diff options
| -rw-r--r-- | include/linux/console.h | 33 |
1 files changed, 29 insertions, 4 deletions
diff --git a/include/linux/console.h b/include/linux/console.h index 577b157fe4fb..35c64ee3827b 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -303,7 +303,7 @@ struct nbcon_write_context { /** * struct console - The console descriptor structure * @name: The name of the console driver - * @write: Write callback to output messages (Optional) + * @write: Legacy write callback to output messages (Optional) * @read: Read callback for console input (Optional) * @device: The underlying TTY device driver (Optional) * @unblank: Callback to unblank the console (Optional) @@ -320,7 +320,6 @@ struct nbcon_write_context { * @data: Driver private data * @node: hlist node for the console list * - * @write_atomic: Write callback for atomic context * @nbcon_state: State for nbcon consoles * @nbcon_seq: Sequence number of the next record for nbcon to print * @pbufs: Pointer to nbcon private buffer @@ -345,8 +344,34 @@ struct console { struct hlist_node node; /* nbcon console specific members */ - void (*write_atomic)(struct console *con, - struct nbcon_write_context *wctxt); + + /** + * @write_atomic: + * + * NBCON callback to write out text in any context. (Optional) + * + * This callback is called with the console already acquired. However, + * a higher priority context is allowed to take it over by default. + * + * The callback must call nbcon_enter_unsafe() and nbcon_exit_unsafe() + * around any code where the takeover is not safe, for example, when + * manipulating the serial port registers. + * + * nbcon_enter_unsafe() will fail if the context has lost the console + * ownership in the meantime. In this case, the callback is no longer + * allowed to go forward. It must back out immediately and carefully. + * The buffer content is also no longer trusted since it no longer + * belongs to the context. + * + * The callback should allow the takeover whenever it is safe. It + * increases the chance to see messages when the system is in trouble. + * + * The callback can be called from any context (including NMI). + * Therefore it must avoid usage of any locking and instead rely + * on the console ownership for synchronization. + */ + void (*write_atomic)(struct console *con, struct nbcon_write_context *wctxt); + atomic_t __private nbcon_state; atomic_long_t __private nbcon_seq; struct printk_buffers *pbufs; |