staging: line6: avoid __sync_fetch_and_{and,or}

commit 9f613601 upstream.

__sync_fetch_and_and and __sync_fetch_and_or are functions that are provided
by gcc and depending on the target architecture may be implemented in libgcc,
which is not always available in the kernel. This leads to a build failure
on ARMv5:

drivers/built-in.o: In function `line6_pcm_release':
:(.text+0x3bfe80): undefined reference to `__sync_fetch_and_and_4'
drivers/built-in.o: In function `line6_pcm_acquire':
:(.text+0x3bff30): undefined reference to `__sync_fetch_and_or_4'

To work around this, we can use the kernel-provided cmpxchg macro.

Build-tested only.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Markus Grabner <grabner@icg.tugraz.at>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2:
 - Adjust context
 - Fix up two more instances of __sync_fetch_and_and() that were removed
   separately upstream]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/staging/line6/pcm.c

@@ -88,10 +88,13 @@ static DEVICE_ATTR(impulse_period, S_IWUSR | S_IRUGO, pcm_get_impulse_period,
 
 int line6_pcm_start(struct snd_line6_pcm *line6pcm, int channels)
 {
-	unsigned long flags_old =
-	    __sync_fetch_and_or(&line6pcm->flags, channels);
-	unsigned long flags_new = flags_old | channels;
-	int err = 0;
+	unsigned long flags_old, flags_new;
+	int err;
+
+	do {
+		flags_old = ACCESS_ONCE(line6pcm->flags);
+		flags_new = flags_old | channels;
+	} while (cmpxchg(&line6pcm->flags, flags_old, flags_new) != flags_old);
 
 #if LINE6_BACKUP_MONITOR_SIGNAL
 	if (!(line6pcm->line6->properties->capabilities & LINE6_BIT_HWMON)) {
@@ -133,10 +136,8 @@ int line6_pcm_start(struct snd_line6_pcm *line6pcm, int channels)
 		line6pcm->prev_fsize = 0;
 		err = line6_submit_audio_in_all_urbs(line6pcm);
 
-		if (err < 0) {
-			__sync_fetch_and_and(&line6pcm->flags, ~channels);
-			return err;
-		}
+		if (err < 0)
+			goto fail;
 	}
 
 	if (((flags_old & MASK_PLAYBACK) == 0) &&
@@ -160,20 +161,29 @@ int line6_pcm_start(struct snd_line6_pcm *line6pcm, int channels)
 		line6pcm->count_out = 0;
 		err = line6_submit_audio_out_all_urbs(line6pcm);
 
-		if (err < 0) {
-			__sync_fetch_and_and(&line6pcm->flags, ~channels);
-			return err;
-		}
+		if (err < 0)
+			goto fail;
 	}
 
 	return 0;
+
+fail:
+	do {
+		flags_old = ACCESS_ONCE(line6pcm->flags);
+		flags_new = flags_old & ~channels;
+	} while (cmpxchg(&line6pcm->flags, flags_old, flags_new) != flags_old);
+
+	return err;
 }
 
 int line6_pcm_stop(struct snd_line6_pcm *line6pcm, int channels)
 {
-	unsigned long flags_old =
-	    __sync_fetch_and_and(&line6pcm->flags, ~channels);
-	unsigned long flags_new = flags_old & ~channels;
+	unsigned long flags_old, flags_new;
+
+	do {
+		flags_old = ACCESS_ONCE(line6pcm->flags);
+		flags_new = flags_old & ~channels;
+	} while (cmpxchg(&line6pcm->flags, flags_old, flags_new) != flags_old);
 
 	if (((flags_old & MASK_CAPTURE) != 0) &&
 	    ((flags_new & MASK_CAPTURE) == 0)) {