esp_adc: make c2 atten0 calibration experimental

components/esp_adc/esp32c2/adc_cali_line_fitting.c

@@ -122,6 +122,9 @@ static esp_err_t check_valid(const adc_cali_line_fitting_config_t *config)
 {
     ESP_RETURN_ON_FALSE(config->unit_id < SOC_ADC_PERIPH_NUM, ESP_ERR_INVALID_ARG, TAG, "invalid ADC unit");
     ESP_RETURN_ON_FALSE((config->atten == ADC_ATTEN_DB_0 || config->atten == ADC_ATTEN_DB_11), ESP_ERR_NOT_SUPPORTED, TAG, "only ADC_ATTEN_DB_0 and ADC_ATTEN_DB_11 are supported");
+    if (config->atten == ADC_ATTEN_DB_0) {
+        ESP_LOGW(TAG, "Experimental: ADC Atten 0 calibration can now only used for inputs lower than 950mV. Calibration Scheme may get updated, DON'T USE FOR MASS PRODUCTION!");
+    }
 
     bool available_oneshot_bitwidth = (config->bitwidth >= SOC_ADC_RTC_MIN_BITWIDTH && config->bitwidth <= SOC_ADC_RTC_MAX_BITWIDTH);
     bool available_dma_bitwidth = (config->bitwidth >= SOC_ADC_DIGI_MIN_BITWIDTH && config->bitwidth <= SOC_ADC_DIGI_MAX_BITWIDTH);