The STM32F4 mux clock implements a mux with a set_parent hook, but doesn't provide a determine_rate implementation.
This is a bit odd, since set_parent() is there to, as its name implies, change the parent of a clock. However, the most likely candidate to trigger that parent change is a call to clk_set_rate(), with determine_rate() figuring out which parent is the best suited for a given rate.
The other trigger would be a call to clk_set_parent(), but it's far less used, and it doesn't look like there's any obvious user for that clock.
So, the set_parent hook is effectively unused, possibly because of an oversight. However, it could also be an explicit decision by the original author to avoid any reparenting but through an explicit call to clk_set_parent().
The latter case would be equivalent to setting the flag CLK_SET_RATE_NO_REPARENT, together with setting our determine_rate hook to __clk_mux_determine_rate(). Indeed, if no determine_rate implementation is provided, clk_round_rate() (through clk_core_round_rate_nolock()) will call itself on the parent if CLK_SET_RATE_PARENT is set, and will not change the clock rate otherwise. __clk_mux_determine_rate() has the exact same behavior when CLK_SET_RATE_NO_REPARENT is set.
And if it was an oversight, then we are at least explicit about our behavior now and it can be further refined down the line.
Signed-off-by: Maxime Ripard maxime@cerno.tech --- drivers/clk/clk-stm32f4.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/clk/clk-stm32f4.c b/drivers/clk/clk-stm32f4.c index 473dfe632cc5..01046437a48c 100644 --- a/drivers/clk/clk-stm32f4.c +++ b/drivers/clk/clk-stm32f4.c @@ -1045,6 +1045,7 @@ static int cclk_mux_set_parent(struct clk_hw *hw, u8 index) }
static const struct clk_ops cclk_mux_ops = { + .determine_rate = __clk_mux_determine_rate, .get_parent = cclk_mux_get_parent, .set_parent = cclk_mux_set_parent, }; @@ -1085,7 +1086,7 @@ static struct clk_hw *stm32_register_cclk(struct device *dev, const char *name, &mux->hw, &cclk_mux_ops, NULL, NULL, &gate->hw, &cclk_gate_ops, - flags); + flags | CLK_SET_RATE_NO_REPARENT);
if (IS_ERR(hw)) { kfree(gate);