2 files changed, 45 insertions, 0 deletions

diff --git a/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl b/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl
index e13c4e67029f..df699e4323ef 100644
--- a/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl
+++ b/Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl
@@ -6173,6 +6173,47 @@ struct _snd_pcm_runtime {
          When no debug flag is set, this macro is ignored. 
       </para>
     </section>
+
+    <section id="useful-functions-snd-bug-on">
+      <title><function>snd_BUG_ON()</function></title>
+      <para>
+        <function>snd_BUG_ON()</function> macro is similar with
+        <function>WARN_ON()</function> macro. For example,  
+
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  snd_BUG_ON(!pointer);
+]]>
+          </programlisting>
+        </informalexample>
+
+        or it can be used as the condition,
+        <informalexample>
+          <programlisting>
+<![CDATA[
+  if (snd_BUG_ON(non_zero_is_bug))
+          return -EINVAL;
+]]>
+          </programlisting>
+        </informalexample>
+
+      </para>
+
+      <para>
+        The macro takes an conditional expression to evaluate.
+        When <constant>CONFIG_SND_DEBUG</constant>, is set, the
+        expression is actually evaluated. If it's non-zero, it shows
+        the warning message such as
+        <computeroutput>BUG? (xxx)</computeroutput>
+        normally followed by stack trace.  It returns the evaluated
+        value.
+        When no <constant>CONFIG_SND_DEBUG</constant> is set, this
+        macro always returns zero.
+      </para>
+
+    </section>
+
   </chapter>
 
 
diff --git a/include/sound/core.h b/include/sound/core.h
index 1a4ff0bdcf6a..938c36a0e874 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -28,6 +28,7 @@
 #include <linux/rwsem.h>                /* struct rw_semaphore */
 #include <linux/pm.h>                   /* pm_message_t */
 #include <linux/device.h>
+#include <linux/stringify.h>
 
 /* number of supported soundcards */
 #ifdef CONFIG_SND_DYNAMIC_MINORS
@@ -405,11 +406,14 @@ void snd_verbose_printd(const char *file, int line, const char *format, ...)
         dump_stack();                           \
 } while (0)
 
+#define snd_BUG_ON(cond)        WARN((cond), "BUG? (%s)\n", __stringify(cond))
+
 #else /* !CONFIG_SND_DEBUG */
 
 #define snd_printd(fmt, args...)        /* nothing */
 #define snd_assert(expr, args...)       (void)(expr)
 #define snd_BUG()                       /* nothing */
+#define snd_BUG_ON(cond)        ({/*(void)(cond);*/ 0;})  /* always false */
 
 #endif /* CONFIG_SND_DEBUG */