Add `devm_dma_request_chan()` to simplify probe

Merge series from Bence Csókás <[e-mail]>:

The probe function of the atmel-quadspi driver got quite convoluted,
especially since the addition of SAMA7G5 support, that was forward-ported
from an older vendor kernel. To alleivate this - and similar problems in
the future - an effort was made to migrate as many functions as possible,
to their devm_ managed counterparts. Patch 1/2 adds the new
`devm_dma_request_chan()` function. Patch 2/2 then uses this APIs to
simplify the probe() function.

drivers/dma/dmaengine.c

···
 }
 EXPORT_SYMBOL_GPL(dma_release_channel);
 
+static void dmaenginem_release_channel(void *chan)
+{
+	dma_release_channel(chan);
+}
+
+/**
+ * devm_dma_request_chan - try to allocate an exclusive slave channel
+ * @dev:	pointer to client device structure
+ * @name:	slave channel name
+ *
+ * Returns pointer to appropriate DMA channel on success or an error pointer.
+ *
+ * The operation is managed and will be undone on driver detach.
+ */
+
+struct dma_chan *devm_dma_request_chan(struct device *dev, const char *name)
+{
+	struct dma_chan *chan = dma_request_chan(dev, name);
+	int ret = 0;
+
+	if (!IS_ERR(chan))
+		ret = devm_add_action_or_reset(dev, dmaenginem_release_channel, chan);
+
+	if (ret)
+		return ERR_PTR(ret);
+
+	return chan;
+}
+EXPORT_SYMBOL_GPL(devm_dma_request_chan);
+
 /**
  * dmaengine_get - register interest in dma_channels
  */

drivers/spi/atmel-quadspi.c

···
 	struct atmel_qspi *aq = spi_controller_get_devdata(ctrl);
 	int ret;
 
-	aq->rx_chan = dma_request_chan(&aq->pdev->dev, "rx");
+	aq->rx_chan = devm_dma_request_chan(&aq->pdev->dev, "rx");
 	if (IS_ERR(aq->rx_chan)) {
 		ret = dev_err_probe(&aq->pdev->dev, PTR_ERR(aq->rx_chan),
 				    "RX DMA channel is not available\n");
-		goto null_rx_chan;
+		aq->rx_chan = NULL;
+		return ret;
 	}
 
-	aq->tx_chan = dma_request_chan(&aq->pdev->dev, "tx");
+	aq->tx_chan = devm_dma_request_chan(&aq->pdev->dev, "tx");
 	if (IS_ERR(aq->tx_chan)) {
 		ret = dev_err_probe(&aq->pdev->dev, PTR_ERR(aq->tx_chan),
 				    "TX DMA channel is not available\n");
-		goto release_rx_chan;
+		aq->rx_chan = NULL;
+		aq->tx_chan = NULL;
+		return ret;
 	}
 
 	ctrl->dma_rx = aq->rx_chan;
···
 		 dma_chan_name(aq->tx_chan), dma_chan_name(aq->rx_chan));
 
 	return 0;
-
-release_rx_chan:
-	dma_release_channel(aq->rx_chan);
-	aq->tx_chan = NULL;
-null_rx_chan:
-	aq->rx_chan = NULL;
-	return ret;
-}
-
-static void atmel_qspi_dma_release(struct atmel_qspi *aq)
-{
-	if (aq->rx_chan)
-		dma_release_channel(aq->rx_chan);
-	if (aq->tx_chan)
-		dma_release_channel(aq->tx_chan);
 }
 
 static const struct atmel_qspi_ops atmel_qspi_ops = {
···
 
 	/* Request the IRQ */
 	irq = platform_get_irq(pdev, 0);
-	if (irq < 0) {
-		err = irq;
-		goto dma_release;
-	}
+	if (irq < 0)
+		return irq;
+
 	err = devm_request_irq(&pdev->dev, irq, atmel_qspi_interrupt,
 			       0, dev_name(&pdev->dev), aq);
 	if (err)
-		goto dma_release;
+		return err;
 
 	pm_runtime_set_autosuspend_delay(&pdev->dev, 500);
 	pm_runtime_use_autosuspend(&pdev->dev);
···
 
 	err = atmel_qspi_init(aq);
 	if (err)
-		goto dma_release;
+		return err;
 
 	err = spi_register_controller(ctrl);
 	if (err)
-		goto dma_release;
+		return err;
 
 	pm_runtime_mark_last_busy(&pdev->dev);
 	pm_runtime_put_autosuspend(&pdev->dev);
 
 	return 0;
-
-dma_release:
-	if (aq->caps->has_dma)
-		atmel_qspi_dma_release(aq);
-
-	return err;
 }
 
 static int atmel_qspi_sama7g5_suspend(struct atmel_qspi *aq)
···
 
 	ret = pm_runtime_get_sync(&pdev->dev);
 	if (ret >= 0) {
-		if (aq->caps->has_dma)
-			atmel_qspi_dma_release(aq);
-
 		if (aq->caps->has_gclk) {
 			ret = atmel_qspi_sama7g5_suspend(aq);
 			if (ret)

include/linux/dmaengine.h

···
 
 struct dma_chan *dma_request_chan(struct device *dev, const char *name);
 struct dma_chan *dma_request_chan_by_mask(const dma_cap_mask_t *mask);
+struct dma_chan *devm_dma_request_chan(struct device *dev, const char *name);
 
 void dma_release_channel(struct dma_chan *chan);
 int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps);
···
 {
 	return ERR_PTR(-ENODEV);
 }
+
+static inline struct dma_chan *devm_dma_request_chan(struct device *dev, const char *name)
+{
+	return ERR_PTR(-ENODEV);
+}
+
 static inline void dma_release_channel(struct dma_chan *chan)
 {
 }