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Date:   Sun, 31 Jan 2021 13:11:41 +0000
From:   Jonathan Cameron <jic23@kernel.org>
To:     Jyoti Bhayana <jbhayana@google.com>
Cc:     Hartmut Knaack <knaack.h@gmx.de>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
        cristian.marussi@arm.com, sudeep.holla@arm.com,
        egranata@google.com, mikhail.golubev@opensynergy.com,
        Igor.Skalkin@opensynergy.com, Peter.hilber@opensynergy.com,
        ankitarora@google.com
Subject: Re: [RFC PATCH v4 1/1] iio/scmi: Adding support for IIO SCMI Based
 Sensors
Message-ID: <20210131131141.468f1cc2@archlinux>
In-Reply-To: <20210129221818.3540620-2-jbhayana@google.com>
References: <20210129221818.3540620-1-jbhayana@google.com>
        <20210129221818.3540620-2-jbhayana@google.com>
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On Fri, 29 Jan 2021 22:18:18 +0000
Jyoti Bhayana <jbhayana@google.com> wrote:

> This change provides ARM SCMI Protocol based IIO device.
> This driver provides support for Accelerometer and Gyroscope using
> SCMI Sensor Protocol extensions added in the SCMIv3.0 ARM specification
> 
> Signed-off-by: Jyoti Bhayana <jbhayana@google.com>

A few minor things noticed on a fresh read through, but mostly I think
we are down to figuring out how to deal with the range (as discussed
in the thread continuing on v3).

On another note, probably time to drop the RFC or give a bit more detail
on why you think this isn't ready to be applied.

Thanks,

Jonathan

> ---
>  MAINTAINERS                                |   6 +
>  drivers/iio/common/Kconfig                 |   1 +
>  drivers/iio/common/Makefile                |   1 +
>  drivers/iio/common/scmi_sensors/Kconfig    |  18 +
>  drivers/iio/common/scmi_sensors/Makefile   |   5 +
>  drivers/iio/common/scmi_sensors/scmi_iio.c | 742 +++++++++++++++++++++
>  6 files changed, 773 insertions(+)
>  create mode 100644 drivers/iio/common/scmi_sensors/Kconfig
>  create mode 100644 drivers/iio/common/scmi_sensors/Makefile
>  create mode 100644 drivers/iio/common/scmi_sensors/scmi_iio.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index b516bb34a8d5..ccf37d43ab41 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8567,6 +8567,12 @@ S:	Maintained
>  F:	Documentation/devicetree/bindings/iio/multiplexer/io-channel-mux.txt
>  F:	drivers/iio/multiplexer/iio-mux.c
>  
> +IIO SCMI BASED DRIVER
> +M:	Jyoti Bhayana <jbhayana@google.com>
> +L:	linux-iio@vger.kernel.org
> +S:	Maintained
> +F:	drivers/iio/common/scmi_sensors/scmi_iio.c
> +
>  IIO SUBSYSTEM AND DRIVERS
>  M:	Jonathan Cameron <jic23@kernel.org>
>  R:	Lars-Peter Clausen <lars@metafoo.de>
> diff --git a/drivers/iio/common/Kconfig b/drivers/iio/common/Kconfig
> index 2b9ee9161abd..0334b4954773 100644
> --- a/drivers/iio/common/Kconfig
> +++ b/drivers/iio/common/Kconfig
> @@ -6,5 +6,6 @@
>  source "drivers/iio/common/cros_ec_sensors/Kconfig"
>  source "drivers/iio/common/hid-sensors/Kconfig"
>  source "drivers/iio/common/ms_sensors/Kconfig"
> +source "drivers/iio/common/scmi_sensors/Kconfig"
>  source "drivers/iio/common/ssp_sensors/Kconfig"
>  source "drivers/iio/common/st_sensors/Kconfig"
> diff --git a/drivers/iio/common/Makefile b/drivers/iio/common/Makefile
> index 4bc30bb548e2..fad40e1e1718 100644
> --- a/drivers/iio/common/Makefile
> +++ b/drivers/iio/common/Makefile
> @@ -11,5 +11,6 @@
>  obj-y += cros_ec_sensors/
>  obj-y += hid-sensors/
>  obj-y += ms_sensors/
> +obj-y += scmi_sensors/
>  obj-y += ssp_sensors/
>  obj-y += st_sensors/
> diff --git a/drivers/iio/common/scmi_sensors/Kconfig b/drivers/iio/common/scmi_sensors/Kconfig
> new file mode 100644
> index 000000000000..67e084cbb1ab
> --- /dev/null
> +++ b/drivers/iio/common/scmi_sensors/Kconfig
> @@ -0,0 +1,18 @@
> +#
> +# IIO over SCMI
> +#
> +# When adding new entries keep the list in alphabetical order
> +
> +menu "IIO SCMI Sensors"
> +
> +config IIO_SCMI
> +	tristate "IIO SCMI"
> +        depends on ARM_SCMI_PROTOCOL
> +        select IIO_BUFFER
> +        select IIO_KFIFO_BUF
> +	help
> +          Say yes here to build support for IIO SCMI Driver.
> +          This provides ARM SCMI Protocol based IIO device.
> +          This driver provides support for accelerometer and gyroscope
> +          sensors available on SCMI based platforms.
> +endmenu
> diff --git a/drivers/iio/common/scmi_sensors/Makefile b/drivers/iio/common/scmi_sensors/Makefile
> new file mode 100644
> index 000000000000..f13140a2575a
> --- /dev/null
> +++ b/drivers/iio/common/scmi_sensors/Makefile
> @@ -0,0 +1,5 @@
> +# SPDX - License - Identifier : GPL - 2.0 - only
> +#
> +# Makefile for the IIO over SCMI
> +#
> +obj-$(CONFIG_IIO_SCMI) += scmi_iio.o
> diff --git a/drivers/iio/common/scmi_sensors/scmi_iio.c b/drivers/iio/common/scmi_sensors/scmi_iio.c
> new file mode 100644
> index 000000000000..331ffaffd06f
> --- /dev/null
> +++ b/drivers/iio/common/scmi_sensors/scmi_iio.c
> @@ -0,0 +1,742 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * System Control and Management Interface(SCMI) based IIO sensor driver
> + *
> + * Copyright (C) 2020 Google LLC
Probably want to include 2021 given you are still making substantial changes ;)

> + */
> +
> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/kfifo_buf.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/kernel.h>
> +#include <linux/kthread.h>
> +#include <linux/module.h>
> +#include <linux/scmi_protocol.h>
> +#include <linux/time.h>
> +#include <linux/types.h>
> +
> +#define ilog10(x) (ilog2(x) / const_ilog2(10))

That feels like it's probably not great for precision.

> +#define UHZ_PER_HZ 1000000UL
> +#define ODR_EXPAND(odr, uodr) (((odr) * 1000000ULL) + (uodr))

Prefix these if driver specific.
For those that aren't perhaps we can think about putting them in
generic headers.


> +#define MAX_NUM_OF_CHANNELS 4
> +#define H32(x) (FIELD_GET(GENMASK_ULL(63, 32), (x)))
> +#define L32(x) (FIELD_GET(GENMASK_ULL(31, 0), (x)))

Can we use upper_32_bits() etc in stead of these?

> +
> +struct scmi_iio_priv {
> +	struct scmi_handle *handle;
> +	const struct scmi_sensor_info *sensor_info;
> +	struct iio_dev *indio_dev;
> +	long long iio_buf[MAX_NUM_OF_CHANNELS];
> +	struct notifier_block sensor_update_nb;
> +	u32 *freq_avail;
> +	/*
> +	 * range_avail = [minRange resolution maxRange]
> +	 * with IIO val type as IIO_VAL_FRACTIONAL.
> +	 * Hence, array of size 6.
> +	 */
> +	int range_avail[6];
> +};
> +
> +static int scmi_iio_sensor_update_cb(struct notifier_block *nb,
> +				     unsigned long event, void *data)
> +{
> +	struct scmi_sensor_update_report *sensor_update = data;
> +	struct iio_dev *scmi_iio_dev;
> +	struct scmi_iio_priv *sensor;
> +	s8 tstamp_scale;
> +	u64 time, time_ns;
> +	int i;
> +
> +	if (sensor_update->readings_count == 0)
> +		return NOTIFY_DONE;
> +
> +	sensor = container_of(nb, struct scmi_iio_priv, sensor_update_nb);
> +
> +	for (i = 0; i < sensor_update->readings_count; i++)
> +		sensor->iio_buf[i] = sensor_update->readings[i].value;
> +
> +	if (!sensor->sensor_info->timestamped) {
> +		time_ns = sensor_update->timestamp;
> +	} else {
> +		/*
> +		 * All the axes are supposed to have the same value for timestamp.
> +		 *  We are just using the values from the Axis 0 here.

Slightly odd indenting of comment here.

> +		 */
> +		time = sensor_update->readings[0].timestamp;
> +
> +		/*
> +		 *  Timestamp returned by SCMI is in seconds and is equal to
> +		 *  time * power-of-10 multiplier(tstamp_scale) seconds.
> +		 *  Converting the timestamp to nanoseconds below.
> +		 */
> +		tstamp_scale = sensor->sensor_info->tstamp_scale +
> +				  ilog10(NSEC_PER_SEC);
> +		if (tstamp_scale < 0)
> +			time_ns = div64_u64(time,
> +					    int_pow(10, abs(tstamp_scale)));
> +		else
> +			time_ns = time * int_pow(10, tstamp_scale);
> +	}
> +
> +	scmi_iio_dev = sensor->indio_dev;
> +	iio_push_to_buffers_with_timestamp(scmi_iio_dev, sensor->iio_buf,
> +					   time_ns);
> +	return NOTIFY_OK;
> +}
> +
> +static int scmi_iio_buffer_preenable(struct iio_dev *iio_dev)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	u32 sensor_id = sensor->sensor_info->id;
> +	u32 sensor_config;
> +	int err;
> +
> +	if (sensor->sensor_info->timestamped)
> +		sensor_config |= FIELD_PREP(SCMI_SENS_CFG_TSTAMP_ENABLED_MASK,
> +					    SCMI_SENS_CFG_TSTAMP_ENABLE);
> +
> +	sensor_config |= FIELD_PREP(SCMI_SENS_CFG_SENSOR_ENABLED_MASK,
> +				    SCMI_SENS_CFG_SENSOR_ENABLE);
> +
> +	err = sensor->handle->notify_ops->register_event_notifier(sensor->handle,
> +			SCMI_PROTOCOL_SENSOR, SCMI_EVENT_SENSOR_UPDATE,
> +			&sensor_id, &sensor->sensor_update_nb);
> +	if (err) {
> +		dev_err(&iio_dev->dev,
> +			"Error in registering sensor update notifier for sensor %s err %d",
> +			sensor->sensor_info->name, err);
> +		return err;
> +	}
> +
> +	err = sensor->handle->sensor_ops->config_set(sensor->handle,
> +			sensor->sensor_info->id, sensor_config);
> +	if (err) {
> +		sensor->handle->notify_ops->unregister_event_notifier(sensor->handle,
> +			SCMI_PROTOCOL_SENSOR, SCMI_EVENT_SENSOR_UPDATE,
> +			&sensor_id, &sensor->sensor_update_nb);
> +		dev_err(&iio_dev->dev, "Error in enabling sensor %s err %d",
> +			sensor->sensor_info->name, err);
> +	}
> +
> +	return err;
> +}
> +
> +static int scmi_iio_buffer_postdisable(struct iio_dev *iio_dev)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	u32 sensor_id = sensor->sensor_info->id;
> +	u32 sensor_config = 0;
> +	int err;
> +
> +	sensor_config |= FIELD_PREP(SCMI_SENS_CFG_SENSOR_ENABLED_MASK,
> +				    SCMI_SENS_CFG_SENSOR_DISABLE);
> +
> +	err = sensor->handle->notify_ops->unregister_event_notifier(sensor->handle,
> +			SCMI_PROTOCOL_SENSOR, SCMI_EVENT_SENSOR_UPDATE,
> +			&sensor_id, &sensor->sensor_update_nb);
> +	if (err) {
> +		dev_err(&iio_dev->dev,
> +			"Error in unregistering sensor update notifier for sensor %s err %d",
> +			sensor->sensor_info->name, err);
> +		return err;
> +	}
> +
> +	err = sensor->handle->sensor_ops->config_set(sensor->handle, sensor_id,
> +						     sensor_config);
> +	if (err) {
> +		dev_err(&iio_dev->dev,
> +			"Error in disabling sensor %s with err %d",
> +			sensor->sensor_info->name, err);
> +	}
> +
> +	return err;
> +}
> +
> +static const struct iio_buffer_setup_ops scmi_iio_buffer_ops = {
> +	.preenable = scmi_iio_buffer_preenable,
> +	.postdisable = scmi_iio_buffer_postdisable,
> +};
> +
> +static int scmi_iio_read_avail(struct iio_dev *iio_dev,
> +			       struct iio_chan_spec const *chan,
> +			       const int **vals, int *type, int *length,
> +			       long mask)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		*vals = sensor->freq_avail;
> +		*type = IIO_VAL_INT_PLUS_MICRO;
> +		*length = sensor->sensor_info->intervals.count * 2;
> +		if (sensor->sensor_info->intervals.segmented)
> +			return IIO_AVAIL_RANGE;
> +		else
> +			return IIO_AVAIL_LIST;
> +	case IIO_CHAN_INFO_RAW:
> +		*vals = sensor->range_avail;
> +		*type = IIO_VAL_FRACTIONAL;
> +		*length = ARRAY_SIZE(sensor->range_avail);
> +		return IIO_AVAIL_RANGE;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int scmi_iio_set_odr_val(struct iio_dev *iio_dev, int val, int val2)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	u64 sec, mult, uHz;
> +	u32 sensor_config;
> +
> +	int err = sensor->handle->sensor_ops->config_get(sensor->handle,
> +			sensor->sensor_info->id, &sensor_config);
> +	if (err) {
> +		dev_err(&iio_dev->dev,
> +			"Error in getting sensor config for sensor %s err %d",
> +			sensor->sensor_info->name, err);
> +		return err;
> +	}
> +
> +	uHz = ODR_EXPAND(val, val2);
> +
> +	/*
> +	 * The seconds field in the sensor interval in SCMI is 16 bits long
> +	 * Therefore seconds  = 1/Hz <= 0xFFFF. As floating point calculations are
> +	 * discouraged in the kernel driver code, to calculate the scale factor (sf)
> +	 * (1* 1000000 * sf)/uHz <= 0xFFFF. Therefore, sf <= (uHz * 0xFFFF)/1000000
> +	 */
> +	mult = ilog10(((u64)uHz * 0xFFFF) / UHZ_PER_HZ);
> +
> +	sec = div64_u64(int_pow(10, mult) * UHZ_PER_HZ, uHz);
> +	if (sec == 0) {
> +		dev_err(&iio_dev->dev,
> +			"Trying to set invalid sensor update value for sensor %s",
> +			sensor->sensor_info->name);
> +		return -EINVAL;
> +	}
> +
> +	sensor_config &= ~SCMI_SENS_CFG_UPDATE_SECS_MASK;
> +	sensor_config |= FIELD_PREP(SCMI_SENS_CFG_UPDATE_SECS_MASK, sec);
> +	sensor_config &= ~SCMI_SENS_CFG_UPDATE_EXP_MASK;
> +	sensor_config |= FIELD_PREP(SCMI_SENS_CFG_UPDATE_EXP_MASK, -mult);
> +
> +	if (sensor->sensor_info->timestamped) {
> +		sensor_config &= ~SCMI_SENS_CFG_TSTAMP_ENABLED_MASK;
> +		sensor_config |= FIELD_PREP(SCMI_SENS_CFG_TSTAMP_ENABLED_MASK,
> +					    SCMI_SENS_CFG_TSTAMP_ENABLE);
> +	}
> +
> +	sensor_config &= ~SCMI_SENS_CFG_ROUND_MASK;
> +	sensor_config |=
> +		FIELD_PREP(SCMI_SENS_CFG_ROUND_MASK, SCMI_SENS_CFG_ROUND_AUTO);
> +
> +	err = sensor->handle->sensor_ops->config_set(sensor->handle,
> +			sensor->sensor_info->id, sensor_config);
> +	if (err)
> +		dev_err(&iio_dev->dev,
> +			"Error in setting sensor update interval for sensor %s value %u err %d",
> +			sensor->sensor_info->name, sensor_config, err);
> +
> +	return err;
> +}
> +
> +static int scmi_iio_write_raw(struct iio_dev *iio_dev,
> +			      struct iio_chan_spec const *chan, int val,
> +			      int val2, long mask)
> +{
> +	int err;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		mutex_lock(&iio_dev->mlock);
> +		err = scmi_iio_set_odr_val(iio_dev, val, val2);
> +		mutex_unlock(&iio_dev->mlock);
> +		return err;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static u64 scmi_iio_convert_interval_to_ns(u32 val)
> +{
> +	u64 sensor_update_interval =
> +		SCMI_SENS_INTVL_GET_SECS(val) * NSEC_PER_SEC;
> +	u64 sensor_interval_mult;
> +	int mult;
> +
> +	mult = SCMI_SENS_INTVL_GET_EXP(val);
> +	if (mult < 0) {
> +		sensor_interval_mult = int_pow(10, abs(mult));
> +		sensor_update_interval =
> +			sensor_update_interval / sensor_interval_mult;
> +	} else {
> +		sensor_interval_mult = int_pow(10, mult);
> +		sensor_update_interval =
> +			sensor_update_interval * sensor_interval_mult;
> +	}
> +	return sensor_update_interval;
> +}
> +
> +static void convert_ns_to_freq(u64 interval_ns, u64 *hz, u64 *uhz)
> +{
> +	u64 rem;
> +
> +	*hz = div64_u64_rem(NSEC_PER_SEC, interval_ns, &rem);
> +	*uhz = (rem * 1000000UL) / interval_ns;
> +}
> +
> +static int scmi_iio_get_odr_val(struct iio_dev *iio_dev, int *val, int *val2)
> +{
> +	u64 sensor_update_interval, sensor_interval_mult, hz, uhz;
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	u32 sensor_config;
> +	int mult;
> +
> +	int err = sensor->handle->sensor_ops->config_get(sensor->handle,
> +			sensor->sensor_info->id, &sensor_config);
> +	if (err) {
> +		dev_err(&iio_dev->dev,
> +			"Error in getting sensor config for sensor %s err %d",
> +			sensor->sensor_info->name, err);
> +		return err;
> +	}
> +
> +	sensor_update_interval =
> +		SCMI_SENS_CFG_GET_UPDATE_SECS(sensor_config) * NSEC_PER_SEC;
> +
> +	mult = SCMI_SENS_CFG_GET_UPDATE_EXP(sensor_config);
> +	if (mult < 0) {
> +		sensor_interval_mult = int_pow(10, abs(mult));
> +		sensor_update_interval =
> +			sensor_update_interval / sensor_interval_mult;
> +	} else {
> +		sensor_interval_mult = int_pow(10, mult);
> +		sensor_update_interval =
> +			sensor_update_interval * sensor_interval_mult;
> +	}
> +
> +	convert_ns_to_freq(sensor_update_interval, &hz, &uhz);
> +	*val = hz;
> +	*val2 = uhz;
> +	return 0;
> +}
> +
> +static int scmi_iio_read_raw(struct iio_dev *iio_dev,
> +			     struct iio_chan_spec const *ch, int *val,
> +			     int *val2, long mask)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	s8 scale;
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SCALE:
> +		scale = sensor->sensor_info->axis[ch->scan_index].scale;
> +		if (scale < 0) {
> +			*val = 1;
> +			*val2 = int_pow(10, abs(scale));
> +			return IIO_VAL_FRACTIONAL;
> +		}
> +		*val = int_pow(10, scale);
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		ret = scmi_iio_get_odr_val(iio_dev, val, val2);
> +		return ret ? ret : IIO_VAL_INT_PLUS_MICRO;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info scmi_iio_info = {
> +	.read_raw = scmi_iio_read_raw,
> +	.read_avail = scmi_iio_read_avail,
> +	.write_raw = scmi_iio_write_raw,
> +};
> +
> +static void scmi_iio_set_timestamp_channel(struct iio_chan_spec *iio_chan,
> +					   int scan_index)
> +{
> +	iio_chan->type = IIO_TIMESTAMP;
> +	iio_chan->channel = -1;
> +	iio_chan->scan_index = scan_index;
> +	iio_chan->scan_type.sign = 'u';
> +	iio_chan->scan_type.realbits = 64;
> +	iio_chan->scan_type.storagebits = 64;
> +}
> +
> +static void scmi_iio_set_data_channel(struct iio_chan_spec *iio_chan,
> +				      enum iio_chan_type type,
> +				      enum iio_modifier mod, int scan_index)
> +{
> +	iio_chan->type = type;
> +	iio_chan->modified = 1;
> +	iio_chan->channel2 = mod;
> +	iio_chan->info_mask_separate = BIT(IIO_CHAN_INFO_SCALE);
> +	iio_chan->info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SAMP_FREQ);
> +	iio_chan->info_mask_shared_by_type_available =
> +		BIT(IIO_CHAN_INFO_SAMP_FREQ) | BIT(IIO_CHAN_INFO_RAW);
> +	iio_chan->scan_index = scan_index;
> +	iio_chan->scan_type.sign = 's';
> +	iio_chan->scan_type.realbits = 64;
> +	iio_chan->scan_type.storagebits = 64;
> +	iio_chan->scan_type.endianness = IIO_LE;
> +}
> +
> +static int scmi_iio_get_chan_modifier(const char *name,
> +				      enum iio_modifier *modifier)
> +{
> +	char *pch, mod;
> +
> +	if (!name)
> +		return -EINVAL;
> +
> +	pch = strrchr(name, '_');
> +	if (!pch)
> +		return -EINVAL;
> +
> +	mod = *(pch + 1);
> +	switch (mod) {
> +	case 'X':
> +		*modifier = IIO_MOD_X;
> +		return 0;
> +	case 'Y':
> +		*modifier = IIO_MOD_Y;
> +		return 0;
> +	case 'Z':
> +		*modifier = IIO_MOD_Z;
> +		return 0;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int scmi_iio_get_chan_type(u8 scmi_type, enum iio_chan_type *iio_type)
> +{
> +	switch (scmi_type) {
> +	case METERS_SEC_SQUARED:
> +		*iio_type = IIO_ACCEL;
> +		return 0;
> +	case RADIANS_SEC:
> +		*iio_type = IIO_ANGL_VEL;
> +		return 0;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int scmi_iio_get_sensor_max_range(struct iio_dev *iio_dev, int *val,
> +					 int *val2)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	int max_range_high, max_range_low;
> +	long long max_range;
> +
> +	/*
> +	 * All the axes are supposed to have the same value for max range.
> +	 * We are just using the values from the Axis 0 here.
> +	 */
> +	if (sensor->sensor_info->axis[0].extended_attrs) {
> +		max_range = sensor->sensor_info->axis[0].attrs.max_range;
> +		max_range_high = H32(max_range);
> +		max_range_low = L32(max_range);
> +
> +		/*
> +		 * As IIO Val types have no provision for 64 bit values,
> +		 * this driver only supports sensors whose maximum range
> +		 * reported by the SCMI Platform fits within lower 32 bits
> +		 */
> +		if (max_range_high != 0)
> +			return -EINVAL;
> +
> +		*val = max_range_low;
> +		*val2 = 1;
> +	}
> +	return 0;
> +}
> +
> +static void scmi_iio_get_sensor_resolution(struct iio_dev *iio_dev, int *val,
> +					   int *val2)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +
> +	/*
> +	 * All the axes are supposed to have the same value for resolution
> +	 * and exponent. We are just using the values from the Axis 0 here.
> +	 */
> +	if (sensor->sensor_info->axis[0].extended_attrs) {
> +		uint resolution = sensor->sensor_info->axis[0].resolution;
> +		s8 exponent = sensor->sensor_info->axis[0].exponent;
> +		s8 scale = sensor->sensor_info->axis[0].scale;
> +
> +		/*
> +		 * To provide the raw value for the resolution to the userspace,
> +		 * need to divide the resolution exponent by the sensor scale
> +		 */
> +		exponent = exponent - scale;
> +		if (exponent >= 0) {
> +			*val = resolution * int_pow(10, exponent);
> +			*val2 = 1;
> +		} else {
> +			*val = resolution;
> +			*val2 = int_pow(10, abs(exponent));
> +		}
> +	}
> +}
> +
> +static int scmi_iio_get_sensor_min_range(struct iio_dev *iio_dev, int *val,
> +					 int *val2)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	int min_range_high, min_range_low;
> +	long long min_range;
> +
> +	/*
> +	 * All the axes are supposed to have the same value for min range.
> +	 * We are just using the values from the Axis 0 here.
> +	 */
> +	if (sensor->sensor_info->axis[0].extended_attrs) {
> +		min_range = sensor->sensor_info->axis[0].attrs.min_range;
> +		min_range_high = H32(min_range);
> +		min_range_low = L32(min_range);
> +
> +		/*
> +		 * As IIO Val types have no provision for 64 bit values,
> +		 * this driver only supports sensors whose minimum range
> +		 * reported by SCMI Platform fits within lower 32 bits
> +		 */

As discussed in previous thread (after you sent this!) perhaps we just
need to do the maths in here rather than rely on core handling of IIO_VAL_FRACTIONAL.
That would give us a greater potential range.  There may still be values
we can't represent, but it should be less restrictive that this
assumption. (pity as this was neater!)

> +		if (min_range_high != 0xFFFFFFFF)
> +			return -EINVAL;
> +
> +		*val = min_range_low;
> +		*val2 = 1;
> +	}
> +	return 0;
> +}
> +
> +static int scmi_iio_set_sensor_range_avail(struct iio_dev *iio_dev)
> +{
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	int ret;
> +
> +	ret = scmi_iio_get_sensor_min_range(iio_dev, &sensor->range_avail[0],
> +					    &sensor->range_avail[1]);
> +	if (ret)
> +		return ret;
> +
> +	scmi_iio_get_sensor_resolution(iio_dev, &sensor->range_avail[2],
> +				       &sensor->range_avail[3]);
> +	ret = scmi_iio_get_sensor_max_range(iio_dev, &sensor->range_avail[4],
> +					    &sensor->range_avail[5]);
> +	return ret;
> +}
> +
> +static int scmi_iio_set_sampling_freq_avail(struct iio_dev *iio_dev)
> +{
> +	u64 cur_interval_ns, low_interval_ns, high_interval_ns, step_size_ns,
> +		hz, uhz;
> +	unsigned int cur_interval, low_interval, high_interval, step_size;
> +	struct scmi_iio_priv *sensor = iio_priv(iio_dev);
> +	int i;
> +
> +	sensor->freq_avail = devm_kzalloc(&iio_dev->dev,
> +					  sizeof(u32) * (sensor->sensor_info->intervals.count * 2),

Slight preference for sizeof(*sensor->freq_avail) *...
as saves reviewer having to go check types match up.

> +					  GFP_KERNEL);
> +	if (!sensor->freq_avail)
> +		return -ENOMEM;
> +
> +	if (sensor->sensor_info->intervals.segmented) {
> +		low_interval = sensor->sensor_info->intervals
> +				       .desc[SCMI_SENS_INTVL_SEGMENT_LOW];
> +		low_interval_ns = scmi_iio_convert_interval_to_ns(low_interval);
> +		convert_ns_to_freq(low_interval_ns, &hz, &uhz);
> +		sensor->freq_avail[0] = hz;
> +		sensor->freq_avail[1] = uhz;
> +
> +		step_size = sensor->sensor_info->intervals
> +				    .desc[SCMI_SENS_INTVL_SEGMENT_STEP];
> +		step_size_ns = scmi_iio_convert_interval_to_ns(step_size);
> +		convert_ns_to_freq(step_size_ns, &hz, &uhz);
> +		sensor->freq_avail[2] = hz;
> +		sensor->freq_avail[3] = uhz;
> +
> +		high_interval = sensor->sensor_info->intervals
> +					.desc[SCMI_SENS_INTVL_SEGMENT_HIGH];
> +		high_interval_ns =
> +			scmi_iio_convert_interval_to_ns(high_interval);
> +		convert_ns_to_freq(high_interval_ns, &hz, &uhz);
> +		sensor->freq_avail[4] = hz;
> +		sensor->freq_avail[5] = uhz;
> +	} else {
> +		for (i = 0; i < sensor->sensor_info->intervals.count; i++) {
> +			cur_interval = sensor->sensor_info->intervals.desc[i];
> +			cur_interval_ns = scmi_iio_convert_interval_to_ns(cur_interval);
> +			convert_ns_to_freq(cur_interval_ns, &hz, &uhz);
> +			sensor->freq_avail[i * 2] = hz;
> +			sensor->freq_avail[i * 2 + 1] = uhz;
> +		}
> +	}
> +	return 0;
> +}
> +
> +static int scmi_iio_buffers_setup(struct iio_dev *scmi_iiodev)
> +{
> +	struct iio_buffer *buffer;
> +
> +	buffer = devm_iio_kfifo_allocate(&scmi_iiodev->dev);
> +	if (!buffer)
> +		return -ENOMEM;
> +
> +	iio_device_attach_buffer(scmi_iiodev, buffer);
> +	scmi_iiodev->modes |= INDIO_BUFFER_SOFTWARE;
> +	scmi_iiodev->setup_ops = &scmi_iio_buffer_ops;
> +	return 0;
> +}
> +
> +static int scmi_alloc_iiodev(struct device *dev, struct scmi_handle *handle,
> +			     const struct scmi_sensor_info *sensor_info,
> +			     struct iio_dev **scmi_iio_dev)

Perhaps it would be nice to use PTR_ERR etc and have this function just return
the struct iio_dev.   That would fit with more common form for allocation functions.

> +{
> +	struct iio_chan_spec *iio_channels;
> +	struct scmi_iio_priv *sensor;
> +	enum iio_modifier modifier;
> +	enum iio_chan_type type;
> +	struct iio_dev *iiodev;
> +	int i, ret;
> +
> +	iiodev = devm_iio_device_alloc(dev, sizeof(*sensor));
> +	if (!iiodev)
> +		return -ENOMEM;
> +
> +	iiodev->modes = INDIO_DIRECT_MODE;
> +	iiodev->dev.parent = dev;
> +	sensor = iio_priv(iiodev);
> +	sensor->handle = handle;
> +	sensor->sensor_info = sensor_info;
> +	sensor->sensor_update_nb.notifier_call = scmi_iio_sensor_update_cb;
> +	sensor->indio_dev = iiodev;
> +
> +	/* adding one additional channel for timestamp */
> +	iiodev->num_channels = sensor_info->num_axis + 1;
> +	iiodev->name = sensor_info->name;
> +	iiodev->info = &scmi_iio_info;
> +
> +	iio_channels =
> +		devm_kzalloc(dev,
> +			     sizeof(*iio_channels) * (iiodev->num_channels),
> +			     GFP_KERNEL);
> +	if (!iio_channels)
> +		return -ENOMEM;
> +
> +	scmi_iio_set_sampling_freq_avail(iiodev);
> +
> +	ret = scmi_iio_set_sensor_range_avail(iiodev);
> +	if (ret) {
> +		dev_err(dev, "Error while setting the sensor %s range %d",
> +			sensor_info->name, ret);
> +		return ret;
> +	}
> +
> +	for (i = 0; i < sensor_info->num_axis; i++) {
> +		ret = scmi_iio_get_chan_type(sensor_info->axis[i].type, &type);
> +		if (ret < 0)
> +			return ret;
> +
> +		ret = scmi_iio_get_chan_modifier(sensor_info->axis[i].name,
> +						 &modifier);
> +		if (ret < 0)
> +			return ret;
> +
> +		scmi_iio_set_data_channel(&iio_channels[i], type, modifier,
> +					  sensor_info->axis[i].id);
> +	}
> +
> +	scmi_iio_set_timestamp_channel(&iio_channels[i], i);
> +	iiodev->channels = iio_channels;
> +	*scmi_iio_dev = iiodev;
> +	return ret;
> +}
> +
> +static int scmi_iio_dev_probe(struct scmi_device *sdev)
> +{
> +	const struct scmi_sensor_info *sensor_info;
> +	struct scmi_handle *handle = sdev->handle;
> +	struct device *dev = &sdev->dev;
> +	struct iio_dev *scmi_iio_dev;
> +	u16 nr_sensors;
> +	int err, i;
> +
> +	if (!handle || !handle->sensor_ops) {
> +		dev_err(dev, "SCMI device has no sensor interface\n");
I'm going to guess we can't actually get here because the registration
would't have happened if either of those are true?
If so perhaps drop the error message.

> +		return -EINVAL;
> +	}
> +
> +	nr_sensors = handle->sensor_ops->count_get(handle);
> +	if (!nr_sensors) {
> +		dev_dbg(dev, "0 sensors found via SCMI bus\n");
-ENODEV maybe?
> +		return -EINVAL;
> +	}
> +
> +	dev_dbg(dev, "%d sensors found via SCMI bus\n", nr_sensors);

Clear out any debug prints out that don't provide info that can't be obtained
farily easily from elsewhere.  In this case they will either be registered
or not and we'll get error messages.
These sort of prints bitrot over time so we want to limit them to the truely
useful.

> +
> +	for (i = 0; i < nr_sensors; i++) {
> +		sensor_info = handle->sensor_ops->info_get(handle, i);
> +		if (!sensor_info) {
> +			dev_err(dev, "SCMI sensor %d has missing info\n", i);
> +			return -EINVAL;
> +		}
> +
> +		/* Skipping scalar sensor,as this driver only supports accel and gyro */
> +		if (sensor_info->num_axis == 0)
> +			continue;

So there is a situation where this driver never creates anything?  In that path I'd
like to see an -ENODEV error return.

> +
> +		err = scmi_alloc_iiodev(dev, handle, sensor_info,
> +					&scmi_iio_dev);
> +		if (err < 0) {
> +			dev_err(dev,
> +				"failed to allocate IIO device for sensor %s: %d\n",
> +				sensor_info->name, err);
> +			return err;
> +		}
> +
> +		err = scmi_iio_buffers_setup(scmi_iio_dev);
> +		if (err < 0) {
> +			dev_err(dev,
> +				"IIO buffer setup error at sensor %s: %d\n",
> +				sensor_info->name, err);
> +			return err;
> +		}
> +
> +		err = devm_iio_device_register(dev, scmi_iio_dev);
> +		if (err) {
> +			dev_err(dev,
> +				"IIO device registration failed at sensor %s: %d\n",
> +				sensor_info->name, err);
> +			return err;
> +		}
> +	}
> +	return err;
> +}
> +
> +static const struct scmi_device_id scmi_id_table[] = {
> +	{ SCMI_PROTOCOL_SENSOR, "iiodev" },

I'm curious on this.  What actually causes a match on that
iiodev?  From digging around the scmi core am I right in thinking
that this iiodev id needs to be explicitly listed?

It would be good to include any changes needed there in this
series.

> +	{},
> +};
> +
> +MODULE_DEVICE_TABLE(scmi, scmi_id_table);
> +
> +static struct scmi_driver scmi_iiodev_driver = {
> +	.name = "scmi-sensor-iiodev",
> +	.probe = scmi_iio_dev_probe,
> +	.id_table = scmi_id_table,
> +};
> +
> +module_scmi_driver(scmi_iiodev_driver);
> +
> +MODULE_AUTHOR("Jyoti Bhayana <jbhayana@google.com>");
> +MODULE_DESCRIPTION("SCMI IIO Driver");
> +MODULE_LICENSE("GPL v2");