We use pulseaudio to play USB music，then there's a 100% probability of a broken tone, the kernel alway print follow logs:
[ 54.788437] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 54.788726] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 54.788975] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 54.789235] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 54.789495] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 55.121986] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 55.122718] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 55.124047] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 55.124736] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 55.125073] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
[ 55.125644] davinci-mcasp 48464000.mcasp: Transmit buffer underflow
the pulseaudi has use Edma(Linux), and Linux uses first 32 channels, BIOS uses last 32
&edma {
dma-requests = <32>;
};
