AD_DMA_ADC
reg = ad1889_readw(chip, AD_DMA_ADC);
ad1889_writew(chip, AD_DMA_ADC, reg);
ad1889_readw(chip, AD_DMA_ADC);
ad1889_writew(chip, AD_DMA_ADC, AD_DMA_LOOP | AD_DMA_IM_CNT);