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--- wiki2:linux_drivers [2019/09/22 07:53]
alfred [Helper functions]
+++ wiki2:linux_drivers [2020/09/11 20:57] (actual)
@@ Línea 100: / Línea 100: @@
 ===== 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 ====
@@ Línea 107: / Línea 117: @@
 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 134: / Línea 158: @@
 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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