Long story short: the probe() function of the driver is called as a result of calling the register_driver for that specific bus. More precisely, it’s called by the probe() of that bus_type structure. In your case: i2c_bus_type. Here’s the call chain in your I2C case: i2c_register_driver driver_register bus_add_driver driver_attach __driver_attach (for your device) driver_probe_device really_probe … Read more
Your references are good but lack a definition of what is a platform device. There is one on LWN. What we can learn from this page: Platform devices are inherently not discoverable, i.e. the hardware cannot say “Hey! I’m present!” to the software. Typical examples are i2c devices, kernel/Documentation/i2c/instantiating-devices states: Unlike PCI or USB devices, … Read more
To be able to control wireless drivers from userspace, some IPC communication processes between kernel and userspace are used. At first ioctl with vendor dependent APIs was used. In 1996, Jean Tourrilhes creates wireless extensions (WE or WEXT). The Wireless Extension (WE) is a generic API allowing a driver to expose to the user space … Read more
The correct command is just rm 🙂 A device node created by mknod is just a file that contains a device major and minor number. When you access that file the first time, Linux looks for a driver that advertises that major/minor and loads it. Your driver then handles all I/O with that file. When … Read more
Not all virtual (linear) addresses must be mapped to anything. If the code accesses unmapped page, the page fault is risen. The physical page can be mapped to several virtual addresses simultaneously. In the 4 GB virtual memory there are 2 sections: 0x0… 0xbfffffff – is process virtual memory and 0xc0000000 .. 0xffffffff is a … Read more
After reading kernel source I finally managed to make netlink sockets work for me. Below is an example of Netlink socket basics i.e opening a netlink socket, reading and writing to it and closing it. Kernel Module #include <linux/module.h> #include <net/sock.h> #include <linux/netlink.h> #include <linux/skbuff.h> #define NETLINK_USER 31 struct sock *nl_sk = NULL; static void … Read more
First, start by writing a generic kernel module. There are multiple places to look up for information but I found this link to be very useful. After you have gone through all examples specified there you can start writing your own Linux Driver Module. Please note, that you will not get away with just copy-pasting … Read more
**TODO** +editPic: Linux Kernel Developer -> (Ring Layer 0) +addSection: Kernel Virtualization Engine KERN_WARN_CODING_STYLE: Do not Loop unless you absolutely have to. Recommended Books for the Uninitialized void *i “Men do not understand books until they have a certain amount of life, or at any rate no man understands a deep book, until he has … Read more
From the kernel’s perspective, see /usr/src/linux/Documentation/firmware_class/README: kernel(driver): calls request_firmware(&fw_entry, $FIRMWARE, device) userspace: – /sys/class/firmware/xxx/{loading,data} appear. – hotplug gets called with a firmware identifier in $FIRMWARE and the usual hotplug environment. – hotplug: echo 1 > /sys/class/firmware/xxx/loading kernel: Discard any previous partial load. userspace: – hotplug: cat appropriate_firmware_image > \ /sys/class/firmware/xxx/data kernel: grows a buffer in … Read more
Try using the getconf utility, which will allow you to retrieve the page size, in bytes, easily. getconf PAGESIZE Example output, in bytes: 4096