[PATCH v3 5/8] mtd: spi-nor: cadence-quadspi: Handle probe deferral while requesting DMA channel

[Vignesh Raghavendra <vigneshr@xxxxxx>]

dma_request_chan_by_mask() can throw EPROBE_DEFER if DMA provider
is not yet probed. Currently driver just falls back to using PIO mode
(which is less efficient) in this case. Instead return probe deferral
error as is so that driver will be re probed once DMA provider is
available.

Signed-off-by: Vignesh Raghavendra <vigneshr@xxxxxx>
---
 .../mtd/spi-nor/controllers/cadence-quadspi.c  | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/spi-nor/controllers/cadence-quadspi.c b/drivers/mtd/spi-nor/controllers/cadence-quadspi.c
index 608ca657ff7f..0570ebca135a 100644
--- a/drivers/mtd/spi-nor/controllers/cadence-quadspi.c
+++ b/drivers/mtd/spi-nor/controllers/cadence-quadspi.c
@@ -1169,7 +1169,7 @@ static void cqspi_controller_init(struct cqspi_st *cqspi)
 	cqspi_controller_enable(cqspi, 1);
 }
 
-static void cqspi_request_mmap_dma(struct cqspi_st *cqspi)
+static int cqspi_request_mmap_dma(struct cqspi_st *cqspi)
 {
 	dma_cap_mask_t mask;
 
@@ -1178,11 +1178,16 @@ static void cqspi_request_mmap_dma(struct cqspi_st *cqspi)
 
 	cqspi->rx_chan = dma_request_chan_by_mask(&mask);
 	if (IS_ERR(cqspi->rx_chan)) {
-		dev_err(&cqspi->pdev->dev, "No Rx DMA available\n");
+		int ret = PTR_ERR(cqspi->rx_chan);
+
+		if (ret != -EPROBE_DEFER)
+			dev_err(&cqspi->pdev->dev, "No Rx DMA available\n");
 		cqspi->rx_chan = NULL;
-		return;
+		return ret;
 	}
 	init_completion(&cqspi->rx_dma_complete);
+
+	return 0;
 }
 
 static const struct spi_nor_controller_ops cqspi_controller_ops = {
@@ -1269,8 +1274,11 @@ static int cqspi_setup_flash(struct cqspi_st *cqspi, struct device_node *np)
 			dev_dbg(nor->dev, "using direct mode for %s\n",
 				mtd->name);
 
-			if (!cqspi->rx_chan)
-				cqspi_request_mmap_dma(cqspi);
+			if (!cqspi->rx_chan) {
+				ret = cqspi_request_mmap_dma(cqspi);
+				if (ret == -EPROBE_DEFER)
+					goto err;
+			}
 		}
 	}
 
-- 
2.26.2