RADEON_DAC2_DAC_CLK_SEL
dac2_cntl &= ~RADEON_DAC2_DAC_CLK_SEL;
dac2_cntl = RREG32(RADEON_DAC_CNTL2) & ~(RADEON_DAC2_DAC_CLK_SEL);
dac2_cntl = RREG32(RADEON_DAC_CNTL2) | RADEON_DAC2_DAC_CLK_SEL;