Re: [PATCH 01/19] printk/nbcon: Use an enum to specify the required callback in console_is_usable()

The current usage of console_is_usable() is clumsy. The parameter
@use_atomic is boolean and thus not self-explanatory. The function is
called twice in situations when there are no-strict requirements.

Replace it with enum nbcon_write_cb which provides a more descriptive
values for all 3 situations: atomic, thread or any.

Note that console_is_usable() checks only NBCON_USE_ATOMIC because
.write_thread() callback is mandatory. But the other two values still
make sense because they describe the intention of the caller.

--- a/include/linux/console.h
+++ b/include/linux/console.h

@@ -202,6 +202,19 @@ enum cons_flags {
 	CON_NBCON_ATOMIC_UNSAFE	= BIT(9),
 };
 
+/**
+ * enum nbcon_write_cb - Defines which nbcon write() callback must be used based
+ *                       on the caller context.
+ * @NBCON_USE_ATOMIC: Use con->write_atomic().
+ * @NBCON_USE_THREAD: Use con->write_thread().
+ * @NBCON_USE_ANY:    The caller does not have any strict requirements.
+ */
+enum nbcon_write_cb {
+	NBCON_USE_ATOMIC,
+	NBCON_USE_THREAD,
+	NBCON_USE_ANY,

+};
+
 /**
  * struct nbcon_state - console state for nbcon consoles
  * @atom:	Compound of the state fields for atomic operations

@@ -622,7 +635,8 @@ extern void nbcon_kdb_release(struct nbcon_write_context *wctxt);
  * which can also play a role in deciding if @con can be used to print
  * records.
  */
-static inline bool console_is_usable(struct console *con, short flags, bool use_atomic)
+static inline bool console_is_usable(struct console *con, short flags,
+				     enum nbcon_write_cb nwc)
 {
 	if (!(flags & CON_ENABLED))
 		return false;

@@ -631,7 +645,7 @@ static inline bool console_is_usable(struct console *con, short flags, bool use_
 		return false;
 
 	if (flags & CON_NBCON) {
-		if (use_atomic) {
+		if (nwc & NBCON_USE_ATOMIC) {