Following errors were seen in the past on imx6 when using serial:
[ 22.617622] imx-uart 2020000.serial: DMA transaction error.
[ 22.623228] imx-uart 2020000.serial: DMA transaction error.
[ 22.628826] imx-uart 2020000.serial: DMA transaction error.
[ 22.648951] imx-uart 2020000.serial: DMA transaction error.
[ 22.654558] imx-uart 2020000.serial: DMA transaction error.
[ 22.660156] imx-uart 2020000.serial: DMA transaction error.
Which is the reason why DMA for the serial ports
got disabled in commits:
efb362cd93 ("imx6: disable dma on uart")
3b4241071d ("imx6: disable UART dma")
As indicated on mailinglist discussion, the cause seems to be
the usage of very old SDMA firmware which is present in the soc:
[ 0.624302] imx-sdma 20ec000.sdma: Direct firmware load for imx/sdma/sdma-imx6q.bin failed with error -2
[ 0.624318] imx-sdma 20ec000.sdma: Falling back to user helper
[ 64.531607] imx-sdma 20ec000.sdma: external firmware not found, using ROM firmware
This patch adds the new firmware binary. (2196 bytes)
It is required to embed the binary into the kernel image, as it
gets loaded very early in the boot process where the rootfs is not
available yet:
[ 0.622966] imx-sdma 20ec000.sdma: loaded firmware 3.3
Extended testing shows that the DMA errors are not seen anymore
when using this newer firmware version.
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>
When this target got updated to 4.14, this patch got removed to
re-evaluate if it was still needed.
Extensive testing now shows this issue is still present.
Let's re-add the patch to fix it for now.
As the uart bus is very low bandwidth .. performance impact is negligible.
Boot log:
[ 22.513051] imx-uart 2020000.serial: DMA transaction error.
[ 22.522721] imx-uart 2020000.serial: DMA transaction error.
As a sidenote:
The patch mentiones an issue with RS485, but the bootlog
errors above were recorded with the uart ports in standard RS232 mode.
Compile/Run-tested on imx6/GW5200
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>
Koen Vandeputte