AD_DMA_DISR
st = ad1889_readl(chip, AD_DMA_DISR);
ad1889_writel(chip, AD_DMA_DISR, st);
ad1889_writel(chip, AD_DMA_DISR, AD_DMA_DISR_PTAI | AD_DMA_DISR_PMAI);
ad1889_readl(chip, AD_DMA_DISR); /* flush, dammit! */
ad1889_writel(chip, AD_DMA_DISR, AD_DMA_DISR_PMAE | AD_DMA_DISR_PTAE);