ALSA: Introduce snd_BUG_ON() macro

Introduced snd_BUG_ON() macro as a replacement of snd_assert() macro.
snd_assert() is pretty ugly as it has the control flow in its argument.
OTOH, snd_BUG_ON() behaves like a normal conditional, thus it's much
easier to read the flow.

Signed-off-by: Takashi Iwai <[e-mail]>
Signed-off-by: Jaroslav Kysela <[e-mail]>

Documentation/sound/alsa/DocBook/writing-an-alsa-driver.tmpl

···
 	 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>
 
 

include/sound/core.h

···
 #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
···
 	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 */