DMA Channel Priority of SPI and UART on iMX7

The driver of spi and uart on iMX7 use DMA for data transfer as configured by device tree. The SDMA of iMX7 assigns priority level(1~7) to each DMA channel. The SDMA driver sets default priority to 1. In uart and spi drivers, I don’t find any priority setting.
Because one customer finds uart7(2M baud rate) data transmission will suspend for seconds when there is heavy load on ecspi3(8Mbps). Could it be related to DMA channel priority ?

I find the setting in device tree, it is [dmas = <&sdma 4 7 1>][1]. There are 3 numbers for dmas. The first one is dma request, the second one is peripheral type, the third one is priority. The less the number is the higher the priority is, see here
UART7 transfer pending issue is much more related to multi-pthread application itself. As raw spi and uart transfer test doesn’t reproduce this issue. Just CPU load is very high, almost 100%.