensity values are combined
> in some (typically non linear) transform to form a single measure of illuminance.
> Those intensity_raw channels don't have an meaningful units, but devices
> often have threshold events on them so we have to expose them.
> 
> I would say make it a processed value, but there is a quirk.
> concentrations in IIO are expressed in percent not per million, so you need
> a scale anyway, I guess 10000?  See Documentation/ABI/testing/sysfs-bus-iio
> 
> 
> No need to do a new driver version, just send a patch tidying up this corner.
> 

Hi Jonathan,

As you suggested, these are my fixes for the concentration reading.

The co2 reading is now a processed value and has a scale. I also added 
the information in sysfs-bus-iio documentation, because this type of 
processed value is new in the ABI.

diff --git a/Documentation/ABI/testing/sysfs-bus-iio 
b/Documentation/ABI/testing/sysfs-bus-iio
index c27347d3608e..66a17f4c831e 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1716,6 +1716,7 @@ Description:

  What:          /sys/bus/iio/devices/iio:deviceX/in_concentration_raw
  What:          /sys/bus/iio/devices/iio:deviceX/in_concentrationX_raw
+What:          /sys/bus/iio/devices/iio:deviceX/in_concentration_co2_input
  What:          /sys/bus/iio/devices/iio:deviceX/in_concentration_co2_raw
  What:          /sys/bus/iio/devices/iio:deviceX/in_concentrationX_co2_raw
  What: 
/sys/bus/iio/devices/iio:deviceX/in_concentration_ethanol_raw
diff --git a/drivers/iio/chemical/scd4x.c b/drivers/iio/chemical/scd4x.c
index 09b34201c42b..bc1c6676029d 100644
--- a/drivers/iio/chemical/scd4x.c
+++ b/drivers/iio/chemical/scd4x.c
@@ -337,6 +337,7 @@ static int scd4x_read_raw(struct iio_dev *indio_dev,

         switch (mask) {
         case IIO_CHAN_INFO_RAW:
+       case IIO_CHAN_INFO_PROCESSED:
                 ret = iio_device_claim_direct_mode(indio_dev);
                 if (ret)
                         return ret;
@@ -352,7 +353,11 @@ static int scd4x_read_raw(struct iio_dev *indio_dev,
                 *val = ret;
                 return IIO_VAL_INT;
         case IIO_CHAN_INFO_SCALE:
-               if (chan->type == IIO_TEMP) {
+               if (chan->type == IIO_CONCENTRATION) {
+                       *val = 0;
+                       *val2 = 100;
+                       return IIO_VAL_INT_PLUS_MICRO;
+               } else if (chan->type == IIO_TEMP) {
                         *val = 175000;
                         *val2 = 65536;
                         return IIO_VAL_FRACTIONAL;
@@ -501,7 +506,8 @@ static const struct iio_chan_spec scd4x_channels[] = {
                 .type = IIO_CONCENTRATION,
                 .channel2 = IIO_MOD_CO2,
                 .modified = 1,
-               .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+               .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
+                                       BIT(IIO_CHAN_INFO_SCALE),
                 .address = SCD4X_CO2,
                 .scan_index = SCD4X_CO2,
                 .scan_type = {

Thanks,

Roan

> Thanks,
> 
> Jonathan
> 
> 
>> Sorry for not asking this earlier.
>>
>> Thanks,
>>
>> Roan
>>
>>> diff --git a/drivers/iio/chemical/scd4x.c b/drivers/iio/chemical/scd4x.c
>>> index 09b34201c42b..ebebcb117ba2 100644
>>> --- a/drivers/iio/chemical/scd4x.c
>>> +++ b/drivers/iio/chemical/scd4x.c
>>> @@ -263,7 +263,7 @@ static int scd4x_write_and_fetch(struct scd4x_state *state, enum scd4x_cmd cmd,
>>>    static int scd4x_read_meas(struct scd4x_state *state, uint16_t *meas)
>>>    {
>>>    	int i, ret;
>>> -	uint16_t buf[3];
>>> +	__be16 buf[3];
>>>    
>>>    	ret = scd4x_read(state, CMD_READ_MEAS, buf, sizeof(buf));
>>>    	if (ret)
>>> @@ -282,12 +282,13 @@ static int scd4x_wait_meas_poll(struct scd4x_state *state)
>>>    	int ret;
>>>    
>>>    	do {
>>> +		__be16 bval;
>>>    		uint16_t val;
>>>    
>>> -		ret = scd4x_read(state, CMD_GET_DATA_READY, &val, sizeof(val));
>>> +		ret = scd4x_read(state, CMD_GET_DATA_READY, &bval, sizeof(bval));
>>>    		if (ret)
>>>    			return -EIO;
>>> -		val = be16_to_cpu(val);
>>> +		val = be16_to_cpu(bval);
>>>    
>>>    		/* new measurement available */
>>>    		if (val & 0x7FF)
>>> @@ -333,7 +334,7 @@ static int scd4x_read_raw(struct iio_dev *indio_dev,
>>>    {
>>>    	struct scd4x_state *state = iio_priv(indio_dev);
>>>    	int ret;
>>> -	uint16_t tmp;
>>> +	__be16 tmp;
>>>    
>>>    	switch (mask) {
>>>    	case IIO_CHAN_INFO_RAW:
>>> @@ -405,17 +406,18 @@ static ssize_t calibration_auto_enable_show(struct device *dev,
>>>    	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>>>    	struct scd4x_state *state = iio_priv(indio_dev);
>>>    	int ret;
>>> -	uint16_t val;
>>> +	__be16 bval;
>>> +	u16 val;
>>>    
>>>    	mutex_lock(&state->lock);
>>> -	ret = scd4x_read(state, CMD_GET_ASC, &val, sizeof(val));
>>> +	ret = scd4x_read(state, CMD_GET_ASC, &bval, sizeof(bval));
>>>    	mutex_unlock(&state->lock);
>>>    	if (ret) {
>>>    		dev_err(dev, "failed to read automatic calibration");
>>>    		return ret;
>>>    	}
>>>    
>>> -	val = (be16_to_cpu(val) & SCD4X_READY_MASK) ? 1 : 0;
>>> +	val = (be16_to_cpu(bval) & SCD4X_READY_MASK) ? 1 : 0;
>>>    
>>>    	return sprintf(buf, "%d\n", val);
>>>    }
>>>
>>>    
>>>>
>>>> Thanks,
>>>>
>>>> Jonathan
>>>>   
>>>>>
>>>>> Changes since v5:
>>>>> scd4x.c:
>>>>>     - Fix bug in trigger_handler
>>>>>
>>>>> Changes since v4:
>>>>> scd4x.c:
>>>>>     - Minor fixes in documentation
>>>>>     - Reorder trigger_handler so memcpy is not needed anymore
>>>>> Documentation:
>>>>>     - Change information about the KernelVersion for the
>>>>>       calibration_forced_value_available
>>>>>
>>>>> Changes since v3:
>>>>> scd4x.c
>>>>>     - Change read and write_and_fetch function parameter. CRC byte is now
>>>>>       hidden inside the function.
>>>>>     - Fix minor style issues
>>>>>     - Add calibration_forced_value_available attribute to the driver
>>>>>     - Remove including BUFFER_TRIGGERED
>>>>>     - Change calibbias to raw ADC readings rather than converting it to
>>>>>       milli degrees C.
>>>>> Documentation:
>>>>>     - Change description of driver attributes
>>>>>     - Add calibration_forced_value_available documentation
>>>>>
>>>>> Changes since v2:
>>>>> scd4x.c:
>>>>>     - Change boolean operations
>>>>>     - Document scope of lock
>>>>>     - Remove device *dev from struct
>>>>>     - Add goto block for errror handling
>>>>>     - Add function to read value per channel in read_raw
>>>>>     - Fix bug with lock in error paths
>>>>>     - Remove conversion of humidity and temperature values
>>>>>     - Add scale and offset to temperature channel
>>>>>     - Add scale to humidity channel
>>>>>     - Move memset out of locked section
>>>>>     - Remove unused irq functions
>>>>>     - Move device register at end of probe function
>>>>> Documentation:
>>>>>     - Copy content of sysfs-bus-iio-scd30 to sysfs-bus-iio
>>>>>     - Remove Documentation/ABI/testing/sysfs-bus-iio-scd30
>>>>>
>>>>> Changes since v1:
>>>>> dt-bindings:
>>>>>     - Separated compatible string for each sensor type
>>>>> scd4x.c:
>>>>>     - Changed probe, resume and suspend functions to static
>>>>>     - Added SIMPLE_DEV_PM_OPS function call for power management
>>>>>       operations.
>>>>>
>>>>> Roan van Dijk (4):
>>>>>     dt-bindings: iio: chemical: sensirion,scd4x: Add yaml description
>>>>>     MAINTAINERS: Add myself as maintainer of the scd4x driver
>>>>>     drivers: iio: chemical: Add support for Sensirion SCD4x CO2 sensor
>>>>>     iio: documentation: Document scd4x calibration use
>>>>>
>>>>>    Documentation/ABI/testing/sysfs-bus-iio       |  41 ++
>>>>>    Documentation/ABI/testing/sysfs-bus-iio-scd30 |  34 -
>>>>>    .../iio/chemical/sensirion,scd4x.yaml         |  46 ++
>>>>>    MAINTAINERS                                   |   6 +
>>>>>    drivers/iio/chemical/Kconfig                  |  13 +
>>>>>    drivers/iio/chemical/Makefile                 |   1 +
>>>>>    drivers/iio/chemical/scd4x.c                  | 689 ++++++++++++++++++
>>>>>    7 files changed, 796 insertions(+), 34 deletions(-)
>>>>>    delete mode 100644 Documentation/ABI/testing/sysfs-bus-iio-scd30
>>>>>    create mode 100644 Documentation/devicetree/bindings/iio/chemical/sensirion,scd4x.yaml
>>>>>    create mode 100644 drivers/iio/chemical/scd4x.c
>>>>>       
>>>>   
>>>    
>