Makes UART work at any APB Frequency (#8097)

Fixes HardwareSerial to work with IDF 5.1 on any CPU/APB Frequency (240MHz to 10MHZ), including user created low power modes.

Author: SuGlider

Diff for: cores/esp32/esp32-hal-uart.c

@@ -110,19 +110,6 @@ void uartDetachPins(uart_t* uart, int8_t rxPin, int8_t txPin, int8_t ctsPin, int
     UART_MUTEX_UNLOCK();  
 }
 
-// solves issue https://github.com/espressif/arduino-esp32/issues/6032
-// baudrate must be multiplied when CPU Frequency is lower than APB 80MHz
-uint32_t _get_effective_baudrate(uint32_t baudrate) 
-{
-    uint32_t Freq = getApbFrequency()/1000000;
-    if (Freq < 80) {
-        return 80 / Freq * baudrate;
-     }
-    else {
-        return baudrate;
-    }
-}
-
 // Routines that take care of UART events will be in the HardwareSerial Class code
 void uartGetEventQueue(uart_t* uart, QueueHandle_t *q)
 {
@@ -204,14 +191,8 @@ uart_t* uartBegin(uint8_t uart_nr, uint32_t baudrate, uint32_t config, int8_t rx
     uart_config.stop_bits = (config & 0x30) >> 4;
     uart_config.flow_ctrl = UART_HW_FLOWCTRL_DISABLE;
     uart_config.rx_flow_ctrl_thresh = rxfifo_full_thrhd;
-#if SOC_UART_SUPPORT_XTAL_CLK
-    // works independently of APB frequency
-    uart_config.source_clk = UART_SCLK_XTAL; // ESP32C3, ESP32S3
     uart_config.baud_rate = baudrate;
-#else
-    uart_config.source_clk = UART_SCLK_APB;  // ESP32, ESP32S2
-    uart_config.baud_rate = _get_effective_baudrate(baudrate);
-#endif
+    uart_config.source_clk = UART_SCLK_APB;
     ESP_ERROR_CHECK(uart_driver_install(uart_nr, rx_buffer_size, tx_buffer_size, 20, &(uart->uart_event_queue), 0));
     ESP_ERROR_CHECK(uart_param_config(uart_nr, &uart_config));
     ESP_ERROR_CHECK(uart_set_pin(uart_nr, txPin, rxPin, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE));
@@ -467,7 +448,7 @@ void uartSetBaudRate(uart_t* uart, uint32_t baud_rate)
     UART_MUTEX_LOCK();
     uint32_t sclk_freq;
     if(uart_get_sclk_freq(UART_SCLK_DEFAULT, &sclk_freq) == ESP_OK){
-        uart_ll_set_baudrate(UART_LL_GET_HW(uart->num), _get_effective_baudrate(baud_rate), sclk_freq);
+        uart_ll_set_baudrate(UART_LL_GET_HW(uart->num), baud_rate, sclk_freq);
     }
     UART_MUTEX_UNLOCK();
 }