Date:   Fri, 6 Oct 2017 14:00:51 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Thierry Escande <thierry.escande@...labora.com>
CC:     Benson Leung <bleung@...omium.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Gwendal Grignou <gwendal@...omium.org>,
        <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] platform/chrome: Add cros_ec_accel_legacy driver

On Thu, 5 Oct 2017 18:02:36 +0200
Thierry Escande <thierry.escande@...labora.com> wrote:

> From: Gwendal Grignou <gwendal@...omium.org>
> 
> Add driver to support older EC firmware that only support deprecated
> ec command. Rely on ACPI memory map register to access sensor
> information.
> Present same interface as the regular cros_ec sensor stack:
> - one iio device per accelerometer
> - use HTML5 axis definition
> - use iio abi units
> - accept calibration calls, but do nothing
> Chrome can use the same code than regular cros_ec sensor stack to
> calculate orientation and lid angle.
> 
> Signed-off-by: Gwendal Grignou <gwendal@...omium.org>
> Signed-off-by: Thierry Escande <thierry.escande@...labora.com>

I think we have the scale wrong - otherwise I'm happy with this.

Jonathan

> ---
>  Documentation/ABI/testing/sysfs-bus-iio-cros-ec |  10 +
>  drivers/iio/accel/Kconfig                       |  11 +
>  drivers/iio/accel/Makefile                      |   2 +
>  drivers/iio/accel/cros_ec_accel_legacy.c        | 420 ++++++++++++++++++++++++
>  4 files changed, 443 insertions(+)
>  create mode 100644 drivers/iio/accel/cros_ec_accel_legacy.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-cros-ec b/Documentation/ABI/testing/sysfs-bus-iio-cros-ec
> index 297b972..0e95c2c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-iio-cros-ec
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-cros-ec
> @@ -16,3 +16,13 @@ Description:
>                  the motion sensor is placed. For example, in a laptop a motion
>                  sensor can be located on the base or on the lid. Current valid
>  		values are 'base' and 'lid'.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/id
> +Date:		Septembre 2017
> +KernelVersion:	4.14
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		This attribute is exposed by the CrOS EC legacy accelerometer
> +		driver and represents the sensor ID as exposed by the EC. This
> +		ID is used by the Android sensor service hardware abstraction
> +		layer (sensor HAL) through the Android container on ChromeOS.

Hohum... Still not that keen, but what the heck it is device specific and
hardly a big burden to maintain going forward...

> diff --git a/drivers/iio/accel/Kconfig b/drivers/iio/accel/Kconfig
> index 15de262..5a1ef29 100644
> --- a/drivers/iio/accel/Kconfig
> +++ b/drivers/iio/accel/Kconfig
> @@ -148,6 +148,17 @@ config HID_SENSOR_ACCEL_3D
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called hid-sensor-accel-3d.
>  
> +config IIO_CROS_EC_ACCEL_LEGACY
> +	tristate "ChromeOS EC Legacy Accelerometer Sensor"
> +	select IIO_BUFFER
> +	select IIO_TRIGGERED_BUFFER
> +	select CROS_EC_LPC_REGISTER_DEVICE
> +	help
> +	  Say yes here to get support for accelerometers on Chromebook using
> +	  legacy EC firmware.
> +	  Sensor data is retrieved through IO memory.
> +	  Newer devices should use IIO_CROS_EC_SENSORS.
> +
>  config IIO_ST_ACCEL_3AXIS
>  	tristate "STMicroelectronics accelerometers 3-Axis Driver"
>  	depends on (I2C || SPI_MASTER) && SYSFS
> diff --git a/drivers/iio/accel/Makefile b/drivers/iio/accel/Makefile
> index 31fba19..fdd054a 100644
> --- a/drivers/iio/accel/Makefile
> +++ b/drivers/iio/accel/Makefile
> @@ -43,6 +43,8 @@ obj-$(CONFIG_SCA3000)		+= sca3000.o
>  obj-$(CONFIG_STK8312)		+= stk8312.o
>  obj-$(CONFIG_STK8BA50)		+= stk8ba50.o
>  
> +obj-$(CONFIG_IIO_CROS_EC_ACCEL_LEGACY) += cros_ec_accel_legacy.o
> +
>  obj-$(CONFIG_IIO_SSP_SENSORS_COMMONS) += ssp_accel_sensor.o
>  
>  obj-$(CONFIG_IIO_ST_ACCEL_3AXIS) += st_accel.o
> diff --git a/drivers/iio/accel/cros_ec_accel_legacy.c b/drivers/iio/accel/cros_ec_accel_legacy.c
> new file mode 100644
> index 0000000..26a2ed1
> --- /dev/null
> +++ b/drivers/iio/accel/cros_ec_accel_legacy.c
> @@ -0,0 +1,420 @@
> +/*
> + * Driver for older Chrome OS EC accelerometer
> + *
> + * Copyright 2017 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 memory mapper cros-ec interface to communicate
> + * with the Chrome OS EC about accelerometer data.
> + * Accelerometer access is presented through iio sysfs.
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/kfifo_buf.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/kernel.h>
> +#include <linux/mfd/cros_ec.h>
> +#include <linux/mfd/cros_ec_commands.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/sysfs.h>
> +#include <linux/platform_device.h>
> +
> +#define DRV_NAME	"cros-ec-accel-legacy"
> +
> +/* Indices for EC sensor values. */
> +enum {
> +	X,
> +	Y,
> +	Z,
> +	MAX_AXIS,
> +};
> +
> +/* State data for cros_ec_accel_legacy iio driver. */
> +struct cros_ec_accel_legacy_state {
> +	struct cros_ec_device *ec;
> +
> +	/*
> +	 * Array holding data from a single capture. 2 bytes per channel
> +	 * for the 3 channels plus the timestamp which is always last and
> +	 * 8-bytes aligned.
> +	 */
> +	s16 capture_data[8];
> +	s8 sign[MAX_AXIS];
> +	u8 sensor_num;
> +};
> +
> +static int ec_cmd_read_u8(struct cros_ec_device *ec, unsigned int offset,
> +			  u8 *dest)
> +{
> +	return ec->cmd_readmem(ec, offset, 1, dest);
> +}
> +
> +static int ec_cmd_read_u16(struct cros_ec_device *ec, unsigned int offset,
> +			   u16 *dest)
> +{
> +	u16 tmp;
> +	int ret = ec->cmd_readmem(ec, offset, 2, &tmp);
> +
> +	*dest = le16_to_cpu(tmp);
> +
> +	return ret;
> +}
> +
> +/**
> + * read_ec_until_not_busy() - Read from EC status byte until it reads not busy.
> + * @st: Pointer to state information for device.
> + *
> + * This function reads EC status until its busy bit gets cleared. It does not
> + * wait indefinitely and returns -EIO if the EC status is still busy after a
> + * few hundreds milliseconds.
> + *
> + * Return: 8-bit status if ok, -EIO on error
> + */
> +static int read_ec_until_not_busy(struct cros_ec_accel_legacy_state *st)
> +{
> +	struct cros_ec_device *ec = st->ec;
> +	u8 status;
> +	int attempts = 0;
> +
> +	ec_cmd_read_u8(ec, EC_MEMMAP_ACC_STATUS, &status);
> +	while (status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) {
> +		/* Give up after enough attempts, return error. */
> +		if (attempts++ >= 50)
> +			return -EIO;
> +
> +		/* Small delay every so often. */
> +		if (attempts % 5 == 0)
> +			msleep(25);
> +
> +		ec_cmd_read_u8(ec, EC_MEMMAP_ACC_STATUS, &status);
> +	}
> +
> +	return status;
> +}
> +
> +/**
> + * read_ec_accel_data_unsafe() - Read acceleration data from EC shared memory.
> + * @st:        Pointer to state information for device.
> + * @scan_mask: Bitmap of the sensor indices to scan.
> + * @data:      Location to store data.
> + *
> + * This is the unsafe function for reading the EC data. It does not guarantee
> + * that the EC will not modify the data as it is being read in.
> + */
> +static void read_ec_accel_data_unsafe(struct cros_ec_accel_legacy_state *st,
> +				      unsigned long scan_mask, s16 *data)
> +{
> +	int i = 0;
> +	int num_enabled = bitmap_weight(&scan_mask, MAX_AXIS);
> +
> +	/* Read all sensors enabled in scan_mask. Each value is 2 bytes. */
> +	while (num_enabled--) {
> +		i = find_next_bit(&scan_mask, MAX_AXIS, i);
> +		ec_cmd_read_u16(
> +			st->ec,
> +			EC_MEMMAP_ACC_DATA +
> +				sizeof(s16) *
> +				(1 + i + st->sensor_num * MAX_AXIS),
> +			data);
> +		*data *= st->sign[i];
> +		i++;
> +		data++;
> +	}
> +}
> +
> +/**
> + * read_ec_accel_data() - Read acceleration data from EC shared memory.
> + * @st:        Pointer to state information for device.
> + * @scan_mask: Bitmap of the sensor indices to scan.
> + * @data:      Location to store data.
> + *
> + * This is the safe function for reading the EC data. It guarantees that
> + * the data sampled was not modified by the EC while being read.
> + *
> + * Return: 0 if ok, -ve on error
> + */
> +static int read_ec_accel_data(struct cros_ec_accel_legacy_state *st,
> +			      unsigned long scan_mask, s16 *data)
> +{
> +	u8 samp_id = 0xff;
> +	u8 status = 0;
> +	int ret;
> +	int attempts = 0;
> +
> +	/*
> +	 * Continually read all data from EC until the status byte after
> +	 * all reads reflects that the EC is not busy and the sample id
> +	 * matches the sample id from before all reads. This guarantees
> +	 * that data read in was not modified by the EC while reading.
> +	 */
> +	while ((status & (EC_MEMMAP_ACC_STATUS_BUSY_BIT |
> +			  EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK)) != samp_id) {
> +		/* If we have tried to read too many times, return error. */
> +		if (attempts++ >= 5)
> +			return -EIO;
> +
> +		/* Read status byte until EC is not busy. */
> +		ret = read_ec_until_not_busy(st);
> +		if (ret < 0)
> +			return ret;
> +		status = ret;
> +
> +		/*
> +		 * Store the current sample id so that we can compare to the
> +		 * sample id after reading the data.
> +		 */
> +		samp_id = status & EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK;
> +
> +		/* Read all EC data, format it, and store it into data. */
> +		read_ec_accel_data_unsafe(st, scan_mask, data);
> +
> +		/* Read status byte. */
> +		ec_cmd_read_u8(st->ec, EC_MEMMAP_ACC_STATUS, &status);
> +	}
> +
> +	return 0;
> +}
> +
> +static int cros_ec_accel_legacy_read(struct iio_dev *indio_dev,
> +				     struct iio_chan_spec const *chan,
> +				     int *val, int *val2, long mask)
> +{
> +	struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);
> +	s16 data = 0;
> +	int ret = IIO_VAL_INT;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = read_ec_accel_data(st, (1 << chan->scan_index), &data);
> +		if (ret)
> +			return ret;
> +		*val = data;
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		/* Sensor scale hard coded at 10 bits per g. */
> +		*val = 0;
> +		*val2 = IIO_G_TO_M_S_2(1024);

Just noticed that this looks a little odd.. Scale is the value in m/s^2
that 1LSB equals.  Here we have roughly 0.010045

So you are saying that 1024 counts is 9.81m/s^2  this is near 10.28 m/s I think.
So I think you have that backwards...
We need something like.
*val = IIO_G_TO_MS_2(1)
*val2 = 1024
return IIO_VAL_FRACTIONAL;

Or you could map the 1024 the other way if that works better for precision.

*val = 1;
*val2 = IIO_M_S_2_TO_G(1024)
return IIO_VAL_FRACTIONAL;

which with perfectish maths is 0.009580 * 1024 = 9.81



> +		return IIO_VAL_INT_PLUS_MICRO;
> +	case IIO_CHAN_INFO_CALIBBIAS:
> +		/* Calibration not supported. */
> +		*val = 0;
> +		return IIO_VAL_INT;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int cros_ec_accel_legacy_write(struct iio_dev *indio_dev,
> +				      struct iio_chan_spec const *chan,
> +				      int val, int val2, long mask)
> +{
> +	/*
> +	 * Do nothing but don't return an error code to allow calibration
> +	 * script to work.
> +	 */
> +	if (mask == IIO_CHAN_INFO_CALIBBIAS)
> +		return 0;
> +
> +	return -EINVAL;
> +}
> +
> +static const struct iio_info cros_ec_accel_legacy_info = {
> +	.read_raw = &cros_ec_accel_legacy_read,
> +	.write_raw = &cros_ec_accel_legacy_write,
> +	.driver_module = THIS_MODULE,
> +};
> +
> +/**
> + * cros_ec_accel_legacy_capture() - The trigger handler function
> + * @irq: The interrupt number.
> + * @p:   Private data - always a pointer to the poll func.
> + *
> + * On a trigger event occurring, if the pollfunc is attached then this
> + * handler is called as a threaded interrupt (and hence may sleep). It
> + * is responsible for grabbing data from the device and pushing it into
> + * the associated buffer.
> + *
> + * Return: IRQ_HANDLED
> + */
> +static irqreturn_t cros_ec_accel_legacy_capture(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);
> +
> +	/* Clear capture data. */
> +	memset(st->capture_data, 0, sizeof(st->capture_data));
> +
> +	/*
> +	 * Read data based on which channels are enabled in scan mask. Note
> +	 * that on a capture we are always reading the calibrated data.
> +	 */
> +	read_ec_accel_data(st, *indio_dev->active_scan_mask, st->capture_data);
> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, (void *)st->capture_data,
> +					   iio_get_time_ns(indio_dev));
> +
> +	/*
> +	 * Tell the core we are done with this trigger and ready for the
> +	 * next one.
> +	 */
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static char *cros_ec_accel_legacy_loc_strings[] = {
> +	[MOTIONSENSE_LOC_BASE] = "base",
> +	[MOTIONSENSE_LOC_LID] = "lid",
> +	[MOTIONSENSE_LOC_MAX] = "unknown",
> +};
> +
> +static ssize_t cros_ec_accel_legacy_loc(struct iio_dev *indio_dev,
> +					uintptr_t private,
> +					const struct iio_chan_spec *chan,
> +					char *buf)
> +{
> +	struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%s\n",
> +		       cros_ec_accel_legacy_loc_strings[st->sensor_num +
> +							MOTIONSENSE_LOC_BASE]);
> +}
> +
> +static ssize_t cros_ec_accel_legacy_id(struct iio_dev *indio_dev,
> +				       uintptr_t private,
> +				       const struct iio_chan_spec *chan,
> +				       char *buf)
> +{
> +	struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%d\n", st->sensor_num);
> +}
> +
> +static const struct iio_chan_spec_ext_info cros_ec_accel_legacy_ext_info[] = {
> +	{
> +		.name = "id",
> +		.shared = IIO_SHARED_BY_ALL,
> +		.read = cros_ec_accel_legacy_id,
> +	},
> +	{
> +		.name = "location",
> +		.shared = IIO_SHARED_BY_ALL,
> +		.read = cros_ec_accel_legacy_loc,
> +	},
> +	{ }
> +};
> +
> +#define CROS_EC_ACCEL_LEGACY_CHAN(_axis)				\
> +	{								\
> +		.type = IIO_ACCEL,					\
> +		.channel2 = IIO_MOD_X + (_axis),			\
> +		.modified = 1,					        \
> +		.info_mask_separate =					\
> +			BIT(IIO_CHAN_INFO_RAW) |			\
> +			BIT(IIO_CHAN_INFO_CALIBSCALE) |			\
> +			BIT(IIO_CHAN_INFO_CALIBBIAS),			\
> +		.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SCALE),	\
> +		.ext_info = cros_ec_accel_legacy_ext_info,		\
> +		.scan_type = {						\
> +			.sign = 's',					\
> +			.realbits = 16,					\
> +			.storagebits = 16,				\
> +		},							\
> +	}								\
> +
> +static struct iio_chan_spec ec_accel_channels[] = {
> +	CROS_EC_ACCEL_LEGACY_CHAN(X),
> +	CROS_EC_ACCEL_LEGACY_CHAN(Y),
> +	CROS_EC_ACCEL_LEGACY_CHAN(Z),
> +	IIO_CHAN_SOFT_TIMESTAMP(MAX_AXIS)
> +};
> +
> +static int cros_ec_accel_legacy_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct cros_ec_dev *ec = dev_get_drvdata(dev->parent);
> +	struct cros_ec_sensor_platform *sensor_platform = dev_get_platdata(dev);
> +	struct iio_dev *indio_dev;
> +	struct cros_ec_accel_legacy_state *state;
> +	int ret, i;
> +
> +	if (!ec || !ec->ec_dev) {
> +		dev_warn(&pdev->dev, "No EC device found.\n");
> +		return -EINVAL;
> +	}
> +
> +	if (!ec->ec_dev->cmd_readmem) {
> +		dev_warn(&pdev->dev, "EC does not support direct reads.\n");
> +		return -EINVAL;
> +	}
> +
> +	indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*state));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, indio_dev);
> +	state = iio_priv(indio_dev);
> +	state->ec = ec->ec_dev;
> +	state->sensor_num = sensor_platform->sensor_num;
> +
> +	indio_dev->dev.parent = dev;
> +	indio_dev->name = pdev->name;
> +	indio_dev->channels = ec_accel_channels;
> +	/*
> +	 * Present the channel using HTML5 standard:
> +	 * need to invert X and Y and invert some lid axis.
> +	 */
> +	for (i = X ; i < MAX_AXIS; i++) {
> +		switch (i) {
> +		case X:
> +			ec_accel_channels[X].scan_index = Y;
> +		case Y:
> +			ec_accel_channels[Y].scan_index = X;
> +		case Z:
> +			ec_accel_channels[Z].scan_index = Z;
> +		}
> +		if (state->sensor_num == MOTIONSENSE_LOC_LID && i != Y)
> +			state->sign[i] = -1;
> +		else
> +			state->sign[i] = 1;
> +	}
> +	indio_dev->num_channels = ARRAY_SIZE(ec_accel_channels);
> +	indio_dev->dev.parent = &pdev->dev;
> +	indio_dev->info = &cros_ec_accel_legacy_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +
> +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> +					      cros_ec_accel_legacy_capture,
> +					      NULL);
> +	if (ret)
> +		return ret;
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}
> +
> +static struct platform_driver cros_ec_accel_platform_driver = {
> +	.driver = {
> +		.name	= DRV_NAME,
> +	},
> +	.probe		= cros_ec_accel_legacy_probe,
> +};
> +module_platform_driver(cros_ec_accel_platform_driver);
> +
> +MODULE_DESCRIPTION("ChromeOS EC legacy accelerometer driver");
> +MODULE_AUTHOR("Gwendal Grignou <gwendal@...omium.org>");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:" DRV_NAME);

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