dmaengine: stm32-dma: driver defers probe for reset

Change STM32 DMA driver to defer its probe operation when reset
controller is expected but has not been probed yet when DMA
device is probed.

Changes error traces when failing to get a system resource so that
it is not printed on failure with deferred probing.
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Link: https://lore.kernel.org/r/20200129153628.29329-4-amelie.delaunay@st.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/stm32-dma.c

@@ -1296,8 +1296,10 @@ static int stm32_dma_probe(struct platform_device *pdev)
 
 	dmadev->clk = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(dmadev->clk)) {
-		dev_err(&pdev->dev, "Error: Missing controller clock\n");
-		return PTR_ERR(dmadev->clk);
+		ret = PTR_ERR(dmadev->clk);
+		if (ret != -EPROBE_DEFER)
+			dev_err(&pdev->dev, "Can't get clock\n");
+		return ret;
 	}
 
 	ret = clk_prepare_enable(dmadev->clk);
@@ -1310,7 +1312,11 @@ static int stm32_dma_probe(struct platform_device *pdev)
 						"st,mem2mem");
 
 	rst = devm_reset_control_get(&pdev->dev, NULL);
-	if (!IS_ERR(rst)) {
+	if (IS_ERR(rst)) {
+		ret = PTR_ERR(rst);
+		if (ret == -EPROBE_DEFER)
+			goto clk_free;
+	} else {
 		reset_control_assert(rst);
 		udelay(2);
 		reset_control_deassert(rst);
@@ -1470,10 +1476,11 @@ static struct platform_driver stm32_dma_driver = {
 		.of_match_table = stm32_dma_of_match,
 		.pm = &stm32_dma_pm_ops,
 	},
+	.probe = stm32_dma_probe,
 };
 
 static int __init stm32_dma_init(void)
 {
-	return platform_driver_probe(&stm32_dma_driver, stm32_dma_probe);
+	return platform_driver_register(&stm32_dma_driver);
 }
 subsys_initcall(stm32_dma_init);