[PATCH v6 06/12] 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.ray...@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 
90b70529a478d11d907cbd6b64d680d0c1db4d5c..4b3d812f9c6539a6b769990e3e11f14f49abb2a9
 100644
--- a/drivers/clk/clk-uclass.c
+++ b/drivers/clk/clk-uclass.c
@@ -623,14 +623,27 @@ 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)

-- 
2.48.1