From cd55eb927ddba835775dd71f2da7e2cdb7b59ea7 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 9 Feb 2026 12:21:15 -0600
Subject: [PATCH] [modbus] Batch UART reads to reduce loop overhead (#13822)

---
 esphome/components/modbus/modbus.cpp | 29 ++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/esphome/components/modbus/modbus.cpp b/esphome/components/modbus/modbus.cpp
index 357cd48e11..c1f5635028 100644
--- a/esphome/components/modbus/modbus.cpp
+++ b/esphome/components/modbus/modbus.cpp
@@ -19,16 +19,25 @@ void Modbus::setup() {
 void Modbus::loop() {
   const uint32_t now = App.get_loop_component_start_time();
 
-  while (this->available()) {
-    uint8_t byte;
-    this->read_byte(&byte);
-    if (this->parse_modbus_byte_(byte)) {
-      this->last_modbus_byte_ = now;
-    } else {
-      size_t at = this->rx_buffer_.size();
-      if (at > 0) {
-        ESP_LOGV(TAG, "Clearing buffer of %d bytes - parse failed", at);
-        this->rx_buffer_.clear();
+  // Read all available bytes in batches to reduce UART call overhead.
+  int avail = this->available();
+  uint8_t buf[64];
+  while (avail > 0) {
+    size_t to_read = std::min(static_cast<size_t>(avail), sizeof(buf));
+    if (!this->read_array(buf, to_read)) {
+      break;
+    }
+    avail -= to_read;
+
+    for (size_t i = 0; i < to_read; i++) {
+      if (this->parse_modbus_byte_(buf[i])) {
+        this->last_modbus_byte_ = now;
+      } else {
+        size_t at = this->rx_buffer_.size();
+        if (at > 0) {
+          ESP_LOGV(TAG, "Clearing buffer of %d bytes - parse failed", at);
+          this->rx_buffer_.clear();
+        }
       }
     }
   }