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--- wiki2:linux_drivers [2019/09/22 06:24]
alfred [Manual binding & unbinding]
+++ wiki2:linux_drivers [2020/09/11 20:57] (actual)
@@ Línea 28: / Línea 28: @@
 depmod creates a list of module dependencies by reading each module underlib/modules/version and determining what symbols it exports and what symbols it needs. By default, this list is written to modules.dep, and a binary hashed version namedmodules.dep.bin, in the same directory.
-==== Helper functions ====
-  * ''printk()'' is the equivalent of printf() for kernel modules.
 ==== Structure ====
 A device driver contains at least two functions:
@@ Línea 57: / Línea 55: @@
 MODULE _DESCRIPTION (" Test Driver Module ");
 </code>
+It's required that the MODULE_LICENSE macro receives a GPL license.
 ==== Compilation ====
 To build a module or driver, you need to have the kernel source (or, at least, the kernel headers) installed on your system. The kernel source is assumed to be installed at /usr/src/linux. If it’s at
@@ Línea 101: / Línea 99: @@
+===== Useful functions and interfaces in Kernel =====
+==== Helper functions ====
+  * ''printk()'' is the equivalent of printf() for kernel modules.
+''pr_*()'' functions are the same as plain printk(), but with the KERN_xxx log level already included.
+''dev_*()'' functions (like ''dev_alert'' or ''dev_info'') are the same as the corresponding pr_*() functions, but also print identifying information about the struct device.
+<code>
+dev_info(&hdev->dev, "VEIKK A15 has been attached\n");
+dev_alert(&hdev->dev, "It failed on allockating memory for the VEIKK A15\n");
+</code>
+==== Allocating memory ====
+''kzalloc()'' allocates kernel memory like ''kmalloc()'', but it also zero-initializes the allocated memory. ''devm_kzalloc()'' is managed ''kzalloc()''. The memory allocated with managed functions is associated with the device. When the device is detached from the system or the driver for the device is unloaded, that memory is freed automatically.
+The memory allocated with ''kzalloc()'' should be freed with ''kfree()''. The memory allocated with ''devm_kzalloc()'' is freed automatically. It can be freed with ''devm_kfree()''.
+''hid_set_drvdata'' \\
+Will set on the data property from the hdev the passed value.
+''hid_parse(hdev)'' \\
+Required to be called after setting up the device. It parses a report description of the device and populate fields of the HID device struct (necessary for hid_hw_start()).
+For device memory allocations there is also a "group" concept. Groups can be thought of as markers in the stream of allocations associated with a given device. The allocations performed within a specific group can be rolled back without affecting any others. In brief, the group API is:
+<code>
+    void *devres_open_group(struct device *dev, void *id, gfp_t gfp);
+    void devres_close_group(struct device *dev, void *id);
+    void devres_remove_group(struct device *dev, void *id);
+    int devres_release_group(struct device *dev, void *id);
+</code>
 ===== USB =====
@@ Línea 123: / Línea 153: @@
 echo -n "0003:2FEB:0004.0007" > /sys/bus/hid/drivers/veikk/bind
 </code>
+Reference: https://lwn.net/Articles/143397/
 ===== Resources =====
 Tutorial for creating a driver for a virtual char device. It creates that device using ''mknod''  command and accesses it using the driver. \\
-https://s3.wasabisys.com/public-files/tutorial-DD.pdf
+https://s3.wasabisys.com/my-files/public/tutorial-DD.pdf
+----
+===== How to... Graphic tablet =====
+To see all registered inputs:
+<code>
+xinput
+</code>
+To map a xinput with a display (''xrandr'' will give you the display id):
+<code>
+ xinput map-to-output <registered input id> <display id>
+ xinput map-to-output 22 HDMI-1-1
+</code>
+==== List USB devices ====
+To detect your USB device, in a terminal, you can try:
+<code>
+lsusb , example:
+$ lsusb
+Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
+Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
+Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
+Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
+Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
+Bus 001 Device 002: ID 046d:0809 Logitech, Inc. Webcam Pro 9000
+Bus 003 Device 002: ID 046d:c016 Logitech, Inc. Optical Wheel Mouse
+</code>
+or this powerful tool, lsinput , 1st install it, and then try it, it lists all input devices including your USB device :
+<code>
+$ sudo apt-get install input-utils
+$ lsinput
+/dev/input/event0
+...
+/dev/input/event1
+...
+/dev/input/event2
+...
+/dev/input/event3
+bustype : BUS_USB
+vendor  : 0x46d
+product : 0xc016
+version : 272
+name    : "Logitech Optical USB Mouse"
+phys    : "usb-0000:00:1d.1-2/input0"
+uniq    : ""
+bits ev : EV_SYN EV_KEY EV_REL EV_MSC
+</code>
+udevadm , with this command line, you need to unplug the device before using the command and then plug it to see it:
+<code>
+$ udevadm monitor --udev
+monitor will print the received events for:
+UDEV - the event which udev sends out after rule processing
+UDEV  [1915.787445] add      /devices/pci0000:00/0000:00:1d.3/usb5/5-2 (usb)
+UDEV  [1915.796226] add      /devices/pci0000:00/0000:00:1d.3/usb5/5-2/5-2:1.0 (usb)
+</code>

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