What does this implement/fix?

Reverts PR #14130 and PR #12519 which added gpio_reset_pin() and pin->setup() workarounds for default UART0 pins on ESP-IDF.

Background

Issue #10132 reported that LD2410 sensors stopped working on default UART0 pins. PR #12519 attributed the root cause to espressif/esp-idf#17459 (commit espressif/esp-idf@9ed617fb17 removing gpio_func_sel() from uart_set_pin()) and added gpio_reset_pin() calls as a workaround. However, gpio_reset_pin() disables the input buffer, which broke UART RX. PR #14130 then added pin->setup() to re-enable it — but that introduced a new regression (#14178) where gpio_config() removes the pullup set by gpio_reset_pin(), causing floating lines on RS-485/modbus devices.

Why the workaround was misattributed

The commit espressif/esp-idf@9ed617fb17 only removed gpio_func_sel() from the GPIO matrix fallback path — the code path for non-default pins. Default UART0 pins use the IOMUX path via uart_try_set_iomux_pin(), which returns false only when the pin doesn't match the default (upin->default_gpio != io_num). For default UART0 pins it returns true, so the GPIO matrix fallback block (where gpio_func_sel was removed) is never entered.

The IOMUX path has handled default UART0 pins correctly since uart_try_set_iomux_pin was introduced in 2021, including on ESP-IDF 5.4.2 where the issue was reported:

RX path: uart_set_pin() → uart_try_set_iomux_pin() → gpio_iomux_in() → gpio_ll_iomux_in() which calls PIN_INPUT_ENABLE() (re-enables input buffer)

TX path: uart_set_pin() → uart_try_set_iomux_pin() → gpio_iomux_out() → gpio_ll_iomux_out() which calls gpio_ll_func_sel() (sets IOMUX function)

Upstream ESP-IDF fix

The true root cause was an ESP-IDF bootloader bug: when the console was switched away from UART0 (e.g., to USB Serial JTAG or a different UART), the bootloader did not properly release the default UART0 TX pin. The TX output remained active, causing issues when user code later reconfigured those pins for a different UART purpose.

Espressif fixed this in bootloader_console.c by adding a release_default_console_io() function that:

1. Disables output on the UART0 TX pin (gpio_ll_output_disable())
2. Resets the pin to GPIO function (gpio_ll_func_sel(..., PIN_FUNC_GPIO))
3. Disconnects the UART RX signal (esp_rom_gpio_connect_in_signal(GPIO_MATRIX_CONST_ONE_INPUT, ...))

This fix closes both espressif/esp-idf#16764 and espressif/esp-idf#17459.

The fix is included in ESP-IDF v5.5.2+ (not in v5.5.1). ESPHome currently uses ESP-IDF v5.5.3, so the workarounds are no longer needed.

• v5.5 branch: fb20e147 (in v5.5.2+)
• v5.4 branch: aef9061d (not yet released, will be in v5.4.4)
• master: c4c932ad

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected) — policy
• Developer breaking change (an API change that could break external components) — policy
• Undocumented C++ API change (removal or change of undocumented public methods that lambda users may depend on) — policy
• Code quality improvements to existing code or addition of tests
• Other

Related issue or feature (if applicable):

• fixes Modbus CRC Check failed - with latest update. #14178

Pull request in esphome-docs with documentation (if applicable):

• N/A

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx
• LN882x
• nRF52840

Example entry for config.yaml:

# ESP32-C3 with PZEM-003 on default UART0 pins (no explicit pullup)
uart:
  tx_pin: GPIO21
  rx_pin: GPIO20
  baud_rate: 9600

modbus:

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.