[PATCH] spi: qup: Request DMA before enabling clocks

[Stephan Gerhold <stephan@gerhold.net>]

It is usually better to request all necessary resources (clocks,
regulators, ...) before starting to make use of them. That way they do
not change state in case one of the resources is not available yet and
probe deferral (-EPROBE_DEFER) is necessary. This is particularly
important for DMA channels and IOMMUs which are not enforced by
fw_devlink yet (unless you use fw_devlink.strict=1).

spi-qup does this in the wrong order, the clocks are enabled and
disabled again when the DMA channels are not available yet.

This causes issues in some cases: On most SoCs one of the SPI QUP
clocks is shared with the UART controller. When using earlycon UART is
actively used during boot but might not have probed yet, usually for
the same reason (waiting for the DMA controller). In this case, the
brief enable/disable cycle ends up gating the clock and further UART
console output will halt the system completely.

Avoid this by requesting the DMA channels before changing the clock
state.

Fixes: 612762e82ae6 ("spi: qup: Add DMA capabilities")
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
---
 drivers/spi/spi-qup.c | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/drivers/spi/spi-qup.c b/drivers/spi/spi-qup.c
index 944ef6b42bce..00e5e88e72c4 100644
--- a/drivers/spi/spi-qup.c
+++ b/drivers/spi/spi-qup.c
@@ -1028,23 +1028,8 @@ static int spi_qup_probe(struct platform_device *pdev)
 		return -ENXIO;
 	}
 
-	ret = clk_prepare_enable(cclk);
-	if (ret) {
-		dev_err(dev, "cannot enable core clock\n");
-		return ret;
-	}
-
-	ret = clk_prepare_enable(iclk);
-	if (ret) {
-		clk_disable_unprepare(cclk);
-		dev_err(dev, "cannot enable iface clock\n");
-		return ret;
-	}
-
 	master = spi_alloc_master(dev, sizeof(struct spi_qup));
 	if (!master) {
-		clk_disable_unprepare(cclk);
-		clk_disable_unprepare(iclk);
 		dev_err(dev, "cannot allocate master\n");
 		return -ENOMEM;
 	}
@@ -1092,6 +1077,19 @@ static int spi_qup_probe(struct platform_device *pdev)
 	spin_lock_init(&controller->lock);
 	init_completion(&controller->done);
 
+	ret = clk_prepare_enable(cclk);
+	if (ret) {
+		dev_err(dev, "cannot enable core clock\n");
+		goto error_dma;
+	}
+
+	ret = clk_prepare_enable(iclk);
+	if (ret) {
+		clk_disable_unprepare(cclk);
+		dev_err(dev, "cannot enable iface clock\n");
+		goto error_dma;
+	}
+
 	iomode = readl_relaxed(base + QUP_IO_M_MODES);
 
 	size = QUP_IO_M_OUTPUT_BLOCK_SIZE(iomode);
@@ -1121,7 +1119,7 @@ static int spi_qup_probe(struct platform_device *pdev)
 	ret = spi_qup_set_state(controller, QUP_STATE_RESET);
 	if (ret) {
 		dev_err(dev, "cannot set RESET state\n");
-		goto error_dma;
+		goto error_clk;
 	}
 
 	writel_relaxed(0, base + QUP_OPERATIONAL);
@@ -1145,7 +1143,7 @@ static int spi_qup_probe(struct platform_device *pdev)
 	ret = devm_request_irq(dev, irq, spi_qup_qup_irq,
 			       IRQF_TRIGGER_HIGH, pdev->name, controller);
 	if (ret)
-		goto error_dma;
+		goto error_clk;
 
 	pm_runtime_set_autosuspend_delay(dev, MSEC_PER_SEC);
 	pm_runtime_use_autosuspend(dev);
@@ -1160,11 +1158,12 @@ static int spi_qup_probe(struct platform_device *pdev)
 
 disable_pm:
 	pm_runtime_disable(&pdev->dev);
+error_clk:
+	clk_disable_unprepare(cclk);
+	clk_disable_unprepare(iclk);
 error_dma:
 	spi_qup_release_dma(master);
 error:
-	clk_disable_unprepare(cclk);
-	clk_disable_unprepare(iclk);
 	spi_master_put(master);
 	return ret;
 }

---
base-commit: 5e41763e97db00125dec847e54a1827436d34cd3
change-id: 20230518-spi-qup-clk-defer-dfa3ce6130e3

Best regards,
-- 
Stephan Gerhold <stephan@gerhold.net>