[RFC PATCH (alsa-lib)] pcm: Modify check condition in snd_pcm_sw_params_set_avail_min

[Koro Chen]

When we use a ping-ping buffer in capture, and if hw_ptr reported
at IRQ is a little smaller than period_size:

|xxxxxxxxxxxxxxxxxxxxxxxxxxxx--|-----------------------------|
                            hw_ptr < period_size

This available buffer will not be read since its size is smaller than
avail_min (which is set to be period_size), and read thread continues
to sleep. If the next hw_ptr is just a little larger than buffer_size,
overrun occurs.

This could be resolved by setting a small avail_min to kernel,
for example, 1, so read thread wakes up and reads every data at IRQ.
But current alsa-lib only allows avail_min to be at least period_size.
Remove the constraint and only check for zero case.

Signed-off-by: Koro Chen <koro.chen at mediatek.com>
---
 src/pcm/pcm.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
index f5fc728..8492689 100644
--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -5958,12 +5958,8 @@ int snd_pcm_sw_params_set_avail_min(snd_pcm_t *pcm, snd_pcm_sw_params_t *params,
 #endif
 {
 	assert(pcm && params);
-	/* Fix avail_min if it's below period size.  The period_size
-	 * defines the minimal wake-up timing accuracy, so it doesn't
-	 * make sense to set below that.
-	 */
-	if (val < pcm->period_size)
-		val = pcm->period_size;
+	if (!val)
+		val = 1;
 	params->avail_min = val;
 	return 0;
 }
-- 
1.7.9.5