From 63db07a156756b30aa2fdc9b35e14f9d4c0ed16f Mon Sep 17 00:00:00 2001
From: tronikos <tronikos@users.noreply.github.com>
Date: Mon, 1 Apr 2024 13:21:53 -0700
Subject: [PATCH] Optimize QMC5883L: Read registers only for enabled sensors
 (#6458)

---
 esphome/components/qmc5883l/qmc5883l.cpp | 45 +++++++++++++++++-------
 1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/esphome/components/qmc5883l/qmc5883l.cpp b/esphome/components/qmc5883l/qmc5883l.cpp
index f03b6af191..4052b395f9 100644
--- a/esphome/components/qmc5883l/qmc5883l.cpp
+++ b/esphome/components/qmc5883l/qmc5883l.cpp
@@ -76,15 +76,8 @@ void QMC5883LComponent::dump_config() {
 float QMC5883LComponent::get_setup_priority() const { return setup_priority::DATA; }
 void QMC5883LComponent::update() {
   uint8_t status = false;
-  this->read_byte(QMC5883L_REGISTER_STATUS, &status);
-
-  uint16_t raw_x, raw_y, raw_z;
-  if (!this->read_byte_16_(QMC5883L_REGISTER_DATA_X_LSB, &raw_x) ||
-      !this->read_byte_16_(QMC5883L_REGISTER_DATA_Y_LSB, &raw_y) ||
-      !this->read_byte_16_(QMC5883L_REGISTER_DATA_Z_LSB, &raw_z)) {
-    this->status_set_warning();
-    return;
-  }
+  if (ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_DEBUG)
+    this->read_byte(QMC5883L_REGISTER_STATUS, &status);
 
   float mg_per_bit;
   switch (this->range_) {
@@ -99,11 +92,37 @@ void QMC5883LComponent::update() {
   }
 
   // in µT
-  const float x = int16_t(raw_x) * mg_per_bit * 0.1f;
-  const float y = int16_t(raw_y) * mg_per_bit * 0.1f;
-  const float z = int16_t(raw_z) * mg_per_bit * 0.1f;
+  float x = NAN, y = NAN, z = NAN;
+  if (this->x_sensor_ != nullptr || this->heading_sensor_ != nullptr) {
+    uint16_t raw_x;
+    if (!this->read_byte_16_(QMC5883L_REGISTER_DATA_X_LSB, &raw_x)) {
+      this->status_set_warning();
+      return;
+    }
+    x = int16_t(raw_x) * mg_per_bit * 0.1f;
+  }
+  if (this->y_sensor_ != nullptr || this->heading_sensor_ != nullptr) {
+    uint16_t raw_y;
+    if (!this->read_byte_16_(QMC5883L_REGISTER_DATA_Y_LSB, &raw_y)) {
+      this->status_set_warning();
+      return;
+    }
+    y = int16_t(raw_y) * mg_per_bit * 0.1f;
+  }
+  if (this->z_sensor_ != nullptr) {
+    uint16_t raw_z;
+    if (!this->read_byte_16_(QMC5883L_REGISTER_DATA_Z_LSB, &raw_z)) {
+      this->status_set_warning();
+      return;
+    }
+    z = int16_t(raw_z) * mg_per_bit * 0.1f;
+  }
+
+  float heading = NAN;
+  if (this->heading_sensor_ != nullptr) {
+    heading = atan2f(0.0f - x, y) * 180.0f / M_PI;
+  }
 
-  float heading = atan2f(0.0f - x, y) * 180.0f / M_PI;
   ESP_LOGD(TAG, "Got x=%0.02fµT y=%0.02fµT z=%0.02fµT heading=%0.01f° status=%u", x, y, z, heading, status);
 
   if (this->x_sensor_ != nullptr)