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 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 manually retrigger the sdma script for this channel and by this dissolve the freeze. While this seems to work fine so far, it may come to buffer overruns when the channel - even temporary - is stopped. This case has to be addressed by device drivers by increasing the number of DMA periods. 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. Signed-off-by: Philipp Puschmann <philipp.puschmann@xxxxxxxxx> Reviewed-by: Fugang Duan <fugang.duan@xxxxxxx> --- Changelog v5: - join with patch version from Jan Luebbe - adapt comments and patch descriptions - add Reviewed-by Changelog v4: - fixed the fixes tags Changelog v3: - fixes typo in dma_wmb - add fixes tags Changelog v2: - adapt title (this patches are not only for i.MX6) - improve some comments and patch descriptions - add a dma_wb() around BD_DONE flag - add Reviewed-by tags - split off "serial: imx: adapt rx buffer and dma periods" Philipp Puschmann (3): dmaengine: imx-sdma: fix buffer ownership dmaengine: imx-sdma: fix dma freezes dmaengine: imx-sdma: drop redundant variable drivers/dma/imx-sdma.c | 37 +++++++++++++++++++++++++++---------- 1 file changed, 27 insertions(+), 10 deletions(-) -- 2.23.0
