Situation 1:
I have an i2c chip driver as part of linux kernel. I can verify the i2c chip driver is in the kernel from kernel boot messages (my chip driver is mma8450)
dmesg:
mma8450 0-001c: uevent
I can also see this driver in (0x1c is i2c address of chip)
cat /sys/bus/i2c/devices/0-001c/name
mma8450
I can not see this driver node in /dev interface. My question is how can I create node of this device in /dev so that I can access this device in a user program ?
Situation 2:
I create the module of the same chip driver and does not make it a part of kernel. I can load this module using insmod mma8450, how can I create a node of this device as I don't have its major / minor numbers ? (I can not see major & minor numbers assigned to this driver in mma8450 source code)
Any help is appreciated
Regards
Load the kernel module:
modprobe i2c-dev
ls /dev/i2*
/dev/i2c-0
/dev/i2c-10
/dev/i2c-12
/dev/i2c-14
/dev/i2c-3
/dev/i2c-5
/dev/i2c-7
/dev/i2c-9
/dev/i2c-1
/dev/i2c-11
/dev/i2c-13
/dev/i2c-2
/dev/i2c-4
/dev/i2c-6
/dev/i2c-8
Find the major/minor numbers for your device:
cat /proc/devices
You should see a device for the i2c bus and one for the i2c device itself.
Create the device node for the i2c device driver:
mknod /dev/[device name] [type] [major] [minor]
This is 3-Axis Accelerometer. Linux registers it as a driver for input_polled_dev type.
You can uaccess it using /dev/i2c-x bus (controller) device node, but there is no much sense using it that way directly from userspace.
I2C clients are not meant to be used using /dev device nodes.
They should be registered to Kernel I2C framework and used through higher layers API.
There is sample program for reading similar MMA7455L x,y,z registers from userspace using /dev/i2c-X bus device node.
Reading the Accelerometer With I²C
Related
I have a device with SPI bus which is connected via PCIe to a linux machine. I'm developing a simple SPI driver for this device. With spi_register_master I can create a SPI master (it is listed under /sys/class/spi_master/spixxxx).
For accessing the bus I would like to use spidev from the userland, but I have not found a way to register a spidev device at runtime. All ways I have found use the device tree to insert the information into the linux kernel.
Is there some way to create spidevdevicesat runtime?
Edit: I suppose it is the same problem with all protocol drivers and not limited to spidev.
I need to have i2c slave Linux kernel driver for TI AM335x.
I googled about and didn't find precise information.
Should I do everything from scratch, or maybe someone has some reference about it? or even a patch
Thanks
Avner
For new device which connected as slave to i2c bus, you should write neither "i2c driver" nor "driver for AM335x" (as far as the processor support already present in kernel).
i2c is a bus and there is kernel infrastructure for the bus, see documentation.
You should figure out what type your device is and then write driver for this type of device using i2c bus primitives.
For example, the driver for DS13xx and compatible IC is rtc driver.
A driver "for" PCF8574 i2c gpio expander can be GPIO driver as well as keypad driver.
Existing kernel drivers such as xilinx have specific way to be registered (as tty device), if they are mapped directly to cpu memory map as done here with device tree:
https://xilinx-wiki.atlassian.net/wiki/spaces/A/pages/18842249/Uartlite+Driver
But in other cases, there is a PCIe device (like FPGA which has the xilinx uart IPs) which is connected to and the cpu.
How should we make the uart get registered when using PCIe device ?
The device tree I try to register into PCIe is uartlite driver:
https://github.com/Xilinx/linux-xlnx/blob/master/drivers/tty/serial/uartlite.c
I think that what I probably need to do is:
Write a custom pci driver.
Need to prepare platform_device struct and then call the uart probe routine from pci driver:
ulite_probe(struct platform_device *pdev)
I've seen related question with others using FPGA with multiple device connected, but seems that there is no docuemnt, or tutorial which describes how to do this.
Any comment, example or document is appreciated.
So something like a ARM CPU connected to an Artix FPGA over PCIe right?
Yes, you would need a custom PCIe driver. The PCIe configuration and data spaces would have to be mapped. Have a look at pci_resource_{start, len} and pci_remap_bar functions. You can then use pci_get_device to get a pointer to the struct device and retrieve the virtual address of the PCIe configuration space. The UART driver can then use the struct device pointer and it's register map should be at some offset to the virtual address of the PCIe configuration space as per your design. You can invoke the probe call of UARTlite IP driver in your own driver.
"Existing kernel drivers such as xilinx have specific way to be registered (as tty device), if they are mapped directly to cpu memory map as done here with device tree". Note that this is true if we are only talking of tty devices. A GPIO peripheral IP won't be expose as tty but in /sys/class/gpio.
I am currently learning about linux device drivers, specifically for using an i2c device with a beaglebone. I have this LCD with a PCF8574AT on it. Searching through the linux drivers folders, I see that a driver gpio-pcf857x.c already exists.
My question is how do I associate this device with this driver? When I do ls -l /dev the major number for i2c-2 is 89 which is the i2c character driver. How do I change this driver association? What material should I research on this? Also, I can see the slave address when I do i2cdetect so I know it is connected.
Any help is greatly appreciated.
The solution is here for how to instantiate i2c devices in linux
I a noob to Linux device drivers.
I have an IIO driver with me (for OPT3001 ambient light sensor) , operating over the I2C bus, which has been compiled successfully in the kernel (version 3.18). The device tree is modified to match the compatible field, present in the driver.
The problem is how do I access this driver to get some data in the userspace ?
The driver has some callbacks for read and write registered in a structure. Should I call them directly in my C file ?
you have differents possibilities :
your driver provide a /dev node you can open in you C file.
your driver provide informations through sysfs.
in case of a /dev node, you can have access to file operations (open, read, write, ioctl). you just have to open your file 1 time and each read() call will read the value from the sensor.
in case of sysfs, you should find the file to open/read in /sys/class/...
You can use the userspace API provided by:
#include <linux/i2c-dev.h>
Using it you can open de bus /dev/i2c-X (X=0,1,2,...), set device address using ioctl call, and use read and write operations to read and write to/from the bus.
Also, you can install "i2c-tools" package (apt-get install i2c-tools), to install userspace tools like i2cset, i2cget and i2cdetect, very useful for testing the I2C bus and the device connected to it.