linux-kernel - [PATCH] dt-bindings: serial: snps-dw-apb-uart: Add property to drain TX FIFO

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Date:   Mon, 16 Oct 2023 14:32:07 +1300
From:   Richard Laing <richard.laing@...iedtelesis.co.nz>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, ilpo.jarvinen@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        devicetree@...r.kernel.org,
        Richard Laing <richard.laing@...iedtelesis.co.nz>
Subject: [PATCH] dt-bindings: serial: snps-dw-apb-uart: Add property to drain TX FIFO

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@...iedtelesis.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