ATMEL_PDC_RPR
pointer_reg = ATMEL_PDC_RPR;
head = atmel_uart_readl(port, ATMEL_PDC_RPR) - pdc->dma_addr;
atmel_uart_writel(port, ATMEL_PDC_RPR, atmel_port->pdc_rx[0].dma_addr);
writel(runtime->dma_addr, chip->regs + ATMEL_PDC_RPR);
bytes = readl(chip->regs + ATMEL_PDC_RPR);
.xpr = ATMEL_PDC_RPR,