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Date:   Sun, 12 Apr 2020 12:06:48 +0100
From:   Jonathan Cameron <jic23@...23.retrosnub.co.uk>
To:     Gwendal Grignou <gwendal@...omium.org>
Cc:     bleung@...omium.org, vilhelm.gray@...il.com,
        enric.balletbo@...labora.com, ic23@...nel.org, groeck@...omium.org,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH] drivers: counter: Add Cros EC Sync counter

On Tue,  7 Apr 2020 22:36:55 -0700
Gwendal Grignou <gwendal@...omium.org> wrote:

> When the camera vsync pin is connected to the embedded controller (EC) of
> a chromebook, the EC reports a sensor with a counter that increases
> at each GPIO rising edge.
> 
> The sensor is presented using the counter subsystem.
> In addition, it is also presented via the IIO subsystem with a timestamp,
> allowing synchronisation with sensors connected to the same EC, for
> image stabilisation or augmented reality applications.
> 
> To enable the counter:
> via counter ABI:
> echo "rising edge" > counterX/count0/signal_action
> via iio ABI
> echo 1 > iio:deviceY/en
> 
> To disable the counter:
> via counter ABI:
> echo "none" > counterX/count0/signal_action
> via iio ABI
> echo 0 > iio:deviceY/en
> 
> To read the current counter value:
> via counter ABI:
> cat counterX/count0/count
> via iio ABI
> cat iio:deviceY/in_count_raw
> We can also read the value through the IIO buffer:
> echo 1 > iio:deviceY/scan_elements/in_timestamp_en
> echo 1 > iio:deviceY/scan_elements/in_count_en
> echo 1 > iio:deviceY/buffer/enable
> 
> and each time to counter increase, the following binary blob
> will be appended to dev/iio:deviceY:
> 000f 0000 0000 0000 dc66 816c 0071 0000
>  \   <-- padding -> <-- timestamp ---->
>   count
> 
> Signed-off-by: Gwendal Grignou <gwendal@...omium.org>
> ---
> An initial version of the driver was presented few month ago at
> https://patchwork.kernel.org/patch/11037009/
> 
>  drivers/counter/Kconfig                       |  11 +
>  drivers/counter/Makefile                      |   1 +
>  drivers/counter/cros_ec_sync.c                | 342 ++++++++++++++++++
>  .../cros_ec_sensors/cros_ec_sensors_core.c    |  15 +
>  drivers/platform/chrome/cros_ec_sensorhub.c   |   3 +
>  .../linux/iio/common/cros_ec_sensors_core.h   |   4 +-
>  6 files changed, 375 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/counter/cros_ec_sync.c
> 
> diff --git a/drivers/counter/Kconfig b/drivers/counter/Kconfig
> index c80fa76bb5311..18fde918ff40b 100644
> --- a/drivers/counter/Kconfig
> +++ b/drivers/counter/Kconfig
> @@ -29,6 +29,17 @@ config 104_QUAD_8
>  	  The base port addresses for the devices may be configured via the base
>  	  array module parameter.
>  
> +config CROS_EC_SYNC
> +	tristate "ChromeOS EC Counter driver"
> +	depends on IIO_CROS_EC_SENSORS_CORE
> +	help
> +	  Module to handle synchronisation sensor presented by the ChromeOS EC
> +	  Sensor hub.
> +	  Synchronisation sensor sends event to the host when the camera
> +	  take a picture. It allows synchronisation with other MEMS sensor,
> +	  like gyroscope for image statbilization or augmented reality
> +	  application (AR).
> +
>  config STM32_TIMER_CNT
>  	tristate "STM32 Timer encoder counter driver"
>  	depends on MFD_STM32_TIMERS || COMPILE_TEST
> diff --git a/drivers/counter/Makefile b/drivers/counter/Makefile
> index 55142d1f4c436..98378fca50ad6 100644
> --- a/drivers/counter/Makefile
> +++ b/drivers/counter/Makefile
> @@ -6,6 +6,7 @@
>  obj-$(CONFIG_COUNTER) += counter.o
>  
>  obj-$(CONFIG_104_QUAD_8)	+= 104-quad-8.o
> +obj-$(CONFIG_CROS_EC_SYNC)	+= cros_ec_sync.o
>  obj-$(CONFIG_STM32_TIMER_CNT)	+= stm32-timer-cnt.o
>  obj-$(CONFIG_STM32_LPTIMER_CNT)	+= stm32-lptimer-cnt.o
>  obj-$(CONFIG_TI_EQEP)		+= ti-eqep.o
> diff --git a/drivers/counter/cros_ec_sync.c b/drivers/counter/cros_ec_sync.c
> new file mode 100644
> index 0000000000000..94b3ababab4bd
> --- /dev/null
> +++ b/drivers/counter/cros_ec_sync.c
> @@ -0,0 +1,342 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Driver for synchronisation sensor behind CrOS EC.
> + *
> + * Copyright 2020 Google, Inc
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * This driver uses the cros-ec interface to communicate with the Chrome OS
> + * EC about counter sensors. Counters are presented through
> + * iio sysfs.
> + */
> +
> +#include <linux/counter.h>
> +#include <linux/device.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/common/cros_ec_sensors_core.h>
> +#include <linux/iio/iio.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_data/cros_ec_commands.h>
> +#include <linux/platform_data/cros_ec_proto.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +/*
> + * One channel for counter, the other for timestamp.
> + */
> +#define MAX_CHANNELS (1 + 1)
> +
> +/**
> + * struct cros_ec_sync_state - device structure
> + *
> + * @core: common structure for all cros_ec sensor.
> + *        Must be at the beggining.
> + * @channels: presented iio channels(2).
> + * @counter: counter data structure.
> + */
> +struct cros_ec_sync_state {
> +	struct cros_ec_sensors_core_state core;
> +	struct iio_chan_spec channels[MAX_CHANNELS];
> +	struct counter_device counter;
> +};
> +
> +/**
> + * cros_ec_sync_get_enable() - Check if the counter is enabled.
> + *
> + * @st:     core cros_ec sensor
> + * @val:    status: 0: disabled, 1 enabled.
> + *
> + * Return: 0 on success, -errno on failure.
> + */
> +static int cros_ec_sync_get_enable(struct cros_ec_sensors_core_state *st,
> +				   int *val)
> +{
> +	int ret;
> +
> +	mutex_lock(&st->cmd_lock);
> +	st->param.cmd = MOTIONSENSE_CMD_SENSOR_ODR;
> +	st->param.sensor_odr.data = EC_MOTION_SENSE_NO_VALUE;
> +
> +	ret = cros_ec_motion_send_host_cmd(st, 0);
> +	mutex_unlock(&st->cmd_lock);
> +	if (ret)
> +		return ret;
> +
> +	*val = !!st->resp->sensor_odr.ret;
> +	return 0;
> +}
> +
> +/**
> + * cros_ec_sync_set_enable() - Allow the counter to count.
> + *
> + * When enable, the counter will increase for each VSYNC rising edge
> + * and will produce an event in the iio buffer, if enabled.
> + *
> + * @st:     core cros_ec sensor
> + * @val:    0: disable, 1 enable.
> + *
> + * Return: 0 on success, -errno on failure.
> + */
> +static int cros_ec_sync_set_enable(struct cros_ec_sensors_core_state *st,
> +				   int val)
> +{
> +	int ret;
> +
> +	mutex_lock(&st->cmd_lock);
> +	st->param.cmd = MOTIONSENSE_CMD_SENSOR_ODR;
> +	st->param.sensor_odr.data = val;
> +	st->param.sensor_odr.roundup = 1;
> +
> +	ret = cros_ec_motion_send_host_cmd(st, 0);
> +	mutex_unlock(&st->cmd_lock);
> +	return ret;
> +}
> +
> +static int cros_ec_sync_iio_read(struct iio_dev *indio_dev,
> +				 struct iio_chan_spec const *chan,
> +				 int *val, int *val2, long mask)
> +{
> +	struct cros_ec_sensors_core_state *st = iio_priv(indio_dev);
> +	u16 data;
> +	int ret;
> +	int idx = chan->scan_index;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		mutex_lock(&st->cmd_lock);
> +		ret = cros_ec_sensors_read_cmd(indio_dev, 1 << idx, &data);
> +		mutex_unlock(&st->cmd_lock);
> +		if (ret < 0)
> +			break;
> +		ret = IIO_VAL_INT;
> +		*val = data;
> +		break;
> +	case IIO_CHAN_INFO_ENABLE:
> +		ret = cros_ec_sync_get_enable(st, val);
> +		if (ret < 0)
> +			break;
> +		ret = IIO_VAL_INT;
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +	mutex_unlock(&st->cmd_lock);
> +	return ret;
> +}
> +
> +static int cros_ec_sync_iio_write(struct iio_dev *indio_dev,
> +				  struct iio_chan_spec const *chan,
> +				  int val, int val2, long mask)
> +{
> +	struct cros_ec_sensors_core_state *st = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_ENABLE:
> +		if (val < 0 || val > 1)
> +			return -EINVAL;
> +
> +		return cros_ec_sync_set_enable(st, val);
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info cros_ec_sync_info = {
> +	.read_raw = &cros_ec_sync_iio_read,
> +	.write_raw = &cros_ec_sync_iio_write,
> +};
> +
> +/* The counter can only increase, so only one function present. */
> +static enum counter_count_function cros_ec_sync_functions[] = {
> +	COUNTER_COUNT_FUNCTION_INCREASE,
> +};
> +
> +/* 2 synapse actions allowed: count for each rising edge, or not. */
> +static enum counter_synapse_action cros_ec_sync_synapse_actions[] = {
> +	COUNTER_SYNAPSE_ACTION_NONE,
> +	COUNTER_SYNAPSE_ACTION_RISING_EDGE,
> +};
> +
> +static int cros_ec_sync_read_count(struct counter_device *counter,
> +				   struct counter_count *count,
> +				   unsigned long *val)
> +{
> +	struct cros_ec_sensors_core_state *st = counter->priv;
> +	u16 raw;
> +	int ret;
> +
> +	mutex_lock(&st->cmd_lock);
> +	ret = cros_ec_sensors_read_cmd(iio_priv_to_dev(st), 1, &raw);
> +	mutex_unlock(&st->cmd_lock);
> +	if (ret)
> +		return ret;
> +
> +	*val = raw;
> +	return 0;
> +}
> +
> +static int cros_ec_sync_function_get(struct counter_device *counter,
> +				     struct counter_count *count,
> +				     size_t *function)
> +{
> +	*function = 0;
> +	return 0;
> +}
> +
> +static int cros_ec_sync_action_get(struct counter_device *counter,
> +				   struct counter_count *count,
> +				   struct counter_synapse *synapse,
> +				   size_t *action)
> +{
> +	struct cros_ec_sensors_core_state *st = counter->priv;
> +	int ret;
> +	int raw;
> +
> +	ret = cros_ec_sync_get_enable(st, &raw);
> +	if (ret)
> +		return ret;
> +
> +	*action = !!raw;
> +	return 0;
> +}
> +
> +static int cros_ec_sync_action_set(struct counter_device *counter,
> +				   struct counter_count *count,
> +				   struct counter_synapse *synapse,
> +				   size_t action)
> +{
> +	struct cros_ec_sensors_core_state *st = counter->priv;
> +
> +	return cros_ec_sync_set_enable(st, action);
> +}
> +
> +static const struct counter_ops cros_ec_sync_ops = {
> +	.count_read = cros_ec_sync_read_count,
> +	.function_get = cros_ec_sync_function_get,
> +	.action_get = cros_ec_sync_action_get,
> +	.action_set = cros_ec_sync_action_set,
> +};
> +
> +static struct counter_signal cros_ec_sync_signals[] = {
> +	{
> +		.id = 0,
> +		.name = "vsync"
> +	}
> +};
> +
> +static struct counter_synapse cros_ec_sync_synapses[] = {
> +	{
> +		.actions_list = cros_ec_sync_synapse_actions,
> +		.num_actions = ARRAY_SIZE(cros_ec_sync_synapse_actions),
> +		.signal = cros_ec_sync_signals
> +	}
> +};
> +
> +static struct counter_count cros_ec_sync_counts[] = {
> +	{
> +		.id = 0,
> +		.name = "vsync",
> +		.functions_list = cros_ec_sync_functions,
> +		.num_functions = ARRAY_SIZE(cros_ec_sync_functions),
> +		.synapses = cros_ec_sync_synapses,
> +		.num_synapses = ARRAY_SIZE(cros_ec_sync_synapses),
> +	}
> +};
> +
> +static int cros_ec_sync_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct iio_dev *indio_dev;
> +	struct cros_ec_sync_state *state;
> +	struct iio_chan_spec *channel;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*state));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	ret = cros_ec_sensors_core_init(pdev, indio_dev, true,
> +					cros_ec_sensors_capture,
> +					cros_ec_sensors_push_data);
> +	if (ret)
> +		return ret;
> +
> +	indio_dev->info = &cros_ec_sync_info;
> +	state = iio_priv(indio_dev);
> +
> +	/* Initialize IIO device */
> +	channel = state->channels;
> +
> +	/* Counter channel */
> +	channel->type = IIO_COUNT;
> +	channel->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
> +	channel->info_mask_shared_by_all = BIT(IIO_CHAN_INFO_ENABLE);
> +	channel->scan_type.realbits = CROS_EC_SENSOR_BITS;
> +	channel->scan_type.storagebits = CROS_EC_SENSOR_BITS;
> +	channel->scan_type.shift = 0;
> +	channel->scan_index = 0;
> +	channel->ext_info = cros_ec_sensors_limited_info;
> +	channel->scan_type.sign = 'u';
> +
> +	/* Timestamp channel */
> +	channel++;
> +	channel->type = IIO_TIMESTAMP;
> +	channel->channel = -1;
> +	channel->scan_index = 1;
> +	channel->scan_type.sign = 's';
> +	channel->scan_type.realbits = 64;
> +	channel->scan_type.storagebits = 64;
> +
> +	indio_dev->channels = state->channels;
> +	indio_dev->num_channels = MAX_CHANNELS;
> +
> +	state->core.read_ec_sensors_data = cros_ec_sensors_read_cmd;
> +
> +	/* Initialize Counter device */
> +	state->counter.name = dev_name(&pdev->dev);
> +	state->counter.parent = &pdev->dev;
> +	state->counter.ops = &cros_ec_sync_ops;
> +	state->counter.counts = cros_ec_sync_counts;
> +	state->counter.num_counts = ARRAY_SIZE(cros_ec_sync_counts);
> +	state->counter.signals = cros_ec_sync_signals;
> +	state->counter.num_signals = ARRAY_SIZE(cros_ec_sync_signals);
> +	state->counter.priv = state;
> +
> +	ret = devm_iio_device_register(dev, indio_dev);
> +	if (ret)
> +		return ret;
> +
> +	return devm_counter_register(dev, &state->counter);
> +}
> +
> +static const struct platform_device_id cros_ec_sync_ids[] = {
> +	{
> +		.name = "cros-ec-sync",
> +	},
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(platform, cros_ec_sync_ids);
> +
> +static struct platform_driver cros_ec_sync_platform_driver = {
> +	.driver = {
> +		.name	= "cros-ec-sync",
> +	},
> +	.probe		= cros_ec_sync_probe,
> +	.id_table	= cros_ec_sync_ids,
> +};
> +module_platform_driver(cros_ec_sync_platform_driver);
> +
> +MODULE_AUTHOR("Gwendal Grignou <gwendal@...omium.org>");
> +MODULE_DESCRIPTION("ChromeOS EC synchronisation sensor driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> index c831915ca7e56..3a15094616710 100644
> --- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> +++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> @@ -31,6 +31,7 @@
>  static char *cros_ec_loc[] = {
>  	[MOTIONSENSE_LOC_BASE] = "base",
>  	[MOTIONSENSE_LOC_LID] = "lid",
> +	[MOTIONSENSE_LOC_CAMERA] = "camera",
>  	[MOTIONSENSE_LOC_MAX] = "unknown",
>  };
>  
> @@ -467,6 +468,20 @@ const struct iio_chan_spec_ext_info cros_ec_sensors_ext_info[] = {
>  };
>  EXPORT_SYMBOL_GPL(cros_ec_sensors_ext_info);
>  
> +const struct iio_chan_spec_ext_info cros_ec_sensors_limited_info[] = {
> +	{
> +		.name = "id",
> +		.shared = IIO_SHARED_BY_ALL,
> +		.read = cros_ec_sensors_id
> +	},
> +	{
> +		.name = "location",
> +		.shared = IIO_SHARED_BY_ALL,
> +		.read = cros_ec_sensors_loc
> +	},
> +	{ },
> +};
> +EXPORT_SYMBOL_GPL(cros_ec_sensors_limited_info);
>  /**
>   * cros_ec_sensors_idx_to_reg - convert index into offset in shared memory
>   * @st:		pointer to state information for device
> diff --git a/drivers/platform/chrome/cros_ec_sensorhub.c b/drivers/platform/chrome/cros_ec_sensorhub.c
> index b7f2c00db5e1e..e4ae0868d1e06 100644
> --- a/drivers/platform/chrome/cros_ec_sensorhub.c
> +++ b/drivers/platform/chrome/cros_ec_sensorhub.c
> @@ -106,6 +106,9 @@ static int cros_ec_sensorhub_register(struct device *dev,
>  		case MOTIONSENSE_TYPE_ACTIVITY:
>  			name = "cros-ec-activity";
>  			break;
> +		case MOTIONSENSE_TYPE_SYNC:
> +			name = "cros-ec-sync";
> +			break;
>  		default:
>  			dev_warn(dev, "unknown type %d\n",
>  				 sensorhub->resp->info.type);
> diff --git a/include/linux/iio/common/cros_ec_sensors_core.h b/include/linux/iio/common/cros_ec_sensors_core.h
> index 7bc961defa87e..e416b28cf24c7 100644
> --- a/include/linux/iio/common/cros_ec_sensors_core.h
> +++ b/include/linux/iio/common/cros_ec_sensors_core.h
> @@ -114,7 +114,9 @@ int cros_ec_sensors_core_write(struct cros_ec_sensors_core_state *st,
>  			       struct iio_chan_spec const *chan,
>  			       int val, int val2, long mask);
>  
> -/* List of extended channel specification for all sensors */
> +/* List of extended channel specification for all sensors. */
> +extern const struct iio_chan_spec_ext_info cros_ec_sensors_limited_info[];
> +/* Add calibration to set above. */
>  extern const struct iio_chan_spec_ext_info cros_ec_sensors_ext_info[];
>  extern const struct attribute *cros_ec_sensor_fifo_attributes[];
>  

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