From b4c92dd8cbbf61810e876c3fbb3ca0ebaa199600 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 22 Dec 2025 14:29:47 -1000
Subject: [PATCH] [logger] Zephyr: Use k_str_out() with known length instead of
 printk() (#12619)

---
 esphome/components/logger/logger.h          |  4 ++--
 esphome/components/logger/logger_zephyr.cpp | 16 ++++++++--------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/esphome/components/logger/logger.h b/esphome/components/logger/logger.h
index 36195b919..2cedd7a76 100644
--- a/esphome/components/logger/logger.h
+++ b/esphome/components/logger/logger.h
@@ -118,11 +118,11 @@ static constexpr uint16_t MAX_HEADER_SIZE = 128;
 static constexpr size_t MAX_POINTER_REPRESENTATION = 2 + sizeof(void *) * 2 + 1;
 
 // Platform-specific: does write_msg_ add its own newline?
-// false: Caller must add newline to buffer before calling write_msg_ (ESP32, ESP8266, RP2040, LibreTiny)
+// false: Caller must add newline to buffer before calling write_msg_ (ESP32, ESP8266, RP2040, LibreTiny, Zephyr)
 //        Allows single write call with newline included for efficiency
 // true:  write_msg_ adds newline itself via puts()/println() (other platforms)
 //        Newline should NOT be added to buffer
-#if defined(USE_ESP32) || defined(USE_ESP8266) || defined(USE_RP2040) || defined(USE_LIBRETINY)
+#if defined(USE_ESP32) || defined(USE_ESP8266) || defined(USE_RP2040) || defined(USE_LIBRETINY) || defined(USE_ZEPHYR)
 static constexpr bool WRITE_MSG_ADDS_NEWLINE = false;
 #else
 static constexpr bool WRITE_MSG_ADDS_NEWLINE = true;
diff --git a/esphome/components/logger/logger_zephyr.cpp b/esphome/components/logger/logger_zephyr.cpp
index ec2ff3013..330dfa96e 100644
--- a/esphome/components/logger/logger_zephyr.cpp
+++ b/esphome/components/logger/logger_zephyr.cpp
@@ -6,6 +6,7 @@
 
 #include <zephyr/device.h>
 #include <zephyr/drivers/uart.h>
+#include <zephyr/sys/printk.h>
 #include <zephyr/usb/usb_device.h>
 
 namespace esphome::logger {
@@ -14,7 +15,7 @@ static const char *const TAG = "logger";
 
 #ifdef USE_LOGGER_USB_CDC
 void Logger::loop() {
-  if (this->uart_ != UART_SELECTION_USB_CDC || nullptr == this->uart_dev_) {
+  if (this->uart_ != UART_SELECTION_USB_CDC || this->uart_dev_ == nullptr) {
     return;
   }
   static bool opened = false;
@@ -62,18 +63,17 @@ void Logger::pre_setup() {
   ESP_LOGI(TAG, "Log initialized");
 }
 
-void HOT Logger::write_msg_(const char *msg, size_t) {
+void HOT Logger::write_msg_(const char *msg, size_t len) {
+  // Single write with newline already in buffer (added by caller)
 #ifdef CONFIG_PRINTK
-  printk("%s\n", msg);
+  k_str_out(const_cast<char *>(msg), len);
 #endif
-  if (nullptr == this->uart_dev_) {
+  if (this->uart_dev_ == nullptr) {
     return;
   }
-  while (*msg) {
-    uart_poll_out(this->uart_dev_, *msg);
-    ++msg;
+  for (size_t i = 0; i < len; ++i) {
+    uart_poll_out(this->uart_dev_, msg[i]);
   }
-  uart_poll_out(this->uart_dev_, '\n');
 }
 
 const LogString *Logger::get_uart_selection_() {