Solution 10 concurrency and synchronization - #146
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This starts development of driver for gyroscope & accelerometer mpu6050. Some documentation for the device is attached. Signed-off-by: Aleksandr Bulyshchenko <A.Bulyshchenko@globallogic.com>
Driver skeleton consist of two functions: 1. Module entry point (mpu6050_init) This function is called when driver is loaded. Should return 0 on success (driver will be loaded) or negative error value on failure (driver will not be loaded). 2. Module exit point (mpu6050_exit) This function is called on driver removal. No return value. Both functions should be exported using module_init and module_exit macroses. Debug information may be printed using printk() function and can be read using dmesg program. But checkpatch.pl script treat printk(KERN_INFO as warnings so pr_info() was used instead. Signed-off-by: Andriy.Khulap <andriy.khulap@globallogic.com>
I2C driver consist of:
1. probe and remove functions. Called on driver load and removal respectively.
2. i2c_device_id structure. Should contain strings exact equal to devive tree.
MODULE_DEVICE_TABLE() macro is mandatory for match with dtb. Without it
driver will not be probed.
static const struct i2c_device_id mpu6050_idtable [] = {
{ "mpu6050", 0 },
{ }
};
MODULE_DEVICE_TABLE(i2c, mpu6050_idtable);
3. i2c_driver structure itself.
Important fields: probe, remove and id_table should point to items described
above.
static struct i2c_driver mpu6050_i2c_driver = {
.driver = {
.name = "gl_mpu6050",
},
.probe = mpu6050_probe ,
.remove = mpu6050_remove,
.id_table = mpu6050_idtable,
};
I2C driver is created using i2c_add_driver(&mpu6050_i2c_driver) function.
It will return 0 on success and most likely is called from module_init().
Please note that without device tree match probe function will not be called,
but i2c_add_driver() will return OK. With device tree match, probe function
will be called right after i2c_add_driver().
I2C driver is removed with i2c_del_driver(&mpu6050_i2c_driver) function.
If driver was created, remove function will be called.
Signed-off-by: Andriy.Khulap <andriy.khulap@globallogic.com>
Most of i2c chips have a special read-only register with unique id. So the easiest way to communicate with the device is to read that register. It should be accessibe even during power off modes and so failing to read it means no communication with the device. Reading non-expected value will indicate wrong adress or data size used, or incorrect device connected (other revision). Reading small amounts of data is easiest done using i2c_smbus_read_byte() or similar functions. Why smbus? Because they are wrappers to i2c_transfer() function and have internal device address as a parameter. This eliminates need to fill i2c_transfer structure for each small read or write. Using i2c_transfer() should be considered for large blocks of data and gives a performance boost over i2c_smbus wrappers. Signed-off-by: Andriy.Khulap <andriy.khulap@globallogic.com>
This mpu6050 driver functionality consist of reading relevant values and exporting them to the user space. Needed parameters are: accelerometer x, y, z, gyroscope x, y, z and temperature (as an easiest check that device is configured and operating properly). First, the chip must be configured. This consist of programming all setup registers with correct values. For example: clear power down, set prescalers, configures fifos and so on. Configuration is usually done in driver probe routine. Second, reading values or performing needed actions can be done in a separate theread inside driver, or in the workqueue. But this driver is supposed to give values on demand so there is no need for that. All values are read at once in a single function. To export data to the user space was decided to use sysfs. A class was created and 7 attributes for each parameter. Since all parameters are read-only, all attributes have only show function and their access rights are set to 0444. So all _show() fuctions are almost the same: read all parameters first, then return the needed one. The summary how this driver works: 1. Create i2c device in module_init() and configure the chip from i2c_probe(). 2. Create sysfs class and attributes for each parameter from module_init(). 3. Read and return mpu6050 parameters in each sysfs_attribute_x_show(). Signed-off-by: Andriy.Khulap <andriy.khulap@globallogic.com>
Signed-off-by: Yevgen Kovalyov <yevgen.kovalyov@globallogic.com>
Signed-off-by: Aleksandr Bulyshchenko <A.Bulyshchenko@globallogic.com>
The module adds support for the device tree, multiple devices, work with streams and synchronization mechanisms Signed-off-by: Andrey Pahomov <pahomov.and@gmail.com>
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Signed-off-by: Andrey Pahomov <pahomov.and@gmail.com>
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To build the module, a script with setting environment variables has been added:
./build.sh
To check multithreading, you can run the following command in the terminal:
cat /sys/class/i2c-dev/i2c-0/device/0-0068/temp &
cat /sys/class/i2c-dev/i2c-0/device/0-0068/accel_xyz &
cat /sys/class/i2c-dev/i2c-0/device/0-0068/gyro_xyz &