An issue has been observed on the Broadcom BCM56160 serial port which
appears closely related to a similar issue on the Marvell Armada 38x
serial port.

Add a new property to force the TX FIFO to be drained before
changing the UART_LCR.

Signed-off-by: Richard Laing <richard.laing@alliedtelesis.co.nz>
---
 .../devicetree/bindings/serial/snps-dw-apb-uart.yaml        | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
index 17c553123f96..4266ef96832c 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml
@@ -114,6 +114,12 @@ properties:
       register. Define this if your serial port does not use this pin.
     type: boolean
 
+  drain-before-lcr-change:
+    description: Force TX buffer flush before LCR change. Make sure all
+    characters in the buffer are sent before reconfiguring. Define this if
+    the UART drops its FIFO when reconfiguring.
+    type: boolean
+
 required:
   - compatible
   - reg
-- 
2.42.0

On Mon, 16 Oct 2023 14:32:07 +1300, Richard Laing wrote:
> An issue has been observed on the Broadcom BCM56160 serial port which
> appears closely related to a similar issue on the Marvell Armada 38x
> serial port.
> 
> Add a new property to force the TX FIFO to be drained before
> changing the UART_LCR.
> 
> Signed-off-by: Richard Laing <richard.laing@alliedtelesis.co.nz>
> ---
>  .../devicetree/bindings/serial/snps-dw-apb-uart.yaml        | 6 ++++++
>  1 file changed, 6 insertions(+)
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:
./Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml:120:5: [error] syntax error: could not find expected ':' (syntax)

dtschema/dtc warnings/errors:
make[2]: *** Deleting file 'Documentation/devicetree/bindings/serial/snps-dw-apb-uart.example.dts'
Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml:120:5: could not find expected ':'
make[2]: *** [Documentation/devicetree/bindings/Makefile:26: Documentation/devicetree/bindings/serial/snps-dw-apb-uart.example.dts] Error 1
make[2]: *** Waiting for unfinished jobs....
./Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml:120:5: could not find expected ':'
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.yaml: ignoring, error parsing file
make[1]: *** [/builds/robherring/dt-review-ci/linux/Makefile:1427: dt_binding_check] Error 2
make: *** [Makefile:234: __sub-make] Error 2

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20231016013207.2249946-3-richard.laing@alliedtelesis.co.nz

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.