• Wu Fengguang's avatar
    pulse-audio: fix bug on updating rpos · fd5723b3
    Wu Fengguang authored
    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: default avatarmalc <av1474@comtv.ru>
    Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
    fd5723b3
paaudio.c 11.5 KB