[PATCH v2 06/13] clk: Ensure the parent clocks are enabled while reparenting

[Miquel Raynal]

Reparenting a clock C with a new parent P means that C will only
continue clocking if P is already clocking when the mux is updated. In
case the parent is currently disabled, failures (stalls) are likely to
happen.

This is exactly what happens on i.MX8 when enabling the video
pipeline. We tell LCDIF clocks to use the VIDEO PLL as input, while the
VIDEO PLL is currently off. This all happens as part of the
assigned-clocks handling procedure, where the reparenting happens before
the enable() calls. Enabling the parents as part of the reparenting
procedure seems sane and also matches the logic applied in other parts
of the CCM.

Signed-off-by: Miquel Raynal <miquel.raynal at bootlin.com>
---
 drivers/clk/clk-uclass.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/clk-uclass.c b/drivers/clk/clk-uclass.c
index a9937c22dcb6bcc90b14f748a0758810a7435d61..dc89e3071130f1e1c98001a955c4fec210aa5b47 100644
--- a/drivers/clk/clk-uclass.c
+++ b/drivers/clk/clk-uclass.c
@@ -593,14 +593,27 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
 	if (!ops->set_parent)
 		return -ENOSYS;
 
-	ret = ops->set_parent(clk, parent);
-	if (ret)
+	ret = clk_enable(parent);
+	if (ret) {
+		printf("Cannot enable parent %s\n", parent->dev->name);
 		return ret;
+	}
 
-	if (CONFIG_IS_ENABLED(CLK_CCF))
+	ret = ops->set_parent(clk, parent);
+	if (ret) {
+		clk_disable(parent);
+		return ret;
+	}
+
+	if (CONFIG_IS_ENABLED(CLK_CCF)) {
 		ret = device_reparent(clk->dev, parent->dev);
+		if (ret) {
+			clk_disable(parent);
+			return ret;
+		}
+	}
 
-	return ret;
+	return 0;
 }
 
 int clk_enable(struct clk *clk)

-- 
2.47.0