Patchwork pulse-audio: fix bug on updating rpos

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Submitter Wu Fengguang
Date Sept. 29, 2010, 4:18 a.m.
Message ID <20100929041841.GA16868@localhost>
Download mbox | patch
Permalink /patch/66042/
State New
Headers show

Comments

Wu Fengguang - Sept. 29, 2010, 4:18 a.m.
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>
---
 audio/paaudio.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
malc - Sept. 29, 2010, 4:25 a.m.
On Wed, 29 Sep 2010, Wu Fengguang wrote:

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

[..snip..]

Thanks, applied.

Patch

--- qemu-kvm.orig/audio/paaudio.c	2010-09-29 10:28:25.000000000 +0800
+++ qemu-kvm/audio/paaudio.c	2010-09-29 12:11:45.000000000 +0800
@@ -111,8 +111,8 @@  static void *qpa_thread_out (void *arg)
             return NULL;
         }
 
+        pa->live = 0;
         pa->rpos = rpos;
-        pa->live -= decr;
         pa->decr += decr;
     }