ALSA: pcm: Return negative delays from SNDRV_PCM_IOCTL_DELAY.

The commit c2c86a97175f ("ALSA: pcm: Remove set_fs() in PCM core code")
changed SNDRV_PCM_IOCTL_DELAY to return an inconsistent error instead of a
negative delay.  Originally the call would succeed and return the negative
delay.  The Chromium OS Audio Server (CRAS) gets confused and hangs when
the error is returned instead of the negative delay.

Help CRAS avoid the issue by rolling back the behavior to return a
negative delay instead of an error.

Fixes: c2c86a97175f ("ALSA: pcm: Remove set_fs() in PCM core code")
Signed-off-by: Jeffery Miller <jmiller@neverware.com>
Cc: <stable@vger.kernel.org> # v4.13+
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_compat.c

@@ -27,10 +27,11 @@ static int snd_pcm_ioctl_delay_compat(struct snd_pcm_substream *substream,
 				      s32 __user *src)
 {
 	snd_pcm_sframes_t delay;
+	int err;
 
-	delay = snd_pcm_delay(substream);
-	if (delay < 0)
-		return delay;
+	err = snd_pcm_delay(substream, &delay);
+	if (err)
+		return err;
 	if (put_user(delay, src))
 		return -EFAULT;
 	return 0;

sound/core/pcm_native.c

@@ -2692,7 +2692,8 @@ static int snd_pcm_hwsync(struct snd_pcm_substream *substream)
 	return err;
 }
 		
-static snd_pcm_sframes_t snd_pcm_delay(struct snd_pcm_substream *substream)
+static int snd_pcm_delay(struct snd_pcm_substream *substream,
+			 snd_pcm_sframes_t *delay)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	int err;
@@ -2708,7 +2709,9 @@ static snd_pcm_sframes_t snd_pcm_delay(struct snd_pcm_substream *substream)
 		n += runtime->delay;
 	}
 	snd_pcm_stream_unlock_irq(substream);
-	return err < 0 ? err : n;
+	if (!err)
+		*delay = n;
+	return err;
 }
 		
 static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
@@ -2916,11 +2919,13 @@ static int snd_pcm_common_ioctl(struct file *file,
 		return snd_pcm_hwsync(substream);
 	case SNDRV_PCM_IOCTL_DELAY:
 	{
-		snd_pcm_sframes_t delay = snd_pcm_delay(substream);
+		snd_pcm_sframes_t delay;
 		snd_pcm_sframes_t __user *res = arg;
+		int err;
 
-		if (delay < 0)
-			return delay;
+		err = snd_pcm_delay(substream, &delay);
+		if (err)
+			return err;
 		if (put_user(delay, res))
 			return -EFAULT;
 		return 0;
@@ -3008,13 +3013,7 @@ int snd_pcm_kernel_ioctl(struct snd_pcm_substream *substream,
 	case SNDRV_PCM_IOCTL_DROP:
 		return snd_pcm_drop(substream);
 	case SNDRV_PCM_IOCTL_DELAY:
-	{
-		result = snd_pcm_delay(substream);
-		if (result < 0)
-			return result;
-		*frames = result;
-		return 0;
-	}
+		return snd_pcm_delay(substream, frames);
 	default:
 		return -EINVAL;
 	}