[PATCH v4 2/2] dmaengine: dw-axi-dmac: add reset control support

[Artem Shimko <a.shimko.dev@gmail.com>]

Add proper reset control handling to the AXI DMA driver to ensure
reliable initialization and power management. The driver now manages
resets during probe, remove, and system suspend/resume operations.

The implementation stores reset control in the chip structure and adds
reset assert/deassert calls at the appropriate points: resets are
deasserted during probe after clock acquisition, asserted during remove
and error cleanup, and properly managed during suspend/resume cycles.
Additionally, proper error handling is implemented for reset control
operations to ensure robust behavior.

This ensures the controller is properly reset during power transitions
and prevents potential issues with incomplete initialization.

Signed-off-by: Artem Shimko <a.shimko.dev@gmail.com>
---
 .../dma/dw-axi-dmac/dw-axi-dmac-platform.c    | 50 +++++++++++++------
 drivers/dma/dw-axi-dmac/dw-axi-dmac.h         |  1 +
 2 files changed, 35 insertions(+), 16 deletions(-)

diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
index 8b7cf3baf5d3..a3e93b658c21 100644
--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
@@ -1316,11 +1316,16 @@ static int dma_chan_resume(struct dma_chan *dchan)
 
 static int axi_dma_suspend(struct device *dev)
 {
+	int ret;
 	struct axi_dma_chip *chip = dev_get_drvdata(dev);
 
 	axi_dma_irq_disable(chip);
 	axi_dma_disable(chip);
 
+	ret = reset_control_assert(chip->resets);
+	if (ret)
+		dev_warn(dev, "Failed to assert resets, but continuing suspend\n");
+
 	clk_disable_unprepare(chip->core_clk);
 	clk_disable_unprepare(chip->cfgr_clk);
 
@@ -1340,6 +1345,10 @@ static int axi_dma_resume(struct device *dev)
 	if (ret < 0)
 		return ret;
 
+	ret = reset_control_deassert(chip->resets);
+	if (ret)
+		return ret;
+
 	axi_dma_enable(chip);
 	axi_dma_irq_enable(chip);
 
@@ -1455,7 +1464,6 @@ static int dw_probe(struct platform_device *pdev)
 	struct axi_dma_chip *chip;
 	struct dw_axi_dma *dw;
 	struct dw_axi_dma_hcfg *hdata;
-	struct reset_control *resets;
 	unsigned int flags;
 	u32 i;
 	int ret;
@@ -1487,16 +1495,6 @@ static int dw_probe(struct platform_device *pdev)
 			return PTR_ERR(chip->apb_regs);
 	}
 
-	if (flags & AXI_DMA_FLAG_HAS_RESETS) {
-		resets = devm_reset_control_array_get_exclusive(&pdev->dev);
-		if (IS_ERR(resets))
-			return PTR_ERR(resets);
-
-		ret = reset_control_deassert(resets);
-		if (ret)
-			return ret;
-	}
-
 	chip->dw->hdata->use_cfg2 = !!(flags & AXI_DMA_FLAG_USE_CFG2);
 
 	chip->core_clk = devm_clk_get(chip->dev, "core-clk");
@@ -1507,18 +1505,28 @@ static int dw_probe(struct platform_device *pdev)
 	if (IS_ERR(chip->cfgr_clk))
 		return PTR_ERR(chip->cfgr_clk);
 
+	chip->resets = devm_reset_control_array_get_optional_exclusive(&pdev->dev);
+	if (IS_ERR(chip->resets))
+		return PTR_ERR(chip->resets);
+
+	ret = reset_control_deassert(chip->resets);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "Failed to deassert resets\n");
+
 	ret = parse_device_properties(chip);
 	if (ret)
-		return ret;
+		goto err_exit;
 
 	dw->chan = devm_kcalloc(chip->dev, hdata->nr_channels,
 				sizeof(*dw->chan), GFP_KERNEL);
-	if (!dw->chan)
-		return -ENOMEM;
+	if (!dw->chan) {
+		ret = -ENOMEM;
+		goto err_exit;
+	}
 
 	ret = axi_req_irqs(pdev, chip);
 	if (ret)
-		return ret;
+		goto err_exit;
 
 	INIT_LIST_HEAD(&dw->dma.channels);
 	for (i = 0; i < hdata->nr_channels; i++) {
@@ -1605,20 +1613,30 @@ static int dw_probe(struct platform_device *pdev)
 
 err_pm_disable:
 	pm_runtime_disable(chip->dev);
+err_exit:
+	reset_control_assert(chip->resets);
 
 	return ret;
 }
 
 static void dw_remove(struct platform_device *pdev)
 {
+	int ret;
 	struct axi_dma_chip *chip = platform_get_drvdata(pdev);
 	struct dw_axi_dma *dw = chip->dw;
 	struct axi_dma_chan *chan, *_chan;
 	u32 i;
 
-	/* Enable clk before accessing to registers */
+	/*
+	 * The peripheral must be clocked and out of reset
+	 * before its registers can be accessed.
+	 */
 	clk_prepare_enable(chip->cfgr_clk);
 	clk_prepare_enable(chip->core_clk);
+	ret = reset_control_deassert(chip->resets);
+	if (ret)
+		dev_err(&pdev->dev, "Failed to deassert resets\n");
+
 	axi_dma_irq_disable(chip);
 	for (i = 0; i < dw->hdata->nr_channels; i++) {
 		axi_chan_disable(&chip->dw->chan[i]);
diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac.h b/drivers/dma/dw-axi-dmac/dw-axi-dmac.h
index b842e6a8d90d..c74affb9f344 100644
--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac.h
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac.h
@@ -71,6 +71,7 @@ struct axi_dma_chip {
 	struct clk		*core_clk;
 	struct clk		*cfgr_clk;
 	struct dw_axi_dma	*dw;
+	struct reset_control	*resets;
 };
 
 /* LLI == Linked List Item */
-- 
2.43.0