Re: [PATCH v2 1/2] serial: Keep rs485 settings for devices without firmware node

[Lukas Wunner <lukas@wunner.de>]

On Sun, Oct 19, 2025 at 05:21:30PM +0200, Gerhard Engleder wrote:
> On 19.10.25 16:42, Lukas Wunner wrote:
> > BTW is there a good reason that you don't have a fwnode for your UART?
> > It seems odd to have a UART but not describe it in the devicetree.
> > Maybe that's the real problem and fixing it obviates the need for this
> > patch?
> 
> This auxiliary device is part of a FPGA based PCIe device. It is mostly
> used on x86 but arm64 is also possible in the future. There is no device
> tree or ACPI information available for this device. Think about an x86
> CPU module where you cannot influence the BIOS implementation and device
> tree is not available. IMO having a self describing PCIe device which
> works out of the box is best in this case.

In case you're not aware of it, it's possible to assign a software
fwnode to devices through device_add_software_node().  There is
precedent for its usage among 8250 drivers, see 8250_bcm2835aux.c
and 8250_exar.c.

So that would be an alternative to this patch.  Conceivably, your
FPGA might support different UART types and each might default to
different rs485 settings.  A software node as used by 8250_bcm2835aux.c
would allow you to define those settings through the driver_data.

Thanks,

Lukas