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-rw-r--r--debian/patches-rt/0005-printk-nbcon-Add-detailed-doc-for-write_atomic.patch72
1 files changed, 72 insertions, 0 deletions
diff --git a/debian/patches-rt/0005-printk-nbcon-Add-detailed-doc-for-write_atomic.patch b/debian/patches-rt/0005-printk-nbcon-Add-detailed-doc-for-write_atomic.patch
new file mode 100644
index 0000000000..7d6a606df3
--- /dev/null
+++ b/debian/patches-rt/0005-printk-nbcon-Add-detailed-doc-for-write_atomic.patch
@@ -0,0 +1,72 @@
+From: John Ogness <john.ogness@linutronix.de>
+Date: Wed, 7 Feb 2024 18:38:14 +0000
+Subject: [PATCH 05/46] printk: nbcon: Add detailed doc for write_atomic()
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.9/older/patches-6.9-rt5.tar.xz
+
+The write_atomic() callback has special requirements and is
+allowed to use special helper functions. Provide detailed
+documentation of the callback so that a developer has a
+chance of implementing it correctly.
+
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ include/linux/console.h | 33 +++++++++++++++++++++++++++++----
+ 1 file changed, 29 insertions(+), 4 deletions(-)
+
+--- 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.
++ *
++ * 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;