GRCAN_MSG_SIZE
rd = grcan_ring_add(rd, GRCAN_MSG_SIZE, dma->rx.size);
slotindex = txwr / GRCAN_MSG_SIZE;
grcan_ring_add(txwr, GRCAN_MSG_SIZE, dma->tx.size));
u32 slots = txsize / GRCAN_MSG_SIZE - 1;
u32 used = grcan_ring_sub(txwr, eskbp, txsize) / GRCAN_MSG_SIZE;
i = priv->eskbp / GRCAN_MSG_SIZE;
priv->eskbp = grcan_ring_add(priv->eskbp, GRCAN_MSG_SIZE,
txrd = grcan_ring_add(txrd, GRCAN_MSG_SIZE, dma->tx.size);