fix(rtc): fixed bbpll not calibrated from bootloader issue

components/esp_hw_support/port/esp32s3/rtc_clk.c

@@ -600,6 +600,25 @@ static bool rtc_clk_set_bbpll_always_on(void)
     return is_bbpll_on;
 }
 
+// Workaround for bootloader not calibrated well issue.
+// Placed in IRAM because disabling BBPLL may influence the cache
+void rtc_clk_recalib_bbpll(void)
+{
+    rtc_cpu_freq_config_t old_config;
+    rtc_clk_cpu_freq_get_config(&old_config);
+
+    // There are two paths we arrive here: 1. CPU reset. 2. Other reset reasons.
+    // - For other reasons, the bootloader will set CPU source to BBPLL and enable it. But there are calibration issues.
+    //   Turn off the BBPLL and do calibration again to fix the issue.
+    // - For CPU reset, the CPU source will be set to XTAL, while the BBPLL is kept to meet USB Serial JTAG's
+    //   requirements. In this case, we don't touch BBPLL to avoid USJ disconnection.
+    if (old_config.source == RTC_CPU_FREQ_SRC_PLL) {
+        rtc_clk_cpu_freq_set_xtal();
+        rtc_clk_cpu_freq_set_config(&old_config);
+    }
+}
+
+
 /* Name used in libphy.a:phy_chip_v7.o
  * TODO: update the library to use rtc_clk_xtal_freq_get
  */

components/esp_system/Kconfig

@@ -499,4 +499,13 @@ menu "ESP System Settings"
                 Using level 4 interrupt for Interrupt Watchdog and other system checks.
     endchoice
 
+    config ESP_SYSTEM_BBPLL_RECALIB
+        bool "Re-calibration BBPLL at startup"
+        depends on IDF_TARGET_ESP32S3
+        default y
+        help
+            This configuration helps to address an BBPLL inaccurate issue when boot from certain bootloader version,
+            which may increase about the boot-up time by about 200 us. Disable this when your bootloader is built with
+            ESP-IDF version v5.2 and above.
+
 endmenu  # ESP System Settings

components/esp_system/port/cpu_start.c

@@ -427,8 +427,16 @@ void IRAM_ATTR call_start_cpu0(void)
      * In this stage, we re-configure the Flash (and MSPI) to required configuration
      */
     spi_flash_init_chip_state();
+
+    // In earlier version of ESP-IDF, the PLL provided by bootloader is not stable enough.
+    // Do calibration again here so that we can use better clock for the timing tuning.
+#if CONFIG_ESP_SYSTEM_BBPLL_RECALIB
+    extern void rtc_clk_recalib_bbpll(void);
+    rtc_clk_recalib_bbpll();
+#endif
 #if CONFIG_IDF_TARGET_ESP32S3
-    //On other chips, this feature is not provided by HW, or hasn't been tested yet.
+    // This function needs to be called when PLL is enabled
+    // On other chips, this feature is not provided by HW, or hasn't been tested yet.
     spi_timing_flash_tuning();
 #endif