1 files changed, 84 insertions, 0 deletions
diff --git a/debian/patches-rt/0006-printk-nbcon-Add-callbacks-to-synchronize-with-drive.patch b/debian/patches-rt/0006-printk-nbcon-Add-callbacks-to-synchronize-with-drive.patch
new file mode 100644
index 0000000000..0323d580c4
--- /dev/null
+++ b/debian/patches-rt/0006-printk-nbcon-Add-callbacks-to-synchronize-with-drive.patch
@@ -0,0 +1,84 @@
+From: John Ogness <john.ogness@linutronix.de>
+Date: Mon, 18 Mar 2024 10:11:56 +0000
+Subject: [PATCH 06/46] printk: nbcon: Add callbacks to synchronize with driver
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.9/older/patches-6.9-rt5.tar.xz
+
+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. To provide the
+necessary synchronization, usually some driver-specific locking
+mechanism is used (for example, the port spinlock for uart
+serial consoles).
+
+Until now, usage of this driver-specific locking has been hidden
+from the printk-subsystem and implemented within the various
+console callbacks. However, for nbcon consoles, it is necessary
+that the printk-subsystem uses the driver-specific locking so
+that nbcon console ownership can be acquired _after_ the
+driver-specific locking has succeeded. This allows for lock
+contention to exist on the more context-friendly driver-specific
+locking rather than nbcon console ownership (for non-emergency
+and non-panic cases).
+
+Require nbcon consoles to implement two new callbacks
+(device_lock(), device_unlock()) that will use whatever
+synchronization mechanism the driver is using for itself.
+
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ include/linux/console.h |   43 +++++++++++++++++++++++++++++++++++++++++++
+ 1 file changed, 43 insertions(+)
+
+--- a/include/linux/console.h
++++ b/include/linux/console.h
+@@ -372,6 +372,49 @@ 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).
++	 *
++	 * The callback is always called from task context. It may use any
++	 * synchronization method required by the driver.
++	 *
++	 * IMPORTANT: The callback MUST 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;