fix: power the X4 Pro panel off before every restart

CHANGELOG.md

@@ -57,6 +57,7 @@
 
 ### Fixed
 
+- On the X4 Pro, the e-ink panel is powered off before every restart (after an OTA or SD card update, or a silent restart when leaving Wi-Fi) instead of staying powered until the reset.
 - File Transfer choices no longer appear preselected when opened on a touch device.
 - On the X4 Pro and Sticky, the Home screen no longer stalls waiting for the SD card while the Library indexes in the background.
 - Small images that are scaled up, such as a short progressive JPEG, are now cached after the first draw instead of being decoded again on every screen refresh.

src/activities/ActivityManager.cpp

@@ -1351,6 +1351,10 @@ RenderLock::RenderLock(const Mode mode) {
 
 RenderLock::RenderLock([[maybe_unused]] Activity&, const Mode mode) : RenderLock(mode) {}
 
+RenderLock::RenderLock(const unsigned long timeoutMs) {
+  isLocked = xSemaphoreTake(activityManager.renderingMutex, pdMS_TO_TICKS(timeoutMs)) == pdTRUE;
+}
+
 RenderLock::~RenderLock() {
   if (isLocked) {
     xSemaphoreGive(activityManager.renderingMutex);
@@ -1373,3 +1377,7 @@ void RenderLock::unlock() {
  * @note Must not be called from ISR context — xSemaphoreGetMutexHolder is not ISR-safe.
  */
 bool RenderLock::peek() { return xSemaphoreGetMutexHolder(activityManager.renderingMutex) != nullptr; }
+
+bool RenderLock::heldByCaller() {
+  return xSemaphoreGetMutexHolder(activityManager.renderingMutex) == xTaskGetCurrentTaskHandle();
+}

src/activities/RenderLock.h

@@ -10,10 +10,12 @@ class RenderLock {
   enum class Mode { Blocking, Try };
   explicit RenderLock(Mode mode = Mode::Blocking);
   explicit RenderLock(Activity&, Mode mode = Mode::Blocking);  // Compatibility overload used by activity call sites.
+  explicit RenderLock(unsigned long timeoutMs);                // bounded take; check ownsLock()
   RenderLock(const RenderLock&) = delete;
   RenderLock& operator=(const RenderLock&) = delete;
   ~RenderLock();
   void unlock();
   bool ownsLock() const { return isLocked; }
   static bool peek();
+  static bool heldByCaller();
 };

src/main.cpp

@@ -34,6 +34,7 @@
 #include "util/BootReason.h"
 
 #ifndef SIMULATOR
+#include <esp_system.h>
 #include <nvs.h>
 #endif
 
@@ -49,6 +50,7 @@
 #include "SilentRestart.h"
 #include "activities/Activity.h"
 #include "activities/ActivityManager.h"
+#include "activities/RenderLock.h"
 #include "activities/boot_sleep/ImageFolderIndex.h"
 #include "activities/home/BookActions.h"
 #include "activities/reader/KOReaderSyncActivity.h"
@@ -1101,6 +1103,28 @@ void enterDeepSleep(bool fromTimeout) {
   powerManager.startDeepSleep(gpio);
 }
 
+#if !defined(SIMULATOR) && FREEINK_DEVICE_X4PRO
+// Every esp_restart() (silent restart, OTA, SD update) runs this: the panel
+// stays powered between refreshes, so power it off (POF + deep sleep) instead
+// of leaving the booster on until the reset. begin() re-inits the controller
+// and the first paint after boot is non-differential, so lost RAM is harmless.
+// X4 Pro only: SDMMC keeps the SD card off the display's SPI bus, so the bus
+// lock cannot block here behind an SD transfer.
+static void powerOffPanelOnRestart() {
+  // ponytail: 3 s covers the longest refresh and stays under the 5 s task
+  // watchdog; a longer hold leaves the panel on.
+  constexpr unsigned long RENDER_LOCK_WAIT_MS = 3000;
+  const bool ownLock = RenderLock::heldByCaller();
+  RenderLock lock(ownLock ? 0UL : RENDER_LOCK_WAIT_MS);
+  if (!ownLock && !lock.ownsLock()) {
+    LOG_ERR("MAIN", "Render busy at restart; panel left powered");
+    return;
+  }
+  display.deepSleep();
+  LOG_INF("MAIN", "Panel powered off before restart");
+}
+#endif
+
 void setupDisplayAndFonts(const bool seamless, const bool loadReaderResources, const bool useReaderRenderStack) {
 #if !defined(SIMULATOR) && !FREEINK_MCU_C3
   // C3 X3/X4 detection already runs in HalGPIO::begin() before SPI owns the
@@ -1120,6 +1144,9 @@ void setupDisplayAndFonts(const bool seamless, const bool loadReaderResources, c
   display.begin();
 #else
   display.begin(seamless);
+#if FREEINK_DEVICE_X4PRO
+  esp_register_shutdown_handler(powerOffPanelOnRestart);
+#endif
 #endif
   renderer.begin();
   display.setInverted(SETTINGS.screenInverted != 0);