serial: stm32: move dma_request_chan() before clk_prepare_enable()

If dma_request_chan() returns a PROBE_DEFER error, clk_disable_unprepare()
will be called and USART clock will be disabled. But early console can be
still active on the same USART.

While moving dma_request_chan() before clk_prepare_enable(), the clock
won't be taken in case of a DMA PROBE_DEFER error, and so it doesn't need
to be disabled. Then USART is still clocked for early console.

Fixes: a7770a4b ("serial: stm32: defer probe for dma devices")
Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20221118170602.1057863-1-valentin.caron@foss.st.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -1680,22 +1680,10 @@ static int stm32_usart_serial_probe(struct platform_device *pdev)
 	if (!stm32port->info)
 		return -EINVAL;
 
-	ret = stm32_usart_init_port(stm32port, pdev);
-	if (ret)
-		return ret;
-
-	if (stm32port->wakeup_src) {
-		device_set_wakeup_capable(&pdev->dev, true);
-		ret = dev_pm_set_wake_irq(&pdev->dev, stm32port->port.irq);
-		if (ret)
-			goto err_deinit_port;
-	}
-
 	stm32port->rx_ch = dma_request_chan(&pdev->dev, "rx");
-	if (PTR_ERR(stm32port->rx_ch) == -EPROBE_DEFER) {
-		ret = -EPROBE_DEFER;
-		goto err_wakeirq;
-	}
+	if (PTR_ERR(stm32port->rx_ch) == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
+
 	/* Fall back in interrupt mode for any non-deferral error */
 	if (IS_ERR(stm32port->rx_ch))
 		stm32port->rx_ch = NULL;
@@ -1709,6 +1697,17 @@ static int stm32_usart_serial_probe(struct platform_device *pdev)
 	if (IS_ERR(stm32port->tx_ch))
 		stm32port->tx_ch = NULL;
 
+	ret = stm32_usart_init_port(stm32port, pdev);
+	if (ret)
+		goto err_dma_tx;
+
+	if (stm32port->wakeup_src) {
+		device_set_wakeup_capable(&pdev->dev, true);
+		ret = dev_pm_set_wake_irq(&pdev->dev, stm32port->port.irq);
+		if (ret)
+			goto err_deinit_port;
+	}
+
 	if (stm32port->rx_ch && stm32_usart_of_dma_rx_probe(stm32port, pdev)) {
 		/* Fall back in interrupt mode */
 		dma_release_channel(stm32port->rx_ch);
@@ -1745,19 +1744,11 @@ static int stm32_usart_serial_probe(struct platform_device *pdev)
 	pm_runtime_set_suspended(&pdev->dev);
 	pm_runtime_put_noidle(&pdev->dev);
 
-	if (stm32port->tx_ch) {
+	if (stm32port->tx_ch)
 		stm32_usart_of_dma_tx_remove(stm32port, pdev);
-		dma_release_channel(stm32port->tx_ch);
-	}
-
 	if (stm32port->rx_ch)
 		stm32_usart_of_dma_rx_remove(stm32port, pdev);
 
-err_dma_rx:
-	if (stm32port->rx_ch)
-		dma_release_channel(stm32port->rx_ch);
-
-err_wakeirq:
 	if (stm32port->wakeup_src)
 		dev_pm_clear_wake_irq(&pdev->dev);
 
@@ -1767,6 +1758,14 @@ static int stm32_usart_serial_probe(struct platform_device *pdev)
 
 	stm32_usart_deinit_port(stm32port);
 
+err_dma_tx:
+	if (stm32port->tx_ch)
+		dma_release_channel(stm32port->tx_ch);
+
+err_dma_rx:
+	if (stm32port->rx_ch)
+		dma_release_channel(stm32port->rx_ch);
+
 	return ret;
 }