Documentation/driver-api/console.rst

9 This type will be called 'system driver', and only one system driver is allowed
10 to exist. The system driver is persistent and it can never be unloaded, though
14 'modular driver' by this document. Multiple modular drivers can coexist at
15 any time with each driver sharing the console with other drivers including
16 the system driver. However, modular drivers cannot take over the console
17 that is currently occupied by another modular driver. (Exception: Drivers that
19 of driver occupying the consoles.) They can only take over the console that is
20 occupied by the system driver. In the same token, if the modular driver is
21 released by the console, the system driver will take over.
25 	 do_take_over_console() - load and bind driver to console layer
26 	 give_up_console() - unload driver; it will only work if driver
49      1. bind - this is a read/write file. It shows the status of the driver if
50         read, or acts to bind or unbind the driver to the virtual consoles
54 	  - means the driver is not bound and if echo'ed, commands the driver
58 	  - means the driver is bound and if echo'ed, commands the driver to
61      2. name - read-only file. Shows the name of the driver in this format::
66 	      '(S)' stands for a (S)ystem driver, i.e., it cannot be directly
69 	      'VGA+' is the name of the driver
74 	      In this case, '(M)' stands for a (M)odular driver, one that can be
79 When unbinding, the modular driver is detached first, and then the system
80 driver takes over the consoles vacated by the driver. Binding, on the other
81 hand, will bind the driver to the consoles that are currently occupied by a
82 system driver.
96 How useful is this feature? This is very useful for console driver
97 developers. By unbinding the driver from the console layer, one can unload the
98 driver, make changes, recompile, reload and rebind the driver without any need
112 give_up_console() is a wrapper to do_unregister_con_driver(), and a driver must
114 driver is bound or not.
116 Guidelines for console driver writers
123    or do_take_over_console(). do_register_con_driver() will just add the driver
132    driver, which was previously bound, becomes unbound.  The console layer
134    driver to check when it's legal to release these resources. Calling
138    rebind the driver to the console arrives.
140 4. Upon exit of the driver, ensure that the driver is totally unbound. If the
141    condition is satisfied, then the driver must call do_unregister_con_driver()
145    impossible for the driver to service console requests.  This can happen