[alsa-devel] [PATCH v2] pcm: null: Do not allow a period size of 0

[twischer at de.adit-jv.com]

From: Timo Wischer <twischer at de.adit-jv.com>

Some applications do not expect that get_period_size_min() could
return 0. Therefore these applications cannot use the null plugin without
this patch.
Due to there is no use case for having a period size of 0 this patch
disallows a period size of 0 when using the null plugin.

Signed-off-by: Timo Wischer <twischer at de.adit-jv.com>
---

Hi Takashi,

> Why 32?
I thought there is also no use case for a period of 1 frame. Therefore I
increased it to a 2^n value to also lower the CPU usage in case of null
plugin.

> Or does it cause a problem?
I do not see any issues here. But for example portaudio will automatically
choose a period size of 1 frame which will result in a higher CPU load.

But anyway I would also be fine with this higher CPU load if you prefer
this patch.

Best regards

Timo

 src/pcm/pcm_null.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/pcm/pcm_null.c b/src/pcm/pcm_null.c
index ff61624..1d81548 100644
--- a/src/pcm/pcm_null.c
+++ b/src/pcm/pcm_null.c
@@ -261,7 +261,17 @@ static snd_pcm_sframes_t snd_pcm_null_mmap_commit(snd_pcm_t *pcm,
 
 static int snd_pcm_null_hw_refine(snd_pcm_t *pcm ATTRIBUTE_UNUSED, snd_pcm_hw_params_t *params)
 {
-	int err = snd_pcm_hw_refine_soft(pcm, params);
+	int err;
+
+	/* Do not return a period size of 0 because for example portaudio cannot
+	 * handle it.
+	 */
+	err = _snd_pcm_hw_param_set_min(params, SND_PCM_HW_PARAM_PERIOD_SIZE, 1,
+					0);
+	if (err < 0)
+		return err;
+
+	err = snd_pcm_hw_refine_soft(pcm, params);
 	params->info = SND_PCM_INFO_MMAP | SND_PCM_INFO_MMAP_VALID |
 		       SND_PCM_INFO_RESUME | SND_PCM_INFO_PAUSE;
 	params->fifo_size = 0;
-- 
2.7.4