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printk: nbcon: Add callbacks to synchronize with driver

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BugLink: https://bugs.launchpad.net/bugs/2060704

Console drivers typically must deal with access to the hardware
via user input/output (such as an interactive login shell) and
output of kernel messages via printk() calls.

Follow-up commits require that the printk subsystem is able to
synchronize with the driver. Require nbcon consoles to implement
two new callbacks (device_lock(), device_unlock()) that will
use whatever synchronization mechanism the driver is using for
itself (for example, the port lock for uart serial consoles).

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kevin Becker <kevin.becker@canonical.com>
This commit is contained in:
John Ogness
2024-03-18 10:11:56 +00:00
committed by Kevin Becker
parent d4aaab3e41
commit 3a5c4daac8
1 changed files with 42 additions and 0 deletions
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include/linux/console.h
+42
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@@ -352,6 +352,48 @@ struct console {
*/
void (*write_atomic)(struct console *con, struct nbcon_write_context *wctxt);
/**
* @device_lock:
*
* NBCON callback to begin synchronization with driver code.
*
* Console drivers typically must deal with access to the hardware
* via user input/output (such as an interactive login shell) and
* output of kernel messages via printk() calls. This callback is
* called by the printk-subsystem whenever it needs to synchronize
* with hardware access by the driver. It should be implemented to
* use whatever synchronization mechanism the driver is using for
* itself (for example, the port lock for uart serial consoles).
*
* This callback is always called from task context. It may use any
* synchronization method required by the driver. BUT this callback
* MUST also disable migration. The console driver may be using a
* synchronization mechanism that already takes care of this (such as
* spinlocks). Otherwise this function must explicitly call
* migrate_disable().
*
* The flags argument is provided as a convenience to the driver. It
* will be passed again to device_unlock(). It can be ignored if the
* driver does not need it.
*/
void (*device_lock)(struct console *con, unsigned long *flags);
/**
* @device_unlock:
*
* NBCON callback to finish synchronization with driver code.
*
* It is the counterpart to device_lock().
*
* This callback is always called from task context. It must
* appropriately re-enable migration (depending on how device_lock()
* disabled migration).
*
* The flags argument is the value of the same variable that was
* passed to device_lock().
*/
void (*device_unlock)(struct console *con, unsigned long flags);
atomic_t __private nbcon_state;
atomic_long_t __private nbcon_seq;
struct printk_buffers *pbufs;