pulse-audio: fix bug on updating rpos

Fix a rpos coordination bug between qpa_run_out() and qpa_thread_out(),
which shows up as playback noises.

	qpa_run_out()
			qpa_thread_out loop N critical section 1
	qpa_run_out()   qpa_thread_out loop N doing pa_simple_write()
	qpa_run_out()	qpa_thread_out loop N doing pa_simple_write()
			qpa_thread_out loop N critical section 2
			qpa_thread_out loop N+1 critical section 1
	qpa_run_out()	qpa_thread_out loop N+1 doing pa_simple_write()

In the above scheme, "qpa_thread_out loop N+1 critical section 1" will
get the same rpos as the one used by "qpa_thread_out loop N critical
section 1". So it will be reading dead samples from the old rpos.

The rpos can only be updated back to qpa_thread_out when there is a
qpa_run_out() run between two qpa_thread_out loops.

normal sequence:
	qpa_thread_out:
			hw->rpos (X0) => local rpos => pa->rpos (X1)
	qpa_run_out:
			pa->rpos (X1) => hw->rpos (X1)
	qpa_thread_out:
			hw->rpos (X1) => local rpos => pa->rpos (X2)

buggy sequence:
	qpa_thread_out:
			hw->rpos (X0) => local rpos => pa->rpos (X1)
	qpa_thread_out:
			hw->rpos (X0) => local rpos => pa->rpos (X1')

Obviously qpa_run_out() shall be called at least once between any two
qpa_thread_out loops (after pa->rpos is set), in order for the new
qpa_thread_out loop to see the updated rpos.

Setting pa->live to 0 does the trick. The next loop will have to wait
for one qpa_run_out() invocation in order to get a non-zero pa->live
and proceed.

Signed-off-by: malc <av1474@comtv.ru>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

diff --git a/audio/paaudio.c b/audio/paaudio.c
index 9118ece40cdbd2a7c259805f3650839a5c7a180d..ff71dac2a59a044cd4223f70421bfeedd3b16f48 100644 (file)
--- a/audio/paaudio.c
+++ b/audio/paaudio.c
@@ -110,8 +110,8 @@ static void *qpa_thread_out (void *arg)
             return NULL;
         }
 
+        pa->live = 0;
         pa->rpos = rpos;
-        pa->live -= decr;
         pa->decr += decr;
     }