[PATCH v2 6/9] tty: serial: fsl-lpuart: Use cyclic DMA for Rx

The initial approach of DMA implementatin for RX is inefficient due to switching from PIO to DMA, this leads to overruns especially on instances with the smaller FIFO. To address these issues this patch uses a cyclic DMA for receiver path. Some part of the code is borrowed from atmel serial

[PATCH v2 6/9] tty: serial: fsl-lpuart: Use cyclic DMA for Rx

The initial approach of DMA implementatin for RX is inefficient due to switching from PIO to DMA, this leads to overruns especially on instances with the smaller FIFO. To address these issues this patch uses a cyclic DMA for receiver path. Some part of the code is borrowed from atmel serial