2 files changed, 21 insertions, 7 deletions

diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index 7fe0546c504a..6b6bef31e956 100644
--- a/Documentation/CodingStyle
+++ b/Documentation/CodingStyle
@@ -660,15 +660,23 @@ There are a number of driver model diagnostic macros in <linux/device.h>
 which you should use to make sure messages are matched to the right device
 and driver, and are tagged with the right level:  dev_err(), dev_warn(),
 dev_info(), and so forth.  For messages that aren't associated with a
-particular device, <linux/printk.h> defines pr_debug() and pr_info().
+particular device, <linux/printk.h> defines pr_notice(), pr_info(),
+pr_warn(), pr_err(), etc.
 
 Coming up with good debugging messages can be quite a challenge; and once
-you have them, they can be a huge help for remote troubleshooting.  Such
-messages should be compiled out when the DEBUG symbol is not defined (that
-is, by default they are not included).  When you use dev_dbg() or pr_debug(),
-that's automatic.  Many subsystems have Kconfig options to turn on -DDEBUG.
-A related convention uses VERBOSE_DEBUG to add dev_vdbg() messages to the
-ones already enabled by DEBUG.
+you have them, they can be a huge help for remote troubleshooting.  However
+debug message printing is handled differently than printing other non-debug
+messages.  While the other pr_XXX() functions print unconditionally,
+pr_debug() does not; it is compiled out by default, unless either DEBUG is
+defined or CONFIG_DYNAMIC_DEBUG is set.  That is true for dev_dbg() also,
+and a related convention uses VERBOSE_DEBUG to add dev_vdbg() messages to
+the ones already enabled by DEBUG.
+
+Many subsystems have Kconfig debug options to turn on -DDEBUG in the
+corresponding Makefile; in other cases specific files #define DEBUG.  And
+when a debug message should be unconditionally printed, such as if it is
+already inside a debug-related #ifdef secton, printk(KERN_DEBUG ...) can be
+used.
 
 
                 Chapter 14: Allocating memory
diff --git a/include/linux/printk.h b/include/linux/printk.h
index f086d6c99dbc..37f3a6589c1c 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -210,6 +210,12 @@ extern asmlinkage void dump_stack(void) __cold;
 #define pr_fmt(fmt) fmt
 #endif
 
+/*
+ * These can be used to print at the various log levels.
+ * All of these will print unconditionally, although note that pr_debug()
+ * and other debug macros are compiled out unless either DEBUG is defined
+ * or CONFIG_DYNAMIC_DEBUG is set.
+ */
 #define pr_emerg(fmt, ...) \
         printk(KERN_EMERG pr_fmt(fmt), ##__VA_ARGS__)
 #define pr_alert(fmt, ...) \