docs:[STM32][drv_gpio] Add detailed Doxygen comments for GET_PIN macro

bsp/stm32/libraries/HAL_Drivers/drivers/drv_gpio.h

@@ -23,6 +23,57 @@ extern "C" {
 
 #define __STM32_PORT(port)  GPIO##port##_BASE
 
+/**
+ * @brief  Calculates the RT-Thread global pin number from an STM32-specific port and pin.
+ *
+ * @details
+ * This macro provides a vendor-specific way to map a human-readable GPIO port
+ * (e.g., 'A', 'B') and pin number (0-15) to a single integer value that RT-Thread's
+ * pin device driver uses to identify a pin globally.
+ *
+ * The calculation is based on the memory address offset of the target GPIO port's
+ * base register relative to GPIOA. It assumes a linear memory map for GPIO ports.
+ *
+ * It includes special compile-time handling for different STM32 series, such as the
+ * STM32MP1, which have a different GPIO memory layout (e.g., 4KB stride between
+ * port registers) and may include special ports like GPIOZ.
+ *
+ * @param[in]  PORTx The GPIO port letter (e.g., A, B, C, D). Pass the letter without
+ * quotes (e.g., A, not 'A').
+ * @param[in]  PIN   The pin number within the port (an integer from 0 to 15).
+ *
+ * @return
+ * An `rt_base_t` integer representing the unique pin index for use with RT-Thread
+ * pin device driver functions (e.g., rt_pin_mode(), rt_pin_write()).
+ *
+ * @note
+ * - **STM32 & RT-Thread Specific:** This macro is highly dependent on the STM32 HAL
+ *   and RT-Thread's pin numbering convention. It relies on underlying HAL macros like
+ *   `__STM32_PORT()` and base address definitions like `GPIOA_BASE`.
+ * - **Not Portable:** Do not use this macro in code intended to be portable across
+ *   different microcontroller vendors.
+ * - **Compile-Time Evaluation:** The macro is evaluated entirely at compile time. The
+ *   correct implementation for the target STM32 series is selected via preprocessor
+ *   directives (e.g., `SOC_SERIES_STM32MP1`).
+ * - **Argument Evaluation:** As this is a preprocessor macro, its arguments are
+ *   substituted directly. Avoid passing expressions with side effects (e.g., `i++`)
+ *   as arguments, as they may be evaluated multiple times.
+ *
+ * @see rt_pin_mode()
+ * @see rt_pin_write()
+ * @see rt_pin_read()
+ *
+ * @code
+ * // Usage Example 1: Configure pin PD11 as a push-pull output.
+ * rt_pin_mode(GET_PIN(D, 11), PIN_MODE_OUTPUT);
+ *
+ * // Usage Example 2: Write a high logic level to pin PA5.
+ * rt_pin_write(GET_PIN(A, 5), PIN_HIGH);
+ *
+ * // Usage Example 3: Read the logic level from pin PC13.
+ * int level = rt_pin_read(GET_PIN(C, 13));
+ * @endcode
+ */
 #if defined(SOC_SERIES_STM32MP1)
 #define GET_PIN(PORTx,PIN) (GPIO##PORTx == GPIOZ) ? (176 + PIN) : ((rt_base_t)((16 * ( ((rt_base_t)__STM32_PORT(PORTx) - (rt_base_t)GPIOA_BASE)/(0x1000UL) )) + PIN))
 #else