spi: stm32-qspi: Use dma_request_chan() instead dma_request_slave_channel()

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

By using dma_request_chan() directly the driver can support deferred
probing against DMA.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20191212135550.4634-9-peter.ujfalusi@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-stm32-qspi.c

@@ -470,10 +470,11 @@ static int stm32_qspi_setup(struct spi_device *spi)
 	return 0;
 }
 
-static void stm32_qspi_dma_setup(struct stm32_qspi *qspi)
+static int stm32_qspi_dma_setup(struct stm32_qspi *qspi)
 {
 	struct dma_slave_config dma_cfg;
 	struct device *dev = qspi->dev;
+	int ret = 0;
 
 	memset(&dma_cfg, 0, sizeof(dma_cfg));
 
@@ -484,8 +485,13 @@ static void stm32_qspi_dma_setup(struct stm32_qspi *qspi)
 	dma_cfg.src_maxburst = 4;
 	dma_cfg.dst_maxburst = 4;
 
-	qspi->dma_chrx = dma_request_slave_channel(dev, "rx");
-	if (qspi->dma_chrx) {
+	qspi->dma_chrx = dma_request_chan(dev, "rx");
+	if (IS_ERR(qspi->dma_chrx)) {
+		ret = PTR_ERR(qspi->dma_chrx);
+		qspi->dma_chrx = NULL;
+		if (ret == -EPROBE_DEFER)
+			goto out;
+	} else {
 		if (dmaengine_slave_config(qspi->dma_chrx, &dma_cfg)) {
 			dev_err(dev, "dma rx config failed\n");
 			dma_release_channel(qspi->dma_chrx);
@@ -493,8 +499,11 @@ static void stm32_qspi_dma_setup(struct stm32_qspi *qspi)
 		}
 	}
 
-	qspi->dma_chtx = dma_request_slave_channel(dev, "tx");
-	if (qspi->dma_chtx) {
+	qspi->dma_chtx = dma_request_chan(dev, "tx");
+	if (IS_ERR(qspi->dma_chtx)) {
+		ret = PTR_ERR(qspi->dma_chtx);
+		qspi->dma_chtx = NULL;
+	} else {
 		if (dmaengine_slave_config(qspi->dma_chtx, &dma_cfg)) {
 			dev_err(dev, "dma tx config failed\n");
 			dma_release_channel(qspi->dma_chtx);
@@ -502,7 +511,13 @@ static void stm32_qspi_dma_setup(struct stm32_qspi *qspi)
 		}
 	}
 
+out:
 	init_completion(&qspi->dma_completion);
+
+	if (ret != -EPROBE_DEFER)
+		ret = 0;
+
+	return ret;
 }
 
 static void stm32_qspi_dma_free(struct stm32_qspi *qspi)
@@ -608,7 +623,10 @@ static int stm32_qspi_probe(struct platform_device *pdev)
 
 	qspi->dev = dev;
 	platform_set_drvdata(pdev, qspi);
-	stm32_qspi_dma_setup(qspi);
+	ret = stm32_qspi_dma_setup(qspi);
+	if (ret)
+		goto err;
+
 	mutex_init(&qspi->lock);
 
 	ctrl->mode_bits = SPI_RX_DUAL | SPI_RX_QUAD