I'm using imx6ul-evk board (i.MX6UltraLite Evaluation Kit | NXP ) with linux 4.9.11. While communication between board and PC thrue uart with DMA I have a situation that board send to PC all it's Tx buffer - 4095 Bytes (if Tx frame more then 32 Bytes). When I'm turned off a DMA the communication without Tx 4095 Bytes, but board miss regular Tx frame ask. Figure below shows regular ask and regular answer (1 column its ask + answer not recognize on that scale). I found that software in the board send ask Tx frame, but uart driver ignore its and then software is fixed answer timeout (but PC even get not an ask). My qustchion is how can I fix DMA uart (in imx.c) and turn it on to solve problem with regular Tx frame?