Re: [PATCH v4 1/2] serial: Keep rs485 settings for devices without firmware node

[Lukas Wunner <lukas@wunner.de>]

On Thu, Oct 23, 2025 at 05:12:28PM +0200, Gerhard Engleder wrote:
> Commit fe7f0fa43cef ("serial: 8250: Support rs485 devicetree properties")
> retrieves rs485 properties for 8250 drivers. These properties are read
> from the firmware node of the device within uart_get_rs485_mode(). If the
> firmware node does not exist, then the rs485 flags are still reset. Thus,
> 8250 driver cannot set rs485 flags to enable a defined rs485 mode during
> driver loading. This is no problem so far, as no 8250 driver sets the
> rs485 flags.
> 
> The default rs485 mode can also be set by firmware nodes. But for some
> devices a firmware node does not exist. E.g., for a PCIe based serial
> interface on x86 no device tree is available and the ACPI information of
> the BIOS often cannot by modified. In this case it shall be possible,
> that a driver works out of the box by setting a reasonable default rs485
> mode.
> 
> If no firmware node exists, then it should be possible for the driver to
> set a reasonable default rs485 mode. Therefore, reset rs485 flags only
> if a firmware node exists.
> 
> Signed-off-by: Gerhard Engleder <eg@keba.com>

Reviewed-by: Lukas Wunner <lukas@wunner.de>