--- /dev/null
+:orphan:
+
+===============
+Console Drivers
+===============
+
+The Linux kernel has 2 general types of console drivers. The first type is
+assigned by the kernel to all the virtual consoles during the boot process.
+This type will be called 'system driver', and only one system driver is allowed
+to exist. The system driver is persistent and it can never be unloaded, though
+it may become inactive.
+
+The second type has to be explicitly loaded and unloaded. This will be called
+'modular driver' by this document. Multiple modular drivers can coexist at
+any time with each driver sharing the console with other drivers including
+the system driver. However, modular drivers cannot take over the console
+that is currently occupied by another modular driver. (Exception: Drivers that
+call do_take_over_console() will succeed in the takeover regardless of the type
+of driver occupying the consoles.) They can only take over the console that is
+occupied by the system driver. In the same token, if the modular driver is
+released by the console, the system driver will take over.
+
+Modular drivers, from the programmer's point of view, have to call::
+
+ do_take_over_console() - load and bind driver to console layer
+ give_up_console() - unload driver; it will only work if driver
+ is fully unbound
+
+In newer kernels, the following are also available::
+
+ do_register_con_driver()
+ do_unregister_con_driver()
+
+If sysfs is enabled, the contents of /sys/class/vtconsole can be
+examined. This shows the console backends currently registered by the
+system which are named vtcon<n> where <n> is an integer from 0 to 15.
+Thus::
+
+ ls /sys/class/vtconsole
+ . .. vtcon0 vtcon1
+
+Each directory in /sys/class/vtconsole has 3 files::
+
+ ls /sys/class/vtconsole/vtcon0
+ . .. bind name uevent
+
+What do these files signify?
+
+ 1. bind - this is a read/write file. It shows the status of the driver if
+ read, or acts to bind or unbind the driver to the virtual consoles
+ when written to. The possible values are:
+
+ 0
+ - means the driver is not bound and if echo'ed, commands the driver
+ to unbind
+
+ 1
+ - means the driver is bound and if echo'ed, commands the driver to
+ bind
+
+ 2. name - read-only file. Shows the name of the driver in this format::
+
+ cat /sys/class/vtconsole/vtcon0/name
+ (S) VGA+
+
+ '(S)' stands for a (S)ystem driver, i.e., it cannot be directly
+ commanded to bind or unbind
+
+ 'VGA+' is the name of the driver
+
+ cat /sys/class/vtconsole/vtcon1/name
+ (M) frame buffer device
+
+ In this case, '(M)' stands for a (M)odular driver, one that can be
+ directly commanded to bind or unbind.
+
+ 3. uevent - ignore this file
+
+When unbinding, the modular driver is detached first, and then the system
+driver takes over the consoles vacated by the driver. Binding, on the other
+hand, will bind the driver to the consoles that are currently occupied by a
+system driver.
+
+NOTE1:
+ Binding and unbinding must be selected in Kconfig. It's under::
+
+ Device Drivers ->
+ Character devices ->
+ Support for binding and unbinding console drivers
+
+NOTE2:
+ If any of the virtual consoles are in KD_GRAPHICS mode, then binding or
+ unbinding will not succeed. An example of an application that sets the
+ console to KD_GRAPHICS is X.
+
+How useful is this feature? This is very useful for console driver
+developers. By unbinding the driver from the console layer, one can unload the
+driver, make changes, recompile, reload and rebind the driver without any need
+for rebooting the kernel. For regular users who may want to switch from
+framebuffer console to VGA console and vice versa, this feature also makes
+this possible. (NOTE NOTE NOTE: Please read fbcon.txt under Documentation/fb
+for more details.)
+
+Notes for developers
+====================
+
+do_take_over_console() is now broken up into::
+
+ do_register_con_driver()
+ do_bind_con_driver() - private function
+
+give_up_console() is a wrapper to do_unregister_con_driver(), and a driver must
+be fully unbound for this call to succeed. con_is_bound() will check if the
+driver is bound or not.
+
+Guidelines for console driver writers
+=====================================
+
+In order for binding to and unbinding from the console to properly work,
+console drivers must follow these guidelines:
+
+1. All drivers, except system drivers, must call either do_register_con_driver()
+ or do_take_over_console(). do_register_con_driver() will just add the driver
+ to the console's internal list. It won't take over the
+ console. do_take_over_console(), as it name implies, will also take over (or
+ bind to) the console.
+
+2. All resources allocated during con->con_init() must be released in
+ con->con_deinit().
+
+3. All resources allocated in con->con_startup() must be released when the
+ driver, which was previously bound, becomes unbound. The console layer
+ does not have a complementary call to con->con_startup() so it's up to the
+ driver to check when it's legal to release these resources. Calling
+ con_is_bound() in con->con_deinit() will help. If the call returned
+ false(), then it's safe to release the resources. This balance has to be
+ ensured because con->con_startup() can be called again when a request to
+ rebind the driver to the console arrives.
+
+4. Upon exit of the driver, ensure that the driver is totally unbound. If the
+ condition is satisfied, then the driver must call do_unregister_con_driver()
+ or give_up_console().
+
+5. do_unregister_con_driver() can also be called on conditions which make it
+ impossible for the driver to service console requests. This can happen
+ with the framebuffer console that suddenly lost all of its drivers.
+
+The current crop of console drivers should still work correctly, but binding
+and unbinding them may cause problems. With minimal fixes, these drivers can
+be made to work correctly.
+
+Antonino Daplas <adaplas@pol.net>
+++ /dev/null
-Console Drivers
-===============
-
-The Linux kernel has 2 general types of console drivers. The first type is
-assigned by the kernel to all the virtual consoles during the boot process.
-This type will be called 'system driver', and only one system driver is allowed
-to exist. The system driver is persistent and it can never be unloaded, though
-it may become inactive.
-
-The second type has to be explicitly loaded and unloaded. This will be called
-'modular driver' by this document. Multiple modular drivers can coexist at
-any time with each driver sharing the console with other drivers including
-the system driver. However, modular drivers cannot take over the console
-that is currently occupied by another modular driver. (Exception: Drivers that
-call do_take_over_console() will succeed in the takeover regardless of the type
-of driver occupying the consoles.) They can only take over the console that is
-occupied by the system driver. In the same token, if the modular driver is
-released by the console, the system driver will take over.
-
-Modular drivers, from the programmer's point of view, have to call:
-
- do_take_over_console() - load and bind driver to console layer
- give_up_console() - unload driver; it will only work if driver
- is fully unbound
-
-In newer kernels, the following are also available:
-
- do_register_con_driver()
- do_unregister_con_driver()
-
-If sysfs is enabled, the contents of /sys/class/vtconsole can be
-examined. This shows the console backends currently registered by the
-system which are named vtcon<n> where <n> is an integer from 0 to 15. Thus:
-
- ls /sys/class/vtconsole
- . .. vtcon0 vtcon1
-
-Each directory in /sys/class/vtconsole has 3 files:
-
- ls /sys/class/vtconsole/vtcon0
- . .. bind name uevent
-
-What do these files signify?
-
- 1. bind - this is a read/write file. It shows the status of the driver if
- read, or acts to bind or unbind the driver to the virtual consoles
- when written to. The possible values are:
-
- 0 - means the driver is not bound and if echo'ed, commands the driver
- to unbind
-
- 1 - means the driver is bound and if echo'ed, commands the driver to
- bind
-
- 2. name - read-only file. Shows the name of the driver in this format:
-
- cat /sys/class/vtconsole/vtcon0/name
- (S) VGA+
-
- '(S)' stands for a (S)ystem driver, i.e., it cannot be directly
- commanded to bind or unbind
-
- 'VGA+' is the name of the driver
-
- cat /sys/class/vtconsole/vtcon1/name
- (M) frame buffer device
-
- In this case, '(M)' stands for a (M)odular driver, one that can be
- directly commanded to bind or unbind.
-
- 3. uevent - ignore this file
-
-When unbinding, the modular driver is detached first, and then the system
-driver takes over the consoles vacated by the driver. Binding, on the other
-hand, will bind the driver to the consoles that are currently occupied by a
-system driver.
-
-NOTE1: Binding and unbinding must be selected in Kconfig. It's under:
-
-Device Drivers -> Character devices -> Support for binding and unbinding
-console drivers
-
-NOTE2: If any of the virtual consoles are in KD_GRAPHICS mode, then binding or
-unbinding will not succeed. An example of an application that sets the console
-to KD_GRAPHICS is X.
-
-How useful is this feature? This is very useful for console driver
-developers. By unbinding the driver from the console layer, one can unload the
-driver, make changes, recompile, reload and rebind the driver without any need
-for rebooting the kernel. For regular users who may want to switch from
-framebuffer console to VGA console and vice versa, this feature also makes
-this possible. (NOTE NOTE NOTE: Please read fbcon.txt under Documentation/fb
-for more details.)
-
-Notes for developers:
-=====================
-
-do_take_over_console() is now broken up into:
-
- do_register_con_driver()
- do_bind_con_driver() - private function
-
-give_up_console() is a wrapper to do_unregister_con_driver(), and a driver must
-be fully unbound for this call to succeed. con_is_bound() will check if the
-driver is bound or not.
-
-Guidelines for console driver writers:
-=====================================
-
-In order for binding to and unbinding from the console to properly work,
-console drivers must follow these guidelines:
-
-1. All drivers, except system drivers, must call either do_register_con_driver()
- or do_take_over_console(). do_register_con_driver() will just add the driver
- to the console's internal list. It won't take over the
- console. do_take_over_console(), as it name implies, will also take over (or
- bind to) the console.
-
-2. All resources allocated during con->con_init() must be released in
- con->con_deinit().
-
-3. All resources allocated in con->con_startup() must be released when the
- driver, which was previously bound, becomes unbound. The console layer
- does not have a complementary call to con->con_startup() so it's up to the
- driver to check when it's legal to release these resources. Calling
- con_is_bound() in con->con_deinit() will help. If the call returned
- false(), then it's safe to release the resources. This balance has to be
- ensured because con->con_startup() can be called again when a request to
- rebind the driver to the console arrives.
-
-4. Upon exit of the driver, ensure that the driver is totally unbound. If the
- condition is satisfied, then the driver must call do_unregister_con_driver()
- or give_up_console().
-
-5. do_unregister_con_driver() can also be called on conditions which make it
- impossible for the driver to service console requests. This can happen
- with the framebuffer console that suddenly lost all of its drivers.
-
-The current crop of console drivers should still work correctly, but binding
-and unbinding them may cause problems. With minimal fixes, these drivers can
-be made to work correctly.
-
-==========================
-Antonino Daplas <adaplas@pol.net>
-
Assuming the VGA driver can be unloaded, one must first unbind the VGA driver
from the console layer before unloading the driver. The VGA driver cannot be
unloaded if it is still bound to the console layer. (See
-Documentation/console/console.txt for more information).
+Documentation/console/console.rst for more information).
This is more complicated in the case of the framebuffer console (fbcon),
because fbcon is an intermediate layer between the console and the drivers::
fbcon.
So, how do we unbind fbcon from the console? Part of the answer is in
-Documentation/console/console.txt. To summarize:
+Documentation/console/console.rst. To summarize:
Echo a value to the bind file that represents the framebuffer console
driver. So assuming vtcon1 represents fbcon, then::
select the console driver that will serve as the backend for the
virtual terminals.
- See <file:Documentation/console/console.txt> for more
+ See <file:Documentation/console/console.rst> for more
information. For framebuffer console users, please refer to
<file:Documentation/fb/fbcon.rst>.
projects / openwrt / staging / blogic.git / commitdiff