Man page 9 : snd_pcm_hw_rule_add

snd_pcm_hw_rule_add - add the hw-constraint rule

int snd_pcm_hw_rule_add(struct snd_pcm_runtime *  runtime , unsigned int  cond , int  var , snd_pcm_hw_rule_func_t  func , void *  private , int  dep , ... );

runtime
    the pcm runtime instance

cond
    condition bits

var
    the variable to evaluate

func
    the evaluation function

private
    the private data pointer passed to function

dep
    the dependent variables

...
    variable arguments

Zero if successful, or a negative error code on failure.