linux - Hard time in understanding MODULE_DEVICE_TABLE(usb, id_table) usage

Question

I have a hard time understanding the exact usage of MODULE_DEVICE_TABLE(usb, id_table)

AFAIK this will generate the map files that will be used later by modprobe whenever a new device is inserted, it will match it against those map files and load the module if it matches.

But my misunderstanding is "isn't the module loaded anyway?"

I mean I already loaded it when I did insmod module-name. or am I missing something?

Answer 1

It is usually used to support hot-plugging, by loading/inserting the driver for a device if not already loaded.

There is a similar question here: Detect the presence of a device when it's hot plugged in Linux

(From my ans)

It works as follows:

1. Each driver in the code exposes its vendor/device id using:

     MODULE_DEVICE_TABLE(of, omap_mcspi_of_match);
   

2. At compilation time the build process extracts this infomation from all the drivers and prepares a device table.

3. When you insert the device, the device table is referred by the kernel and if an entry is found matching the device/vendor id of the added device, then its module is loaded and initialized.