From 1d91bf5759a615273348ed722aa3983488bce1c1 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 4 Sep 2025 11:02:17 -0500
Subject: [PATCH] [pcf8574] Add lazy input caching to reduce I2C bus usage

---
 esphome/components/pcf8574/pcf8574.cpp | 10 +++++++++-
 esphome/components/pcf8574/pcf8574.h   |  4 ++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/esphome/components/pcf8574/pcf8574.cpp b/esphome/components/pcf8574/pcf8574.cpp
index 848fbed484..5da6f92aae 100644
--- a/esphome/components/pcf8574/pcf8574.cpp
+++ b/esphome/components/pcf8574/pcf8574.cpp
@@ -16,6 +16,11 @@ void PCF8574Component::setup() {
   this->write_gpio_();
   this->read_gpio_();
 }
+void PCF8574Component::loop() {
+  // Invalidate the cache at the start of each loop.
+  // The actual read will happen on demand in digital_read()
+  this->cache_valid_ = false;
+}
 void PCF8574Component::dump_config() {
   ESP_LOGCONFIG(TAG, "PCF8574:");
   LOG_I2C_DEVICE(this)
@@ -25,7 +30,10 @@ void PCF8574Component::dump_config() {
   }
 }
 bool PCF8574Component::digital_read(uint8_t pin) {
-  this->read_gpio_();
+  // Read the inputs once per loop on demand and cache the result
+  if (!this->cache_valid_ && this->read_gpio_()) {
+    this->cache_valid_ = true;
+  }
   return this->input_mask_ & (1 << pin);
 }
 void PCF8574Component::digital_write(uint8_t pin, bool value) {
diff --git a/esphome/components/pcf8574/pcf8574.h b/esphome/components/pcf8574/pcf8574.h
index 6edc67fc96..fdeee1800d 100644
--- a/esphome/components/pcf8574/pcf8574.h
+++ b/esphome/components/pcf8574/pcf8574.h
@@ -15,6 +15,8 @@ class PCF8574Component : public Component, public i2c::I2CDevice {
 
   /// Check i2c availability and setup masks
   void setup() override;
+  /// Invalidate cache at start of each loop
+  void loop() override;
   /// Helper function to read the value of a pin.
   bool digital_read(uint8_t pin);
   /// Helper function to write the value of a pin.
@@ -37,6 +39,8 @@ class PCF8574Component : public Component, public i2c::I2CDevice {
   uint16_t output_mask_{0x00};
   /// The state read in read_gpio_ - 1 means HIGH, 0 means LOW
   uint16_t input_mask_{0x00};
+  /// Cache validity flag - true if we've read inputs this loop cycle
+  bool cache_valid_{false};
   bool pcf8575_;  ///< TRUE->16-channel PCF8575, FALSE->8-channel PCF8574
 };