From bc8fa31a7605c729ac48fc40b0bc944deeef9867 Mon Sep 17 00:00:00 2001
From: puddly <32534428+puddly@users.noreply.github.com>
Date: Thu, 10 Sep 2026 20:32:31 +0000
Subject: [PATCH] [serial_proxy] Implement a no-op hardware flow control

---
 esphome/components/serial_proxy/serial_proxy.cpp | 9 +++------
 esphome/components/serial_proxy/serial_proxy.h   | 4 +---
 esphome/components/uart/uart_component.h         | 9 +++++++++
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/esphome/components/serial_proxy/serial_proxy.cpp b/esphome/components/serial_proxy/serial_proxy.cpp
index 61263287c4..cd9e1ae4b9 100644
--- a/esphome/components/serial_proxy/serial_proxy.cpp
+++ b/esphome/components/serial_proxy/serial_proxy.cpp
@@ -212,11 +212,6 @@ SerialProxyResult SerialProxy::configure(api::APIConnection *api_connection, uin
     ESP_LOGW(TAG, "Invalid parity: %u (must be 0-2)", parity);
     return SerialProxyResult::SERIAL_PROXY_RESULT_INVALID_ARGUMENT;
   }
-  if (flow_control) {
-    ESP_LOGW(TAG, "Hardware flow control requested but is not yet supported");
-    return SerialProxyResult::SERIAL_PROXY_RESULT_NOT_SUPPORTED;
-  }
-
   // Skip a no-op reconfigure. Clients routinely re-send identical settings on every
   // port open, and on a USB UART each apply is a CDC SET_LINE_CODING control transfer.
   // Some bridges watch line-coding changes as a signalling channel (a magic baud
@@ -227,7 +222,8 @@ SerialProxyResult SerialProxy::configure(api::APIConnection *api_connection, uin
       uart::UART_CONFIG_PARITY_ODD,
   };
   if (uart_comp->get_baud_rate() == baudrate && uart_comp->get_stop_bits() == stop_bits &&
-      uart_comp->get_data_bits() == data_size && uart_comp->get_parity() == PARITY_MAP[parity]) {
+      uart_comp->get_data_bits() == data_size && uart_comp->get_parity() == PARITY_MAP[parity] &&
+      uart_comp->get_flow_control() == flow_control) {
     ESP_LOGV(TAG, "Settings unchanged, skipping reconfigure [%" PRIu32 "]", this->instance_index_);
     return SerialProxyResult::SERIAL_PROXY_RESULT_OK;
   }
@@ -236,6 +232,7 @@ SerialProxyResult SerialProxy::configure(api::APIConnection *api_connection, uin
   uart_comp->set_baud_rate(baudrate);
   uart_comp->set_stop_bits(stop_bits);
   uart_comp->set_data_bits(data_size);
+  uart_comp->set_flow_control(flow_control);
 
   uart_comp->set_parity(PARITY_MAP[parity]);
 
diff --git a/esphome/components/serial_proxy/serial_proxy.h b/esphome/components/serial_proxy/serial_proxy.h
index 8ebb9ea94f..33b65c68b7 100644
--- a/esphome/components/serial_proxy/serial_proxy.h
+++ b/esphome/components/serial_proxy/serial_proxy.h
@@ -121,14 +121,13 @@ class SerialProxy final : public uart::UARTDevice, public Component {
 
   /// Get the port type
   api::enums::SerialProxyPortType get_port_type() const { return this->port_type_; }
-
   /// Handle a mode change requested by an API client
   SerialProxyResult set_mode_from_client(api::APIConnection *api_connection, api::enums::SerialProxyMode mode);
 
   /// Configure UART parameters and apply them
   /// @param api_connection The API connection requesting the change
   /// @param baudrate Baud rate in bits per second
-  /// @param flow_control True to enable hardware flow control
+  /// @param flow_control True to request hardware flow control
   /// @param parity Parity setting (0=none, 1=even, 2=odd)
   /// @param stop_bits Number of stop bits (1 or 2)
   /// @param data_size Number of data bits (5-8)
@@ -278,7 +277,6 @@ class SerialProxy final : public uart::UARTDevice, public Component {
   /// Current modem pin states
   bool rts_state_{false};
   bool dtr_state_{false};
-
 #ifdef USE_SERIAL_PROXY_TAP
   SerialProxyTap *tap_{nullptr};
 #endif
diff --git a/esphome/components/uart/uart_component.h b/esphome/components/uart/uart_component.h
index 3e52531791..01b17624b9 100644
--- a/esphome/components/uart/uart_component.h
+++ b/esphome/components/uart/uart_component.h
@@ -166,6 +166,14 @@ class UARTComponent {
   // @return Baud rate in bits per second.
   uint32_t get_baud_rate() const { return baud_rate_; }
 
+  // Requests hardware (RTS/CTS) flow control.
+  // @param flow_control True to request hardware flow control.
+  void set_flow_control(bool flow_control) { this->flow_control_ = flow_control; }
+
+  // Gets whether hardware flow control was requested.
+  // @return True when hardware flow control was requested.
+  bool get_flow_control() const { return this->flow_control_; }
+
 #if defined(USE_ESP8266) || defined(USE_ESP32)
   /**
    * Load the UART settings.
@@ -213,6 +221,7 @@ class UARTComponent {
   uint8_t stop_bits_{0};
   uint8_t data_bits_{0};
   UARTParityOptions parity_{UART_CONFIG_PARITY_NONE};
+  bool flow_control_{false};
 #ifdef USE_UART_DEBUGGER
   CallbackManager<void(UARTDirection, uint8_t)> debug_callback_{};
 #endif