TX_ASYNC
mcasp_set_bits(mcasp, DAVINCI_MCASP_ACLKXCTL_REG, TX_ASYNC);
mcasp_clr_bits(mcasp, DAVINCI_MCASP_ACLKXCTL_REG, TX_ASYNC);
mcasp_set_bits(mcasp, DAVINCI_MCASP_ACLKXCTL_REG, ACLKXE | TX_ASYNC);
return !(aclkxctl & TX_ASYNC);