CHAN_IDX
#define CHAN_BIT(chan) BIT(CHAN_IDX(chan))
#define CHAN_UPPER_BIT(chan) BIT(CHAN_IDX(chan) + 4)
#define CHAN_MASK(chan) (0x03U << (2 * CHAN_IDX(chan)))
#define CHAN_REG(base, chan) ((base) + (CHAN_IDX(chan) * 4))