DMA_DBTB
p->dbt[0] = readl_relaxed(p->base + DMA_DBTB);
p->dbt[1] = readl_relaxed(p->base + DMA_DBTB);
writel_relaxed(p->dbt[1], p->base + DMA_DBTB);
dbtx = DMA_DBTB;
'A' + (dbtx == DMA_DBTB), sg->len);
readl_relaxed(p->base + DMA_DBTB));