AW: [Customers.Eckelmann] [PATCH] serial: imx: disable DMA for RS-485 on i.MX6 SMP
From: Schenk, Gavin
Date: Fri Jun 23 2017 - 05:36:59 EST
> DMA support for half-duplex RS-485 never worked correctly on i.MX6Q/D
> due to an undiscovered SMP-related bug, instead of the real data being
> sent out, the rest of the transmit buffer is sent (xmit->tail jumps over
> xmit->head in imx_transmit_buffer and UART_XMIT_SIZE bytes are sent out)
> More details: https://lkml.org/lkml/2017/1/4/579
We see exactly this issue on our platform, based on i.MX6dl. We use the RS485 mode to implement a Modbus interface. We have another platform based on i.MX25 running the same Linux 4.9.30 code that is not affected!
> Disable it for that configuration until the bug is found and fixed.
> We need to know at probe time if we can enable DMA. (RS-485 could be
> enabled after that). Let's therefore only enable DMA if it is not an
> i.MX6Q/D UART with uart-has-rtscts in the DT and CONFIG_SMP enabled.
Uwe Kleine-KÃnig had the idea to disable DMA on the i.MX6dl based platform via dts and this is our current workaround.
Vorstand: Dipl.-Ing. Peter Frankenbach (Sprecher) Dipl.-Wi.-Ing. Philipp Eckelmann
Dr.-Ing. Marco MÃnchhof Dr.-Ing. Frank Uhlemann
Vorsitzender des Aufsichtsrats: Hubertus G. Krossa
Stv. Vorsitzender des Aufsichtsrats: Dr.-Ing. Gerd Eckelmann
Sitz der Gesellschaft: Berliner Str. 161, 65205 Wiesbaden, Amtsgericht Wiesbaden HRB 12636