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Date:	Thu, 7 Jul 2011 18:25:57 -0700
From:	Nathan Royer <nroyer@...ensense.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Jonathan Cameron <jic23@....ac.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Jiri Kosina <jkosina@...e.cz>,
	Jean Delvare <khali@...ux-fr.org>,
	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
	Chris Hudson <chudson@...nix.com>, eric.andersson@...xphere.com
Subject: RE: [PATCH 01/11] misc: inv_mpu primary header file and README file.

> Its hard to judge with what has been explained so far but the device
> appears to be very different in the two operating modes so it might
> make
> sense to have it as two drivers (or one driver with two very distinct
> modes)

I'm thinking two distinct drivers.  One we should call the MPU controller
and the other the gyro driver.

Comparing it to the i2c architecture.  In the board file, each i2c bus is
initialized with information about each device on the bus.  An i2c_client
is created for each device and their probe functions called allowing the
driver to use the i2c_client to communicate with the device.

For the MPU controller, it would be similar registration, but the slaves
would be given to the MPU controller to control.  In the board file the
MPU controller would be initialized with which devices that it should
control.  The MPU controller would then probe each device for the
interface used to control it.  If that device is not probed then it should
act alone, otherwise it should allow the MPU controller to control it.

Regarding the interface, I'm still confused on how to resolve the
iio/input decision.  Should the devices use both?  I think the final
interface would be a combination of possibly all 3 interfaces, misc,
input, and iio.

Below is a discussion of the IOCTL's, how they are currently used, and how
I'm thinking about mapping them in between the 3 interfaces.

Our MPL needs the platform data, mostly the orientation of each device.
The relevant information can be made available as iio sysfs attributes for
each device. ========================================
#define MPU_GET_EXT_SLAVE_PLATFORM_DATA	\
	_IOWR(MPU_IOCTL, 0x02, struct ext_slave_platform_data)
#define MPU_GET_MPU_PLATFORM_DATA	\
	_IOWR(MPU_IOCTL, 0x02, struct mpu_platform_data)
#define MPU_GET_EXT_SLAVE_DESCR	\
	_IOWR(MPU_IOCTL, 0x02, struct ext_slave_descr)

These are simple register reads and register writes.  These can be
replaced with iio sysfs attributes for the gyro driver.
=======================================
#define MPU_READ		_IOWR(MPU_IOCTL, 0x10, struct
mpu_read_write)
#define MPU_WRITE		_IOW(MPU_IOCTL,  0x10, struct
mpu_read_write)

The following is used to interact at runtime with the DMP.  These will
need to remain as ioctls to drivers/misc/inv_mpu
========================================
#define MPU_READ_MEM		_IOWR(MPU_IOCTL, 0x11, struct
mpu_read_write)
#define MPU_WRITE_MEM		_IOW(MPU_IOCTL,  0x11, struct
mpu_read_write)
#define MPU_READ_FIFO		_IOWR(MPU_IOCTL, 0x12, struct
mpu_read_write)
#define MPU_WRITE_FIFO		_IOW(MPU_IOCTL,  0x12, struct
mpu_read_write)

These were used for reading raw data from each slave.  These can be
replaced by an appropriate IIO interface for raw data, implemented
separately by each slave driver.  Input can be then used for calibrated
data and can be fed back via uinput from user space.
========================================
#define MPU_READ_COMPASS	_IOR(MPU_IOCTL, 0x12, __u8)
#define MPU_READ_ACCEL		_IOR(MPU_IOCTL, 0x13, __u8)
#define MPU_READ_PRESSURE	_IOR(MPU_IOCTL, 0x14, __u8)

These are used to configure each slave.  These can be replaced by sysfs
attributes implemented by each slave driver in iio.
========================================================
#define MPU_CONFIG_GYRO		_IOW(MPU_IOCTL, 0x20, struct
ext_slave_config)
#define MPU_CONFIG_ACCEL	_IOW(MPU_IOCTL, 0x21, struct
ext_slave_config)
#define MPU_CONFIG_COMPASS	_IOW(MPU_IOCTL, 0x22, struct
ext_slave_config)
#define MPU_CONFIG_PRESSURE	_IOW(MPU_IOCTL, 0x23, struct
ext_slave_config)

#define MPU_GET_CONFIG_GYRO	_IOWR(MPU_IOCTL, 0x20, struct
ext_slave_config)
#define MPU_GET_CONFIG_ACCEL	_IOWR(MPU_IOCTL, 0x21, struct
ext_slave_config)
#define MPU_GET_CONFIG_COMPASS	_IOWR(MPU_IOCTL, 0x22, struct
ext_slave_config)
#define MPU_GET_CONFIG_PRESSURE	_IOWR(MPU_IOCTL, 0x23, struct
ext_slave_config)

This was used to start or stop the system.  This can be replaced with iio
sysfs power mode attribute for each slave, and an additional one for the
MPU controller.
=========================================
#define MPU_SUSPEND		_IOW(MPU_IOCTL, 0x30, __u32)
#define MPU_RESUME		_IOW(MPU_IOCTL, 0x31, __u32)

Selecting on /dev/mpu will return a MPU_PM_EVENT_SUSPEND_PREPARE or
MPU_PM_EVENT_POST_SUSPEND allowing user space to decide if it wants to
leave anything powered on when suspended.  This in conjunction with the
IGNORE_SYSTEM_SUSPEND allows the DMP plus gyro and/or accel to continue
running while the main processor is suspended.  This can be used to wake
up the main processor on a particular motion event, or to record motion
events to be reported when the processor later wakes up.  This ioctl
signals that user space has finished configuring all sensors and the MPU
controller and that the MPU controller can continue.
=======================================
#define MPU_PM_EVENT_HANDLED	_IO(MPU_IOCTL, 0x32)

Requested sensors is a common place to know which sensors are on, and to
specify which sensors to turn on the next time the system is started.
This can be removed since it is redundant with power mode attributes I'm
proposing be used by each slave and the MPU controller.
=======================================
#define MPU_GET_REQUESTED_SENSORS	_IOR(MPU_IOCTL, 0x40, __u8)
#define MPU_SET_REQUESTED_SENSORS	_IOW(MPU_IOCTL, 0x40, __u8)

See my note on MPU_PM_EVENT_HANDLED above.  This can be made a SysFs
attribute of drivers/misc/inv_mpu
=======================================
#define MPU_GET_IGNORE_SYSTEM_SUSPEND	_IOR(MPU_IOCTL, 0x41, __u8)
#define MPU_SET_IGNORE_SYSTEM_SUSPEND	_IOW(MPU_IOCTL, 0x41, __u8)

These are bitfield of how the MPU controller state.  Which devices are
currently suspended, which devices are running, if the i2c master is
bypassed, if the DMP is running.  This can be made a SysFs attribute, and
perhaps removed.
=======================================
#define MPU_GET_MLDL_STATUS		_IOR(MPU_IOCTL, 0x42, __u8)

This is a bitfield showing the status of which of the master i2c channels
have been enabled.  The mpu3050 has 1 channel, and the mpu6050 has 5
channels.  This can become a sysfs attribute
=======================================
#define MPU_GET_I2C_SLAVES_ENABLED	_IOR(MPU_IOCTL, 0x43, __u8)

After all is said and done this is files that would be made available:
/dev/mpu
	Iotcl interface for memory and fifo reads writes, read for events
include pm events and irq events.

/sys/bus/iio/devices/device[ACCEL]/power_state
/sys/bus/iio/devices/device[ACCEL]/accel_x_raw
/sys/bus/iio/devices/device[ACCEL]/accel_y_raw
/sys/bus/iio/devices/device[ACCEL]/accel_z_raw
/sys/bus/iio/devices/device[ACCEL]/<other attributes as appropriate>

/sys/bus/iio/devices/device[MAGN]/power_state
/sys/bus/iio/devices/device[MAGN]/magn_x_raw
/sys/bus/iio/devices/device[MAGN]/magn_y_raw
/sys/bus/iio/devices/device[MAGN]/magn_z_raw
/sys/bus/iio/devices/device[MAGN]/<other attributes as appropriate>

/sys/bus/iio/devices/device[GYRO]/power_state
/sys/bus/iio/devices/device[GYRO]/gyro_x_raw
/sys/bus/iio/devices/device[GYRO]/gyro_y_raw
/sys/bus/iio/devices/device[GYRO]/gyro_z_raw
/sys/bus/iio/devices/device[GYRO]/<other attributes as appropriate>

Then for input ABS_X, ABS_Y and ABS_Z for each of the sensors containing
calibrated data.  There are a number of other computed data values we
would want to make available, but these can also be made available in user
space by the MPL if necessary.

> Can the slave interface appears to be an i瞔 bus too or is the
> interface
> too different (ie could the smart mode create an i瞔 bus that it uses
> to
> talk to the drivers to configure them for 'smart' mode)

I'm not exactly sure of the details of what you are suggesting, but
somehow telling a slave that it is now being used in 'smart' mode is fine,
as long as the MPU controller can still read back the information it needs
to control it, for example setting up the mpu3050 i2c master.

> I'm not entirely sure at this point I understand quite how all the
> pieces
> fit together.

It is a fairly complicated system, and why I want to get a good idea of
what we want long term before working on further changes.
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