drivers: serial: stm32 databits depends on parity

On stm32, the M bits defines the length of the frame between the start
bit and the stop bit, eventually including the parity bit when enabled.
Fix configuration of databits to set correct M bits when parity is
enabled.
This commit tries to address issue zephyrproject-rtos#33351

Signed-off-by: Nicolas VINCENT <nicolas.vincent@vossloh.com>

drivers/serial/uart_stm32.c

@@ -227,39 +227,64 @@ static inline enum uart_config_stop_bits uart_stm32_ll2cfg_stopbits(uint32_t sb)
 	}
 }
 
-static inline uint32_t uart_stm32_cfg2ll_databits(enum uart_config_data_bits db)
+static inline uint32_t uart_stm32_cfg2ll_databits(enum uart_config_data_bits db,
+						  enum uart_config_parity p)
 {
 	switch (db) {
 /* Some MCU's don't support 7B or 9B datawidth */
 #ifdef LL_USART_DATAWIDTH_7B
 	case UART_CFG_DATA_BITS_7:
-		return LL_USART_DATAWIDTH_7B;
+		if (p == UART_CFG_PARITY_NONE) {
+			return LL_USART_DATAWIDTH_7B;
+		} else {
+			return LL_USART_DATAWIDTH_8B;
+		}
 #endif	/* LL_USART_DATAWIDTH_7B */
 #ifdef LL_USART_DATAWIDTH_9B
 	case UART_CFG_DATA_BITS_9:
 		return LL_USART_DATAWIDTH_9B;
 #endif	/* LL_USART_DATAWIDTH_9B */
 	case UART_CFG_DATA_BITS_8:
 	default:
+		if (p == UART_CFG_PARITY_NONE) {
+			return LL_USART_DATAWIDTH_8B;
+#ifdef LL_USART_DATAWIDTH_9B
+		} else {
+			return LL_USART_DATAWIDTH_9B;
+#endif
+		}
 		return LL_USART_DATAWIDTH_8B;
 	}
 }
 
-static inline enum uart_config_data_bits uart_stm32_ll2cfg_databits(uint32_t db)
+static inline enum uart_config_data_bits uart_stm32_ll2cfg_databits(uint32_t db,
+								    uint32_t p)
 {
 	switch (db) {
 /* Some MCU's don't support 7B or 9B datawidth */
 #ifdef LL_USART_DATAWIDTH_7B
 	case LL_USART_DATAWIDTH_7B:
-		return UART_CFG_DATA_BITS_7;
+		if (p == LL_USART_PARITY_NONE) {
+			return UART_CFG_DATA_BITS_7;
+		} else {
+			return UART_CFG_DATA_BITS_6;
+		}
 #endif	/* LL_USART_DATAWIDTH_7B */
 #ifdef LL_USART_DATAWIDTH_9B
 	case LL_USART_DATAWIDTH_9B:
-		return UART_CFG_DATA_BITS_9;
+		if (p == LL_USART_PARITY_NONE) {
+			return UART_CFG_DATA_BITS_9;
+		} else {
+			return UART_CFG_DATA_BITS_8;
+		}
 #endif	/* LL_USART_DATAWIDTH_9B */
 	case LL_USART_DATAWIDTH_8B:
 	default:
-		return UART_CFG_DATA_BITS_8;
+		if (p == LL_USART_PARITY_NONE) {
+			return UART_CFG_DATA_BITS_8;
+		} else {
+			return UART_CFG_DATA_BITS_7;
+		}
 	}
 }
 
@@ -302,7 +327,8 @@ static int uart_stm32_configure(const struct device *dev,
 	USART_TypeDef *UartInstance = UART_STRUCT(dev);
 	const uint32_t parity = uart_stm32_cfg2ll_parity(cfg->parity);
 	const uint32_t stopbits = uart_stm32_cfg2ll_stopbits(cfg->stop_bits);
-	const uint32_t databits = uart_stm32_cfg2ll_databits(cfg->data_bits);
+	const uint32_t databits = uart_stm32_cfg2ll_databits(cfg->data_bits,
+							     cfg->parity);
 	const uint32_t flowctrl = uart_stm32_cfg2ll_hwctrl(cfg->flow_ctrl);
 
 	/* Hardware doesn't support mark or space parity */
@@ -311,6 +337,12 @@ static int uart_stm32_configure(const struct device *dev,
 		return -ENOTSUP;
 	}
 
+	/* Driver does not supports parity + 9 databits */
+	if ((cfg->parity != UART_CFG_PARITY_NONE) &&
+	    (cfg->data_bits == UART_CFG_DATA_BITS_9)) {
+		return -ENOTSUP;
+	}
+
 #if defined(LL_USART_STOPBITS_0_5) && HAS_LPUART_1
 	if (IS_LPUART_INSTANCE(UartInstance) &&
 	    (cfg->stop_bits == UART_CFG_STOP_BITS_0_5)) {
@@ -388,7 +420,7 @@ static int uart_stm32_config_get(const struct device *dev,
 	cfg->stop_bits = uart_stm32_ll2cfg_stopbits(
 		uart_stm32_get_stopbits(dev));
 	cfg->data_bits = uart_stm32_ll2cfg_databits(
-		uart_stm32_get_databits(dev));
+		uart_stm32_get_databits(dev), uart_stm32_get_parity(dev));
 	cfg->flow_ctrl = uart_stm32_ll2cfg_hwctrl(
 		uart_stm32_get_hwctrl(dev));
 	return 0;