linux-kernel - [PATCH v2 3/9] tty: serial: fsl_lpuart: handle EPROBE

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Date:   Fri, 21 Feb 2020 18:47:48 +0100
From:   Michael Walle <michael@...le.cc>
To:     linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Jiri Slaby <jslaby@...e.com>, Peng Fan <peng.fan@....com>,
        Vabhav Sharma <vabhav.sharma@....com>,
        Michael Walle <michael@...le.cc>
Subject: [PATCH v2 3/9] tty: serial: fsl_lpuart: handle EPROBE_DEFER for DMA

The DMA channel might not be available at the first probe time. This is
esp. the case if the DMA controller has an IOMMU mapping.

Use the new dma_request_chan() API and handle EPROBE_DEFER errors. Also
reorder the code a bit, so that we don't prepare the whole UART just to
determine that the DMA channel is not ready yet and we have to undo all
the stuff. Try to map the DMA channels earlier.

Signed-off-by: Michael Walle <michael@...le.cc>
---
 drivers/tty/serial/fsl_lpuart.c | 35 +++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index c31b8f3db6bf..fd9f60d0817a 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -2416,6 +2416,7 @@ static int lpuart_probe(struct platform_device *pdev)
 	const struct lpuart_soc_data *sdata = of_id->data;
 	struct device_node *np = pdev->dev.of_node;
 	struct lpuart_port *sport;
+	struct dma_chan *dma_chan;
 	struct resource *res;
 	int ret;
 
@@ -2483,6 +2484,26 @@ static int lpuart_probe(struct platform_device *pdev)
 	}
 	sport->port.line = ret;
 
+	dma_chan = dma_request_chan(sport->port.dev, "tx");
+	if (PTR_ERR(dma_chan) == -EPROBE_DEFER) {
+		ret = -EPROBE_DEFER;
+		goto failed_request_tx_dma;
+	} else if (IS_ERR(dma_chan))
+		dev_info(sport->port.dev, "DMA tx channel request failed, "
+				"operating without tx DMA\n");
+	else
+		sport->dma_tx_chan = dma_chan;
+
+	dma_chan = dma_request_chan(sport->port.dev, "rx");
+	if (PTR_ERR(dma_chan) == -EPROBE_DEFER) {
+		ret = -EPROBE_DEFER;
+		goto failed_request_rx_dma;
+	} else if (IS_ERR(dma_chan))
+		dev_info(sport->port.dev, "DMA rx channel request failed, "
+				"operating without rx DMA\n");
+	else
+		sport->dma_rx_chan = dma_chan;
+
 	ret = lpuart_enable_clks(sport);
 	if (ret)
 		goto failed_clock_enable;
@@ -2520,22 +2541,16 @@ static int lpuart_probe(struct platform_device *pdev)
 
 	sport->port.rs485_config(&sport->port, &sport->port.rs485);
 
-	sport->dma_tx_chan = dma_request_slave_channel(sport->port.dev, "tx");
-	if (!sport->dma_tx_chan)
-		dev_info(sport->port.dev, "DMA tx channel request failed, "
-				"operating without tx DMA\n");
-
-	sport->dma_rx_chan = dma_request_slave_channel(sport->port.dev, "rx");
-	if (!sport->dma_rx_chan)
-		dev_info(sport->port.dev, "DMA rx channel request failed, "
-				"operating without rx DMA\n");
-
 	return 0;
 
 failed_attach_port:
 failed_irq_request:
 	lpuart_disable_clks(sport);
 failed_clock_enable:
+	dma_release_channel(sport->dma_rx_chan);
+failed_request_rx_dma:
+	dma_release_channel(sport->dma_tx_chan);
+failed_request_tx_dma:
 failed_out_of_range:
 	if (sport->id_allocated)
 		ida_simple_remove(&fsl_lpuart_ida, sport->port.line);
-- 
2.20.1