For some years and since many kernel versions there are reports that RX UART DMA channel stops working at one point. So far the usual workaround was to disable RX DMA. This patches try to fix the underlying problem. When a running sdma script does not find any usable destination buffer to put its data into it just leads to stopping the channel being scheduled again. As solution we we manually retrigger the sdma script for this channel and by this dissolve the freeze. While this seems to work fine so far a further patch in this series increases the number of RX DMA periods for UART to reduce use cases running into such a situation. This patch series was tested with the current kernel and backported to kernel 4.15 with a special use case using a WL1837MOD via UART and provoking the hanging of UART RX DMA within seconds after starting a test application. It resulted in well known "Bluetooth: hci0: command 0x0408 tx timeout" errors and complete stop of UART data reception. Our Bluetooth traffic consists of many independent small packets, mostly only a few bytes, causing high usage of periods. Philipp Puschmann (4): dmaengine: imx-sdma: fix buffer ownership dmaengine: imx-sdma: fix dma freezes serial: imx: adapt rx buffer and dma periods dmaengine: imx-sdma: drop redundant variable drivers/dma/imx-sdma.c | 32 ++++++++++++++++++++++---------- drivers/tty/serial/imx.c | 5 ++--- 2 files changed, 24 insertions(+), 13 deletions(-) -- 2.23.0
