From 45c5fe475b281b80c426f2e9e80433dc5992a403 Mon Sep 17 00:00:00 2001
From: Suvesh Pratapa <66088488+suveshpratapa@users.noreply.github.com>
Date: Wed, 28 Aug 2024 14:38:31 -0400
Subject: [PATCH] [posix] add radio URL parameter `uart-init-deassert` to
 deassert DTR and RTS on init when flow control is disabled (#10644)

This lets us preserve legacy behavior where `uart-flow-control` was
not required even with hardware flow control enabled.
---
 src/posix/platform/hdlc_interface.cpp | 3 ++-
 src/posix/platform/radio_url.cpp      | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/posix/platform/hdlc_interface.cpp b/src/posix/platform/hdlc_interface.cpp
index 235af9ac8..321bfbae2 100644
--- a/src/posix/platform/hdlc_interface.cpp
+++ b/src/posix/platform/hdlc_interface.cpp
@@ -600,8 +600,9 @@ int HdlcInterface::OpenFile(const Url::Url &aRadioUrl)
         {
             tios.c_cflag |= CRTSCTS;
         }
-        else
+        else if (aRadioUrl.HasParam("uart-init-deassert"))
         {
+            // When flow control is disabled, deassert DTR and RTS on init
 #ifndef __APPLE__
             int flags;
 #endif
diff --git a/src/posix/platform/radio_url.cpp b/src/posix/platform/radio_url.cpp
index 57e1df0c2..c91baacba 100644
--- a/src/posix/platform/radio_url.cpp
+++ b/src/posix/platform/radio_url.cpp
@@ -84,6 +84,7 @@ const char *otSysGetRadioUrlHelpString(void)
     "    uart-stop[=number-of-bits]     Uart stop bit, default is 1.\n"                              \
     "    uart-baudrate[=baudrate]       Uart baud rate, default is 115200.\n"                        \
     "    uart-flow-control              Enable flow control, disabled by default.\n"                 \
+    "    uart-init-deassert             Deassert lines on init when flow control is disabled.\n"     \
     "    uart-reset                     Reset connection after hard resetting RCP(USB CDC ACM).\n"   \
     "\n"
 #else