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Date:   Sun, 22 Nov 2020 14:14:16 +0000
From:   Jonathan Cameron <jic23@kernel.org>
To:     "Pandruvada, Srinivas" <srinivas.pandruvada@intel.com>
Cc:     "Ye, Xiang" <xiang.ye@intel.com>,
        "jikos@kernel.org" <jikos@kernel.org>,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>
Subject: Re: [PATCH v2 4/4] iio: hid-sensors: Add hinge sensor driver
Message-ID: <20201122141416.7f446793@archlinux>
In-Reply-To: <1de3727a37fe1d793b6146d9c19b101e32bb1c71.camel@intel.com>
References: <20201119100331.2594-1-xiang.ye@intel.com>
        <20201119100331.2594-5-xiang.ye@intel.com>
        <20201121175629.057031af@archlinux>
        <218c8869f799d701ddd5c22ce9524a765f43a0de.camel@intel.com>
        <1de3727a37fe1d793b6146d9c19b101e32bb1c71.camel@intel.com>
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On Sun, 22 Nov 2020 02:14:16 +0000
"Pandruvada, Srinivas" <srinivas.pandruvada@intel.com> wrote:

> On Sat, 2020-11-21 at 17:46 -0800, Srinivas Pandruvada wrote:
> > On Sat, 2020-11-21 at 17:56 +0000, Jonathan Cameron wrote:  
> > > On Thu, 19 Nov 2020 18:03:31 +0800
> > > Ye Xiang <xiang.ye@intel.com> wrote:
> > >   
> > > > The Hinge sensor is a common custom sensor on laptops. It
> > > > calculates
> > > > the angle between the lid (screen) and the base (keyboard). In
> > > > addition,
> > > > it also exposes screen and the keyboard angels with respect to
> > > > the
> > > > ground. Applications can easily get laptop's status in space
> > > > through
> > > > this sensor, in order to display appropriate user interface.  
> > > 
> > > I'm a little unclear on why the 3 axes aren't treated as a single
> > > sensor.
> > > You seem to always grab the 3 together or am I missing something?
> > > 
> > > That will greatly simplify things and get rid of the need to have
> > > a shared trigger with the problems that causes in the previous
> > > patch.  
> > 
> > They are not three axes, they are independent. Xiang did try adding
> > x,
> > y and z component to represent x as hinge, y as keyboard and z as
> > lid.
> > But I was not convinced.
> > The problem is that then what will be sysfs interface? They are
> > really
> > a three sensors. Or we create new interface to call
> > in_angl_raw_keyboard
> > in_angl_raw_screen
> > in_angl_raw_lid.
> >   
> You seem to indicate this is possible now some new "label" patch.
> Is this the patch?
> commit 2c3d0c9ffd24d9b4c62c5dfb2104695a614be28c
> Author: Phil Reid <preid@electromag.com.au>
> Date:   Thu Sep 19 22:36:08 2019 +0800

Nope, this one 
https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?id=1d4ef9b39ebecca827642b8897d2d79ea2026682

The one above adds a per device label which wouldn't be much use for your
case, but this one adds a per channel label.

Done via a read_label callback.

Here you'd want to use indexed channels so something like.

in_angl0_raw
in_angl1_raw
in_angl2_raw

and

in_angl0_label = keyboard
in_angl1_label = screen
in_angl2_label = lid


> 
> Ideally, one iio device here is much easy to manage as other HID
> sensors. If we can add something other that "x", "y" and "z" component.

Agreed, using axes makes no real sense here and extended_name is
just a mess from ABI point of view.  Trying to solve this was the
reason we added the _label interface.

Jonathan


> 
> Thanks,
> Srinivas
> 
> > Thanks,
> > Srinivas
> > 
> >   
> > > Thanks,
> > > 
> > > Jonathan
> > >   
> > > > Signed-off-by: Ye Xiang <xiang.ye@intel.com>
> > > > ---
> > > >  .../hid-sensors/hid-sensor-attributes.c       |   2 +
> > > >  drivers/iio/position/Kconfig                  |  16 +
> > > >  drivers/iio/position/Makefile                 |   3 +
> > > >  .../iio/position/hid-sensor-custom-hinge.c    | 412
> > > > ++++++++++++++++++  
> > > 
> > > Given it's custom probably needs a more specific name.  I guess
> > > hid-sensor-custom-intel-hinge.c might be safe?
> > > 
> > > Same for other places we need names in here.
> > >   
> > > >  4 files changed, 433 insertions(+)
> > > >  create mode 100644 drivers/iio/position/hid-sensor-custom-
> > > > hinge.c
> > > > 
> > > > diff --git a/drivers/iio/common/hid-sensors/hid-sensor-
> > > > attributes.c 
> > > > b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> > > > index 442ff787f7af..5b822a4298a0 100644
> > > > --- a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> > > > +++ b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> > > > @@ -71,6 +71,8 @@ static struct {
> > > >  	{HID_USAGE_SENSOR_TEMPERATURE, HID_USAGE_SENSOR_UNITS_DEGREES,
> > > > 1000, 0},
> > > >  
> > > >  	{HID_USAGE_SENSOR_HUMIDITY, 0, 1000, 0},
> > > > +	{HID_USAGE_SENSOR_HINGE, 0, 0, 17453293},
> > > > +	{HID_USAGE_SENSOR_HINGE, HID_USAGE_SENSOR_UNITS_DEGREES, 0,
> > > > 17453293},
> > > >  };
> > > >  
> > > >  static void simple_div(int dividend, int divisor, int *whole,
> > > > diff --git a/drivers/iio/position/Kconfig
> > > > b/drivers/iio/position/Kconfig
> > > > index eda67f008c5b..0346f6f2b422 100644
> > > > --- a/drivers/iio/position/Kconfig
> > > > +++ b/drivers/iio/position/Kconfig
> > > > @@ -16,4 +16,20 @@ config IQS624_POS
> > > >  	  To compile this driver as a module, choose M here: the module
> > > >  	  will be called iqs624-pos.
> > > >  
> > > > +config HID_SENSOR_CUSTOM_HINGE
> > > > +	depends on HID_SENSOR_HUB
> > > > +	select IIO_BUFFER
> > > > +	select IIO_TRIGGERED_BUFFER
> > > > +	select HID_SENSOR_IIO_COMMON
> > > > +	select HID_SENSOR_IIO_TRIGGER
> > > > +	tristate "HID Hinge"
> > > > +	help
> > > > +	  This sensor present three angles, hinge angel, screen angles
> > > > +	  and keyboard angle respect to horizon (ground).
> > > > +	  Say yes here to build support for the HID SENSOR CUSTOM
> > > > +	  HINGE.  
> > > 
> > > Capitalization is a bit odd looking. I'd drop it.
> > >   
> > > > +
> > > > +	  To compile this driver as a module, choose M here: the
> > > > +	  module will be called hid-sensor-custom-hinge.
> > > > +
> > > >  endmenu
> > > > diff --git a/drivers/iio/position/Makefile
> > > > b/drivers/iio/position/Makefile
> > > > index 3cbe7a734352..7a6225977a01 100644
> > > > --- a/drivers/iio/position/Makefile
> > > > +++ b/drivers/iio/position/Makefile
> > > > @@ -5,3 +5,6 @@
> > > >  # When adding new entries keep the list in alphabetical order
> > > >  
> > > >  obj-$(CONFIG_IQS624_POS)	+= iqs624-pos.o
> > > > +
> > > > +obj-$(CONFIG_HID_SENSOR_CUSTOM_HINGE) += hid-sensor-custom-
> > > > hinge.o  
> > > 
> > > Alphabetical order preferred.
> > >   
> > > > +ccflags-y	+= -I$(srctree)/drivers/iio/common/hid-sensors  
> > > 
> > > Why?
> > >   
> > > > diff --git a/drivers/iio/position/hid-sensor-custom-hinge.c
> > > > b/drivers/iio/position/hid-sensor-custom-hinge.c
> > > > new file mode 100644
> > > > index 000000000000..a91b333f36fa
> > > > --- /dev/null
> > > > +++ b/drivers/iio/position/hid-sensor-custom-hinge.c
> > > > @@ -0,0 +1,412 @@
> > > > +// SPDX-License-Identifier: GPL-2.0-only
> > > > +/*
> > > > + * HID Sensors Driver
> > > > + * Copyright (c) 2020, Intel Corporation.
> > > > + */
> > > > +#include <linux/hid-sensor-hub.h>
> > > > +#include <linux/iio/buffer.h>
> > > > +#include <linux/iio/iio.h>
> > > > +#include <linux/platform_device.h>
> > > > +
> > > > +#include "hid-sensor-trigger.h"
> > > > +
> > > > +/* Channel definitions */
> > > > +static const struct iio_chan_spec hinge_channels[] = {
> > > > +	{ .type = IIO_ANGL,
> > > > +	  .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> > > > +	  .info_mask_shared_by_type =
> > > > +		  BIT(IIO_CHAN_INFO_OFFSET) | BIT(IIO_CHAN_INFO_SCALE)
> > > > +		  BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> > > > BIT(IIO_CHAN_INFO_HYSTERESIS),
> > > > +	  .scan_type.realbits = 16,
> > > > +	  .scan_type.storagebits = 32,  
> > > 
> > > It a bit odd to see a single channel that is 16 bits inside a 32
> > > bit
> > > with
> > > no shift or similar.  Why not just pack it into 16 bits?
> > >   
> > > > +	  .scan_type.sign = 's',
> > > > +	  .scan_index = 0 },
> > > > +
> > > > +	IIO_CHAN_SOFT_TIMESTAMP(1)
> > > > +};
> > > > +
> > > > +struct hinge_state {
> > > > +	struct iio_dev *indio_dev;
> > > > +	struct hid_sensor_hub_attribute_info hinge;
> > > > +	/* Reserve for 1 channel + pading + timestamp */
> > > > +	u32 hinge_val[1 + 3];  
> > > 
> > > __aligned(8)
> > > 
> > > see below for requirements on this.
> > > Perhaps better to use
> > > 
> > > 	struct hinge_scan {
> > > 		u32 val;
> > > 		s64 timestamp __aligned(8); // Note this is needed for
> > > x86_32
> > > 	} scan;
> > >   
> > > > +	int scale_pre_decml;
> > > > +	int scale_post_decml;
> > > > +	int scale_precision;
> > > > +	int value_offset;
> > > > +	int64_t timestamp;
> > > > +	u32 hinge_address;
> > > > +};
> > > > +
> > > > +#define IIO_DEV_NUM 3  
> > > 
> > > That needs a prefix to make it clear it's not a generic constant
> > > but is specific to this driver.
> > >   
> > > > +
> > > > +struct hinge_group {
> > > > +	struct hinge_state *hg_states[IIO_DEV_NUM];
> > > > +	struct hid_sensor_hub_callbacks callbacks;
> > > > +	struct hid_sensor_common common_attributes;
> > > > +};
> > > > +
> > > > +static struct hinge_group *hg_group;  
> > > 
> > > We shouldn't see globals like this. Please figure out how to avoid
> > > it.
> > >   
> > > > +
> > > > +/* Channel read_raw handler */
> > > > +static int hinge_read_raw(struct iio_dev *indio_dev,
> > > > +			  struct iio_chan_spec const *chan, int *val,
> > > > int *val2,
> > > > +			  long mask)
> > > > +{
> > > > +	struct hinge_state *hg_state = iio_priv(indio_dev);
> > > > +	struct hid_sensor_hub_device *hsdev;
> > > > +	int report_id = -1;
> > > > +	int ret_type;
> > > > +	s32 min;
> > > > +
> > > > +	hsdev = hg_group->common_attributes.hsdev;
> > > > +
> > > > +	*val = 0;
> > > > +	*val2 = 0;
> > > > +	switch (mask) {
> > > > +	case IIO_CHAN_INFO_RAW:
> > > > +		hid_sensor_power_state(&hg_group->common_attributes,
> > > > true);
> > > > +		report_id = hg_state->hinge.report_id;
> > > > +		min = hg_state->hinge.logical_minimum;
> > > > +		if (report_id < 0) {
> > > > +			*val = 0;
> > > > +			hid_sensor_power_state(&hg_group-  
> > > > > common_attributes,  
> > > > +					       false);
> > > > +			return -EINVAL;
> > > > +		}
> > > > +
> > > > +		*val = sensor_hub_input_attr_get_raw_value(
> > > > +			hg_group->common_attributes.hsdev, hsdev-  
> > > > > usage,  
> > > > +			hg_state->hinge_address, report_id,
> > > > SENSOR_HUB_SYNC,
> > > > +			min < 0);
> > > > +
> > > > +		hid_sensor_power_state(&hg_group->common_attributes,
> > > > false);
> > > > +		ret_type = IIO_VAL_INT;
> > > > +		break;
> > > > +	case IIO_CHAN_INFO_SCALE:
> > > > +		*val = hg_state->scale_pre_decml;
> > > > +		*val2 = hg_state->scale_post_decml;
> > > > +		ret_type = hg_state->scale_precision;
> > > > +		break;
> > > > +	case IIO_CHAN_INFO_OFFSET:
> > > > +		*val = hg_state->value_offset;
> > > > +		ret_type = IIO_VAL_INT;
> > > > +		break;
> > > > +	case IIO_CHAN_INFO_SAMP_FREQ:
> > > > +		ret_type = hid_sensor_read_samp_freq_value(
> > > > +			&hg_group->common_attributes, val, val2);
> > > > +		break;
> > > > +	case IIO_CHAN_INFO_HYSTERESIS:
> > > > +		ret_type = hid_sensor_read_raw_hyst_value(
> > > > +			&hg_group->common_attributes, val, val2);
> > > > +		break;
> > > > +	default:
> > > > +		ret_type = -EINVAL;
> > > > +		break;
> > > > +	}
> > > > +
> > > > +	return ret_type;
> > > > +}
> > > > +
> > > > +/* Channel write_raw handler */
> > > > +static int hinge_write_raw(struct iio_dev *indio_dev,
> > > > +			   struct iio_chan_spec const *chan, int val,
> > > > int val2,
> > > > +			   long mask)
> > > > +{
> > > > +	int ret;
> > > > +
> > > > +	switch (mask) {
> > > > +	case IIO_CHAN_INFO_SAMP_FREQ:
> > > > +		ret = hid_sensor_write_samp_freq_value(
> > > > +			&hg_group->common_attributes, val, val2);
> > > > +		break;
> > > > +	case IIO_CHAN_INFO_HYSTERESIS:
> > > > +		ret = hid_sensor_write_raw_hyst_value(
> > > > +			&hg_group->common_attributes, val, val2);
> > > > +
> > > > +		break;
> > > > +	default:
> > > > +		ret = -EINVAL;
> > > > +	}
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +static const struct iio_info hinge_info = {
> > > > +	.read_raw = &hinge_read_raw,
> > > > +	.write_raw = &hinge_write_raw,
> > > > +};
> > > > +
> > > > +/*
> > > > + * Function to push data to buffer;
> > > > + * wrapper added for symmetry with other hid-sensor drivers
> > > > + */
> > > > +static void hid_sensor_push_data(struct iio_dev *indio_dev, void
> > > > *data, int len,  
> > > 
> > > This doesn't seem to be generic, so don't name it as such.
> > >   
> > > > +				 int64_t timestamp)
> > > > +{
> > > > +	iio_push_to_buffers_with_timestamp(indio_dev, data, timestamp);  
> > > I hope that data buffer obeys the various rules needed by (and
> > > admittedly
> > > not that well documented) iio_push_to_buffers_with_timestamp()
> > > 
> > > 1. Needs to be 8 byte aligned.
> > > 2. Needs to have space for an aligned 8 byte timestamp at the end.
> > >   
> > > > +}
> > > > +
> > > > +/*
> > > > + * Callback handler to send event after all samples are received
> > > > + * and captured.
> > > > + */
> > > > +static int hinge_proc_event(struct hid_sensor_hub_device *hsdev,
> > > > +			    unsigned int usage_id, void *priv)
> > > > +{
> > > > +	int i;
> > > > +
> > > > +	for (i = 0; i < IIO_DEV_NUM; ++i) {  
> > > If we push for all sensors together, better to have
> > > this as a single iio_device with 3 channels.
> > > 
> > > Use the channel labels (just added to IIO) to identify which is
> > > which.
> > >   
> > > > +		struct hinge_state *hg_state;
> > > > +		struct iio_dev *indio_dev;
> > > > +
> > > > +		hg_state = hg_group->hg_states[i];
> > > > +		indio_dev = hg_state->indio_dev;
> > > > +
> > > > +		dev_dbg(&indio_dev->dev, "%s timestamp:%llu
> > > > scan_bytes:%d\n",
> > > > +			__func__, hg_state->timestamp, indio_dev-  
> > > > > scan_bytes);  
> > > > +
> > > > +		if (!hg_state->timestamp)
> > > > +			hg_state->timestamp =
> > > > iio_get_time_ns(indio_dev);
> > > > +
> > > > +		hid_sensor_push_data(indio_dev, hg_state->hinge_val,
> > > > +				     sizeof(hg_state->hinge_val),
> > > > +				     hg_state->timestamp);
> > > > +
> > > > +		hg_state->timestamp = 0;
> > > > +	}
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +/* Capture samples in local storage */
> > > > +static int hinge_capture_sample(struct hid_sensor_hub_device
> > > > *hsdev,
> > > > +				unsigned int usage_id, size_t raw_len,
> > > > +				char *raw_data, void *priv)
> > > > +{
> > > > +	struct hinge_state *hg_state;
> > > > +	int offset;
> > > > +	int ret = -EINVAL;
> > > > +	int i;
> > > > +
> > > > +	if (usage_id == HID_USAGE_SENSOR_TIME_TIMESTAMP) {
> > > > +		for (i = 0; i < IIO_DEV_NUM; i++)
> > > > +			hg_group->hg_states[i]->timestamp =  
> > > 
> > > This rather implies all the data is captured together... If so
> > > single
> > > iio_device may make more sense.
> > >   
> > > > +				hid_sensor_convert_timestamp(
> > > > +					&hg_group->common_attributes,
> > > > +					*(int64_t *)raw_data);
> > > > +		return 0;
> > > > +	}
> > > > +
> > > > +	switch (usage_id) {
> > > > +	case HID_USAGE_SENSOR_DATA_FIELD_CUSTOM_VALUE_1:
> > > > +	case HID_USAGE_SENSOR_DATA_FIELD_CUSTOM_VALUE_2:
> > > > +	case HID_USAGE_SENSOR_DATA_FIELD_CUSTOM_VALUE_3:
> > > > +		offset = usage_id -
> > > > HID_USAGE_SENSOR_DATA_FIELD_CUSTOM_VALUE_1;
> > > > +		hg_state = hg_group->hg_states[offset];
> > > > +		hg_state->hinge_val[0] = *(u32 *)raw_data;
> > > > +		ret = 0;  
> > > 
> > > 		return 0;
> > >   
> > > > +		break;
> > > > +	default:  
> > > 		return -EINVAL;  
> > > > +		break;
> > > > +	}
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +/* Parse report which is specific to an usage id */
> > > > +static int hinge_parse_report(struct platform_device *pdev,
> > > > +			      struct hid_sensor_hub_device *hsdev,
> > > > +			      unsigned int usage_id, unsigned int
> > > > attr_usage_id,
> > > > +			      struct hinge_state *st)
> > > > +{
> > > > +	int ret;
> > > > +
> > > > +	ret = sensor_hub_input_get_attribute_info(
> > > > +		hsdev, HID_INPUT_REPORT, usage_id, attr_usage_id, &st-  
> > > > > hinge);  
> > > > +	if (ret < 0)
> > > > +		return ret;
> > > > +
> > > > +	st->hinge_address = attr_usage_id;
> > > > +	st->scale_precision =
> > > > +		hid_sensor_format_scale(HID_USAGE_SENSOR_HINGE, &st-  
> > > > > hinge,  
> > > > +					&st->scale_pre_decml,
> > > > +					&st->scale_post_decml);
> > > > +
> > > > +	/* Set Sensitivity field ids, when there is no individual
> > > > modifier */
> > > > +	if (hg_group->common_attributes.sensitivity.index < 0) {
> > > > +		sensor_hub_input_get_attribute_info(
> > > > +			hsdev, HID_FEATURE_REPORT, usage_id,
> > > > +			HID_USAGE_SENSOR_DATA_MOD_CHANGE_SENSITIVITY_AB
> > > > S |
> > > > +				HID_USAGE_SENSOR_DATA_FIELD_CUSTOM_VALU
> > > > E_1,
> > > > +			&hg_group->common_attributes.sensitivity);
> > > > +		dev_dbg(&pdev->dev, "Sensitivity index:report %d:%d\n",
> > > > +			hg_group->common_attributes.sensitivity.index,
> > > > +			hg_group-  
> > > > > common_attributes.sensitivity.report_id);  
> > > > +	}
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +/* Function to initialize the processing for usage id */
> > > > +static int hinge_add_iio_device(struct platform_device *pdev,
> > > > int
> > > > index,
> > > > +				const char *name, struct hinge_state
> > > > **st)
> > > > +{
> > > > +	struct hid_sensor_hub_device *hsdev = pdev->dev.platform_data;
> > > > +	struct hinge_state *hg_state;
> > > > +	struct iio_dev *indio_dev;
> > > > +	int ret;
> > > > +
> > > > +	indio_dev =
> > > > +		devm_iio_device_alloc(&pdev->dev, sizeof(struct
> > > > hinge_state));  
> > > 
> > > sizeof (*hg_state) preferred.
> > >   
> > > > +	if (indio_dev == NULL)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	hg_state = iio_priv(indio_dev);
> > > > +	hg_state->indio_dev = indio_dev;
> > > > +
> > > > +	indio_dev->num_channels = ARRAY_SIZE(hinge_channels);
> > > > +	indio_dev->channels =
> > > > +		kmemdup(hinge_channels, sizeof(hinge_channels),
> > > > GFP_KERNEL);  
> > > 
> > > I don't immediately see anything that is modifying channels. As
> > > such
> > > you
> > > should be able have it shared by all the instances.
> > >   
> > > > +	if (!indio_dev->channels)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	ret = hinge_parse_report(
> > > > +		pdev, hsdev, hsdev->usage,
> > > > +		HID_USAGE_SENSOR_DATA_FIELD_CUSTOM_VALUE_1 + index,
> > > > hg_state);
> > > > +	if (ret) {
> > > > +		dev_err(&pdev->dev, "failed to setup attributes\n");
> > > > +		goto error_free_dev_mem;
> > > > +	}
> > > > +
> > > > +	indio_dev->dev.parent = &pdev->dev;
> > > > +	indio_dev->info = &hinge_info;
> > > > +	indio_dev->name = name;
> > > > +	indio_dev->modes = INDIO_DIRECT_MODE;
> > > > +
> > > > +	ret = hid_sensor_setup_trigger(indio_dev, name,
> > > > +				       &hg_group->common_attributes);
> > > > +	if (ret < 0) {
> > > > +		dev_err(&pdev->dev, "trigger setup failed\n");
> > > > +		goto error_free_dev_mem;
> > > > +	}
> > > > +
> > > > +	ret = iio_device_register(indio_dev);
> > > > +	if (ret) {
> > > > +		dev_err(&pdev->dev, "device register failed\n");
> > > > +		goto error_remove_trigger;
> > > > +	}
> > > > +
> > > > +	*st = hg_state;
> > > > +
> > > > +	return ret;
> > > > +
> > > > +error_remove_trigger:
> > > > +	hid_sensor_remove_trigger(indio_dev, &hg_group-  
> > > > > common_attributes);  
> > > > +error_free_dev_mem:
> > > > +	kfree(indio_dev->channels);
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +/* Function to deinitialize the processing for usage id */
> > > > +static int hinge_remove_iio_device(struct platform_device *pdev,
> > > > int index)
> > > > +{
> > > > +	struct hinge_state *hg_state = hg_group->hg_states[index];
> > > > +	struct iio_dev *indio_dev = hg_state->indio_dev;
> > > > +
> > > > +	iio_device_unregister(indio_dev);
> > > > +	hid_sensor_remove_trigger(indio_dev, &hg_group-  
> > > > > common_attributes);  
> > > > +	kfree(indio_dev->channels);
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static int hid_hinge_probe(struct platform_device *pdev)
> > > > +{
> > > > +	struct hinge_state *hg_state;
> > > > +	struct hid_sensor_hub_device *hsdev = pdev->dev.platform_data;
> > > > +	static const char *const names[] = { "hinge", "screen",
> > > > "keyboard" };
> > > > +	int ret;
> > > > +	int i;
> > > > +
> > > > +	hg_group = devm_kzalloc(&pdev->dev, sizeof(struct hinge_group),
> > > > +				GFP_KERNEL);  
> > > 
> > > As mentioned above, I'd really not expect to see a global like
> > > this.
> > > Technically nothing stops there being more than one instance of
> > > this
> > > device on a platform (even if that would be a bit odd) + it's
> > > almost
> > > always cleaner to not use a global in the first place.
> > >   
> > > > +	if (!hg_group)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	hg_group->common_attributes.hsdev = hsdev;
> > > > +	hg_group->common_attributes.pdev = pdev;
> > > > +
> > > > +	ret = hid_sensor_parse_common_attributes(hsdev, hsdev->usage,
> > > > +						 &hg_group-  
> > > > > common_attributes);  
> > > > +	if (ret) {
> > > > +		dev_err(&pdev->dev, "failed to setup common
> > > > attributes\n");
> > > > +		return ret;
> > > > +	}
> > > > +
> > > > +	atomic_set(&hg_group->common_attributes.data_ready, 0);
> > > > +	for (i = 0; i < IIO_DEV_NUM; i++) {
> > > > +		ret = hinge_add_iio_device(pdev, i, names[i],
> > > > &hg_state);
> > > > +		if (ret)
> > > > +			goto err_probe;
> > > > +
> > > > +		hg_group->hg_states[i] = hg_state;
> > > > +	}
> > > > +
> > > > +	/* use the first iio device to do the PM */
> > > > +	platform_set_drvdata(pdev, hg_group->hg_states[0]->indio_dev);
> > > > +
> > > > +	hg_group->callbacks.send_event = hinge_proc_event;
> > > > +	hg_group->callbacks.capture_sample = hinge_capture_sample;
> > > > +	hg_group->callbacks.pdev = pdev;
> > > > +	ret = sensor_hub_register_callback(hsdev, hsdev->usage,
> > > > +					   &hg_group->callbacks);
> > > > +	if (ret < 0)
> > > > +		dev_err(&pdev->dev, "callback reg failed\n");
> > > > +
> > > > +	return ret;
> > > > +
> > > > +err_probe:
> > > > +	for (i--; i >= 0; i--)
> > > > +		hinge_remove_iio_device(pdev, i);
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +/* Function to deinitialize the processing for usage id */
> > > > +static int hid_hinge_remove(struct platform_device *pdev)
> > > > +{
> > > > +	struct hid_sensor_hub_device *hsdev = pdev->dev.platform_data;
> > > > +	int i;
> > > > +
> > > > +	sensor_hub_remove_callback(hsdev, hsdev->usage);
> > > > +
> > > > +	for (i = 0; i < IIO_DEV_NUM; i++)
> > > > +		hinge_remove_iio_device(pdev, i);
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +static const struct platform_device_id hid_hinge_ids[] = {
> > > > +	{
> > > > +		/* Format: HID-SENSOR-INT-usage_id_in_hex_lowercase */
> > > > +		.name = "HID-SENSOR-INT-020b",
> > > > +	},
> > > > +	{ /* sentinel */ }
> > > > +};
> > > > +MODULE_DEVICE_TABLE(platform, hid_hinge_ids);
> > > > +
> > > > +static struct platform_driver hid_hinge_platform_driver = {
> > > > +	.id_table = hid_hinge_ids,
> > > > +	.driver = {
> > > > +		.name	= KBUILD_MODNAME,
> > > > +		.pm	= &hid_sensor_pm_ops,
> > > > +	},
> > > > +	.probe		= hid_hinge_probe,
> > > > +	.remove		= hid_hinge_remove,
> > > > +};
> > > > +module_platform_driver(hid_hinge_platform_driver);
> > > > +
> > > > +MODULE_DESCRIPTION("HID Sensor Custom Hinge");
> > > > +MODULE_AUTHOR("Ye Xiang <xiang.ye@intel.com>");
> > > > +MODULE_LICENSE("GPL");