RE: [RFC][PATCH] serial: imx: Fix RS485 behaviour on disabled RX_DURING_TX

[Christoph Niedermaier <cniedermaier@dh-electronics.com>]

From: Tobias Jakobi (Compleo) <tobias.jakobi.compleo@gmail.com>
Sent: Thursday, March 7, 2024 12:07 PM
> 
> Hello,
> 
> I also noticed last year that RS485 was problematic on i.MX hardware. We
> use a i.MX7 SoC located on a SoM by manufacturer Toradex. The SoM itself
> is plugged into a proprietary board that features a Renesas ISL8xxx
> RS485 transceiver. We talk ModBus RTU over the RS485 link. The SoC is
> the ModBus master, the slave is a insulation monitoring device.
> 
> Since we source the i.MX through Toradex, I opened a thread on their
> community forum last year:
> https://community.toradex.com/t/fixing-native-rs485-de-toggling-on-uart6/20573
> 
> I also realized very quickly that the newly introduced loopback logic
> was the culprit. My solution currently consists of a new DT property
> that effectively disables the toggling of the loopback mode:
> https://gitlab.freedesktop.org/tobiasjakobi.compleo/linux-toradex/-
> /commit/98397c9436f48a149e2da0b2969a2d1d2d88c611
> 
> Anyway, I have tested Christoph's patch and can confirm that the patch
> (also) fixes the problems we are seeing. Test was done by applying the
> patch to 6.1.80. I haven't tested Rickard's patch so far.
> 
> Would be nice if this could later be backported to the 6.1.x kernel
> (this is the kernel we currently use on our hardware).

Rickard's patch in version 3 solved the same problem, so it should also
fix the problem on your side. It has already been accepted and is already
available in the next Kernel. It has a Fixes tag on it, so it should normally
be backported to the 6.1.x Kernel soon.

Regards
Christo1ph