I'm trying to learn about device drivers on Linux Kernel, for that I've created three modules with:
A bus type
A device driver
A fake device that does nothing now, only is registered
Everything works fine, I can load the bus, the driver and the module that creates the device. Everything appears on sysfs, including the link between the device and the device driver that indicates that they are binded.
And when the driver and device are loaded, I can see using udevadm monitor that also some events are provoked:
KERNEL[1275564332.144997] add /module/bustest_driver (module)
KERNEL[1275564332.145289] add /bus/bustest/drivers/bustest_example (drivers)
UDEV [1275564332.157428] add /module/bustest_driver (module)
UDEV [1275564332.157483] add /bus/bustest/drivers/bustest_example (drivers)
KERNEL[1275564337.656650] add /module/bustest_device (module)
KERNEL[1275564337.656817] add /devices/bustest_device (bustest)
UDEV [1275564337.658294] add /module/bustest_device (module)
UDEV [1275564337.664707] add /devices/bustest_device (bustest)
But after everything, the device doesn't appear on hal. What else need a device to be seen by hal?
Everything seems to be ok with the device, the problem is that Hal needs a handler for each subsystem (the list of handlers can be found in hald/linux/device.c), and obviously, hal doesn't support bustest, the subsystem invented for this case.
If the bus is registered with the name "pseudo" instead of "bustest", hal uses a set of handlers defined for fake devices to initialize the database entry, registers it and send a DeviceAdded event.
Related
Hi I am new to kernel driver developement. I am using the raspberry pi as my hostI am trying to create an I2C driver for a custom board we have. The custom board will act as the slave. I am confused about how do I go about entering the devices slave address. From what I understand
You need to either have a board setup file which I dont since its a custom board.
You can edit the device tree
Or you can do it in the user space application.
I am not sure where exactly to edit the device tree if I go with the second option. More over I would like to somehow register the slave address in the I2C driver itself. That way I donot need to rebuild the kernel. One method i was looking at was to set the i2c client from the driver code but that was advised by commentators I am not sure why. Any help would be appreciated.
Instantiating Drivers
So I have finally a working way in which I can bind the I2C device without needing a kernel rebuild. I create two driver files(.ko files). One for registering and one for the actual driver.
The way I did it is I got the bus number to which the device was connected.
(You can look into i2c user space code. i2cdetect -y (busnumber) will help you detect which bus number it is)
Once I knew that I created a driver file which would register my device by getting access to the adapter and then registering it. My bus number was 1 and slave address 0x10
static struct i2c_board_info board_info[] __initdata =
{
{
I2C_BOARD_INFO("my_device", 0x10),
},
};
And in the init function of the driver I register the device by
i2c_new_device(i2c_get_adapter(1), board_info[0])
Thats it. Now once you build this insmod the ko file before insmoding the actual driver file and everything should work.
I am a newbie to linux kernel. While interfacing with the external device, I made the required changes in bsp file. The bsp file device name and platform_driver name should match in order to invoke probe(). I have heard that probe will check whether h/w exists and probe() will create device file (/dev/rtc1) for a new external device. I am not sure about the functionality of the probe(). Can someone explain me how device file is created in this context?Thank you in advance!
probe() is a callback function that gets called, irrespective of h/w presence, when the bus_match_driver() routine returns success. The probe function is called when a device is installed that the driver-core thinks it should handle; the probe function should perform checks on the information passed to it about the device and decide whether the driver is really appropriate for that device. A device file is created either manually by mknod or automatically by udev and is not directly related to probe function. The book https://lwn.net/Kernel/LDD3/ (highly recommended) has all the details regarding creating a device node.
From a general standpoint, I am trying to figure out how to access a platform device from userspace. To be more specific, I have a EMIF controller on and SoC of which I have added to my device tree and I believe it is correctly bound to a pre-written EMIF platform device driver. Now I am trying to figure out how I can access this EMIF device from a userspace application. I have come accross a couple different topics that seem to have some connection to this issue but I cannot quite find out how they relate.
1) As I read it seems like most I/O is done through the use of device nodes which are created by mknod(), do I need to create a device node in order to access this device?
2) I have read a couple threads that talk about writting a Kernel module (Character?, Block?) that can interface with both userspace and the platform device driver, and use it as an intermediary.
3) I have read about the possibility of using mmap() to map the memory of my platform device into my virtual memory space. Is this possible?
4) It seems that when the EMIF driver is instantiated, it calls the probe() fucntion. What functions would a userpace application call in the driver?
It's not completely clear what you're needing to do (and I should caveat that I have no experience with EMIF or with "platform devices" specifically), but here's some overview to help you get started:
Yes, the usual way of providing access to a device is via a device node. Usually this access is provided by a character device driver unless there's some more specific way of providing it. Most of the time if an application is talking "directly" to your driver, it's a character device. Most other types of devices are used in interfacing with other kernel subsystems: for example, a block device is typically used to provide access from a file system driver (say) to an underlying disk drive; a network driver provides access to the network from the in-kernel TCP/IP stack, etc.
There are several char device methods or entry points that can be supported by your driver, but the most common are "read" (i.e. if a user-space program opens your device and does a read(2) from it), "write" (analogous for write(2)) and "ioctl" (often used for configuration/administrative tasks that don't fall naturally into either a read or write). Note that mknod(2) only creates the user-space side of the device. There needs to be a corresponding device driver in the kernel (the "major device number" given in the mknod call links the user-space node with the driver).
For actually creating the device node in the file system, this can be automated (i.e. the node will automatically show up in /dev) if you call the right kernel functions while setting up your device. There's a special daemon that gets notifications from the kernel and responds by executing the mknod(2) system call.
A kernel module is merely a dynamically loadable way of creating a driver or other kernel extension. It can create a character, block or network device (et al.), but then so can a statically linked module. There are some differences in capability mostly because not all kernel functions you might want to use are "exported" to (i.e. visible to) dynamically loaded modules.
It's possible to support mapping of the device memory into user virtual memory space. This would be implemented by yet another driver entry point (mmap). See struct file_operations for all the entry points a char driver can support.
This is pretty much up to you: it depends on what the application needs to be able to do. There are many drivers in the kernel that provide no direct function to user-space, only to other kernel code. As to "probe", there are many probe functions defined in various interfaces. In most cases, these are called by the kernel (or perhaps by a 'higher level "class" driver') to allow the specific driver to discover, identify and "claim" individual devices. They (probe functions) don't usually have anything directly to do with providing access from user-space but I might well be missing something in a particular interface.
You need to create a device node in order to access the device.
The probe function is called when the driver finds a matching device.
For information on platform device API, the following articles could be useful.
The platform device API
Platform devices and device trees
I am new to Linux and I need to write a USB driver for a device with 2 interfaces. One interface is HID class (3/0/0) with one interrupt in endpoint and a report descriptor. The other interface is vendor defined with 3 bulk endpoints. In my usb_device_id table I have a USB_DEVICE entry with the VID and PID.
When I plug in the device, my xxx_probe function is called for the vendor defined interface but not for the HID interface. Instead, it appears that a built-in driver called 'generic-usb' is taking control of the HID interface.
Is there a way to ensure that my driver probe function is called first?
Why doesn't Linux make multiple passes looking for a more specific driver first (like Windows does)?
Alternatively, can the 'generic-usb' driver be used to receive data on the interrupt endpoint and to set reports and features on the control pipe?
It appears that libusb-1.0.8 allows an application to take control of interfaces on an attached device without the need of a custom driver. So far it appears to provide all the support that I need.
If a USB device driver is loaded, and at some time the device plugs in, then which part of the kernel will create struct device and register it?
When the driver is loaded, the system calls the function, which you assigned in module_init. You will want to call there usb_register(struct usb_driver skel_driver), where skel_driver is a struct with pointers to methods servicing the device, like the probe method.
The probe method is the one which is called, when a new usb device is introduced in to the system. In this place you can fill your struct (usb_skel) with what you will need in the future, initiate a char device or whatever you do, when the device is introduced.
The system mostly won't create anything by itself, it has to have most of the structs prepared and filled with device specific data.
Please see usb-skeleton in lxr for reference and learn to use it, besides read writing usb drivers from LDD.
Cheers