[PATCH 2/2] serial: stm32: defer probe for dma devices

[Erwan Le Ray]

Defer device probe operation when a DMA channel request probe deferral.

With this change both DMA channels are acquired before DMA channels are
configured. Once no probe deferral is expected, DMAs are
configured and any failure in their configuration will make the driver
to fallback to interrupt mode as prior this change.

Signed-off-by: Erwan Le Ray <erwan.leray@xxxxxxxxxxx>
Signed-off-by: Etienne Carriere <etienne.carriere@xxxxxxxxxxx>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 2ac3b30477a7..7fa54ec11a84 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -1184,6 +1184,14 @@ static const struct of_device_id stm32_match[] = {
 MODULE_DEVICE_TABLE(of, stm32_match);
 #endif
 
+static void stm32_usart_of_dma_rx_remove(struct stm32_port *stm32port,
+					 struct platform_device *pdev)
+{
+	if (stm32port->rx_buf)
+		dma_free_coherent(&pdev->dev, RX_BUF_L, stm32port->rx_buf,
+				  stm32port->rx_dma_buf);
+}
+
 static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
 				       struct platform_device *pdev)
 {
@@ -1201,19 +1209,11 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
 	if (uart_console(port))
 		return -ENODEV;
 
-	/* Request DMA RX channel */
-	stm32port->rx_ch = dma_request_slave_channel(dev, "rx");
-	if (!stm32port->rx_ch) {
-		dev_info(dev, "rx dma alloc failed\n");
-		return -ENODEV;
-	}
 	stm32port->rx_buf = dma_alloc_coherent(&pdev->dev, RX_BUF_L,
 					       &stm32port->rx_dma_buf,
 					       GFP_KERNEL);
-	if (!stm32port->rx_buf) {
-		ret = -ENOMEM;
-		goto alloc_err;
-	}
+	if (!stm32port->rx_buf)
+		return -ENOMEM;
 
 	/* Configure DMA channel */
 	memset(&config, 0, sizeof(config));
@@ -1223,8 +1223,8 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
 	ret = dmaengine_slave_config(stm32port->rx_ch, &config);
 	if (ret < 0) {
 		dev_err(dev, "rx dma channel config failed\n");
-		ret = -ENODEV;
-		goto config_err;
+		stm32_usart_of_dma_rx_remove(stm32port, pdev);
+		return ret;
 	}
 
 	/* Prepare a DMA cyclic transaction */
@@ -1234,8 +1234,8 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
 					 DMA_PREP_INTERRUPT);
 	if (!desc) {
 		dev_err(dev, "rx dma prep cyclic failed\n");
-		ret = -ENODEV;
-		goto config_err;
+		stm32_usart_of_dma_rx_remove(stm32port, pdev);
+		return -ENODEV;
 	}
 
 	/* No callback as dma buffer is drained on usart interrupt */
@@ -1246,24 +1246,22 @@ static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
 	ret = dma_submit_error(dmaengine_submit(desc));
 	if (ret) {
 		dmaengine_terminate_sync(stm32port->rx_ch);
-		goto config_err;
+		stm32_usart_of_dma_rx_remove(stm32port, pdev);
+		return ret;
 	}
 
 	/* Issue pending DMA requests */
 	dma_async_issue_pending(stm32port->rx_ch);
 
 	return 0;
+}
 
-config_err:
-	dma_free_coherent(&pdev->dev,
-			  RX_BUF_L, stm32port->rx_buf,
-			  stm32port->rx_dma_buf);
-
-alloc_err:
-	dma_release_channel(stm32port->rx_ch);
-	stm32port->rx_ch = NULL;
-
-	return ret;
+static void stm32_usart_of_dma_tx_remove(struct stm32_port *stm32port,
+					 struct platform_device *pdev)
+{
+	if (stm32port->tx_buf)
+		dma_free_coherent(&pdev->dev, TX_BUF_L, stm32port->tx_buf,
+				  stm32port->tx_dma_buf);
 }
 
 static int stm32_usart_of_dma_tx_probe(struct stm32_port *stm32port,
@@ -1277,19 +1275,11 @@ static int stm32_usart_of_dma_tx_probe(struct stm32_port *stm32port,
 
 	stm32port->tx_dma_busy = false;
 
-	/* Request DMA TX channel */
-	stm32port->tx_ch = dma_request_slave_channel(dev, "tx");
-	if (!stm32port->tx_ch) {
-		dev_info(dev, "tx dma alloc failed\n");
-		return -ENODEV;
-	}
 	stm32port->tx_buf = dma_alloc_coherent(&pdev->dev, TX_BUF_L,
 					       &stm32port->tx_dma_buf,
 					       GFP_KERNEL);
-	if (!stm32port->tx_buf) {
-		ret = -ENOMEM;
-		goto alloc_err;
-	}
+	if (!stm32port->tx_buf)
+		return -ENOMEM;
 
 	/* Configure DMA channel */
 	memset(&config, 0, sizeof(config));
@@ -1299,22 +1289,11 @@ static int stm32_usart_of_dma_tx_probe(struct stm32_port *stm32port,
 	ret = dmaengine_slave_config(stm32port->tx_ch, &config);
 	if (ret < 0) {
 		dev_err(dev, "tx dma channel config failed\n");
-		ret = -ENODEV;
-		goto config_err;
+		stm32_usart_of_dma_tx_remove(stm32port, pdev);
+		return ret;
 	}
 
 	return 0;
-
-config_err:
-	dma_free_coherent(&pdev->dev,
-			  TX_BUF_L, stm32port->tx_buf,
-			  stm32port->tx_dma_buf);
-
-alloc_err:
-	dma_release_channel(stm32port->tx_ch);
-	stm32port->tx_ch = NULL;
-
-	return ret;
 }
 
 static int stm32_usart_serial_probe(struct platform_device *pdev)
@@ -1338,16 +1317,43 @@ static int stm32_usart_serial_probe(struct platform_device *pdev)
 		device_set_wakeup_capable(&pdev->dev, true);
 		ret = dev_pm_set_wake_irq(&pdev->dev, stm32port->port.irq);
 		if (ret)
-			goto err_nowup;
+			goto err_deinit_port;
 	}
 
-	ret = stm32_usart_of_dma_rx_probe(stm32port, pdev);
-	if (ret)
-		dev_info(&pdev->dev, "interrupt mode used for rx (no dma)\n");
+	stm32port->rx_ch = dma_request_chan(&pdev->dev, "rx");
+	if (PTR_ERR(stm32port->rx_ch) == -EPROBE_DEFER) {
+		ret = -EPROBE_DEFER;
+		goto err_wakeirq;
+	}
+	/* Fall back in interrupt mode for any non-deferral error */
+	if (IS_ERR(stm32port->rx_ch))
+		stm32port->rx_ch = NULL;
+
+	stm32port->tx_ch = dma_request_chan(&pdev->dev, "tx");
+	if (PTR_ERR(stm32port->tx_ch) == -EPROBE_DEFER) {
+		ret = -EPROBE_DEFER;
+		goto err_dma_rx;
+	}
+	/* Fall back in interrupt mode for any non-deferral error */
+	if (IS_ERR(stm32port->tx_ch))
+		stm32port->tx_ch = NULL;
 
-	ret = stm32_usart_of_dma_tx_probe(stm32port, pdev);
-	if (ret)
-		dev_info(&pdev->dev, "interrupt mode used for tx (no dma)\n");
+	if (stm32port->rx_ch && stm32_usart_of_dma_rx_probe(stm32port, pdev)) {
+		/* Fall back in interrupt mode */
+		dma_release_channel(stm32port->rx_ch);
+		stm32port->rx_ch = NULL;
+	}
+
+	if (stm32port->tx_ch && stm32_usart_of_dma_tx_probe(stm32port, pdev)) {
+		/* Fall back in interrupt mode */
+		dma_release_channel(stm32port->tx_ch);
+		stm32port->tx_ch = NULL;
+	}
+
+	if (!stm32port->rx_ch)
+		dev_info(&pdev->dev, "interrupt mode for rx (no dma)\n");
+	if (!stm32port->tx_ch)
+		dev_info(&pdev->dev, "interrupt mode for tx (no dma)\n");
 
 	platform_set_drvdata(pdev, &stm32port->port);
 
@@ -1368,30 +1374,23 @@ static int stm32_usart_serial_probe(struct platform_device *pdev)
 	pm_runtime_set_suspended(&pdev->dev);
 	pm_runtime_put_noidle(&pdev->dev);
 
-	if (stm32port->rx_ch) {
-		dmaengine_terminate_async(stm32port->rx_ch);
-		dma_release_channel(stm32port->rx_ch);
-	}
-
-	if (stm32port->rx_dma_buf)
-		dma_free_coherent(&pdev->dev,
-				  RX_BUF_L, stm32port->rx_buf,
-				  stm32port->rx_dma_buf);
-
 	if (stm32port->tx_ch) {
-		dmaengine_terminate_async(stm32port->tx_ch);
+		stm32_usart_of_dma_tx_remove(stm32port, pdev);
 		dma_release_channel(stm32port->tx_ch);
 	}
 
-	if (stm32port->tx_dma_buf)
-		dma_free_coherent(&pdev->dev,
-				  TX_BUF_L, stm32port->tx_buf,
-				  stm32port->tx_dma_buf);
+	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);
 
-err_nowup:
+err_deinit_port:
 	if (stm32port->wakeup_src)
 		device_set_wakeup_capable(&pdev->dev, false);
 
@@ -1418,28 +1417,20 @@ static int stm32_usart_serial_remove(struct platform_device *pdev)
 
 	stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAR);
 
+	if (stm32_port->tx_ch) {
+		dmaengine_terminate_async(stm32_port->tx_ch);
+		stm32_usart_of_dma_tx_remove(stm32_port, pdev);
+		dma_release_channel(stm32_port->tx_ch);
+	}
+
 	if (stm32_port->rx_ch) {
 		dmaengine_terminate_async(stm32_port->rx_ch);
+		stm32_usart_of_dma_rx_remove(stm32_port, pdev);
 		dma_release_channel(stm32_port->rx_ch);
 	}
 
-	if (stm32_port->rx_dma_buf)
-		dma_free_coherent(&pdev->dev,
-				  RX_BUF_L, stm32_port->rx_buf,
-				  stm32_port->rx_dma_buf);
-
 	stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
 
-	if (stm32_port->tx_ch) {
-		dmaengine_terminate_async(stm32_port->tx_ch);
-		dma_release_channel(stm32_port->tx_ch);
-	}
-
-	if (stm32_port->tx_dma_buf)
-		dma_free_coherent(&pdev->dev,
-				  TX_BUF_L, stm32_port->tx_buf,
-				  stm32_port->tx_dma_buf);
-
 	if (stm32_port->wakeup_src) {
 		dev_pm_clear_wake_irq(&pdev->dev);
 		device_init_wakeup(&pdev->dev, false);
-- 
2.17.1