[PATCH] ASoC: fsl: imx-pcm-fiq: omit fiq counter to avoid harm in unbalanced situations

[PATCH] ASoC: fsl: imx-pcm-fiq: omit fiq counter to avoid harm in unbalanced situations

[Oskar Schirmer]

Unbalanced calls to snd_imx_pcm_trigger() may result in endless
FIQ activity and thus provoke eternal sound. While on the first glance,
the switch statement looks pretty symmetric, the SUSPEND/RESUME
pair is not: the suspend case comes along snd_pcm_suspend_all(),
which for fsl/imx-pcm-fiq is called only at snd_soc_suspend(),
but the resume case originates straight from the SNDRV_PCM_IOCTL_RESUME.
This way userland may provoke an unbalanced resume, which might cause
the fiq_enable counter to increase and never return to zero again,
so eventually imx_pcm_fiq is never disabled.

Simply removing the fiq_enable will solve the problem, as long as
one never goes play and capture game simultaneously, but beware
trying both at once, the early TRIGGER_STOP will cut off the other
activity prematurely. So now playing and capturing is scrutinized
separately, instead of by counting.

Signed-off-by: Oskar Schirmer <oskar@scara.com>
---
 sound/soc/fsl/imx-pcm-fiq.c |   29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/sound/soc/fsl/imx-pcm-fiq.c b/sound/soc/fsl/imx-pcm-fiq.c
index 10e3305..f00b512 100644
--- a/sound/soc/fsl/imx-pcm-fiq.c
+++ b/sound/soc/fsl/imx-pcm-fiq.c
@@ -42,7 +42,8 @@ struct imx_pcm_runtime_data {
 	struct hrtimer hrt;
 	int poll_time_ns;
 	struct snd_pcm_substream *substream;
-	atomic_t running;
+	atomic_t playing;
+	atomic_t capturing;
 };
 
 static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
@@ -52,7 +53,7 @@ static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
 	struct snd_pcm_substream *substream = iprtd->substream;
 	struct pt_regs regs;
 
-	if (!atomic_read(&iprtd->running))
+	if (!atomic_read(&iprtd->playing) && !atomic_read(&iprtd->capturing))
 		return HRTIMER_NORESTART;
 
 	get_fiq_regs(&regs);
@@ -106,7 +107,6 @@ static int snd_imx_pcm_prepare(struct snd_pcm_substream *substream)
 	return 0;
 }
 
-static int fiq_enable;
 static int imx_pcm_fiq;
 
 static int snd_imx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
@@ -118,23 +118,27 @@ static int snd_imx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_RESUME:
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
-		atomic_set(&iprtd->running, 1);
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			atomic_set(&iprtd->playing, 1);
+		else
+			atomic_set(&iprtd->capturing, 1);
 		hrtimer_start(&iprtd->hrt, ns_to_ktime(iprtd->poll_time_ns),
 		      HRTIMER_MODE_REL);
-		if (++fiq_enable == 1)
-			enable_fiq(imx_pcm_fiq);
-
+		enable_fiq(imx_pcm_fiq);
 		break;
 
 	case SNDRV_PCM_TRIGGER_STOP:
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
-		atomic_set(&iprtd->running, 0);
-
-		if (--fiq_enable == 0)
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+			atomic_set(&iprtd->playing, 0);
+		else
+			atomic_set(&iprtd->capturing, 0);
+		if (!atomic_read(&iprtd->playing) &&
+				!atomic_read(&iprtd->capturing))
 			disable_fiq(imx_pcm_fiq);
-
 		break;
+
 	default:
 		return -EINVAL;
 	}
@@ -182,7 +186,8 @@ static int snd_imx_open(struct snd_pcm_substream *substream)
 
 	iprtd->substream = substream;
 
-	atomic_set(&iprtd->running, 0);
+	atomic_set(&iprtd->playing, 0);
+	atomic_set(&iprtd->capturing, 0);
 	hrtimer_init(&iprtd->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	iprtd->hrt.function = snd_hrtimer_callback;
 
-- 
1.7.9.5

Re: [PATCH] ASoC: fsl: imx-pcm-fiq: omit fiq counter to avoid harm in unbalanced situations

[Mark Brown]

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On Tue, Nov 12, 2013 at 03:46:38PM +0000, Oskar Schirmer wrote:
> Unbalanced calls to snd_imx_pcm_trigger() may result in endless
> FIQ activity and thus provoke eternal sound. While on the first glance,
> the switch statement looks pretty symmetric, the SUSPEND/RESUME

Applied, thanks.

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