On Fri, Nov 04, 2022 at 02:18:00PM +0100, Maxime Ripard wrote:

> 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.

Given that the current approach involves patching every single user to
set a default implementation it feels like it might be more
straightforward to just have the clock API use that implementation if
none is defined - as you say there's already a flag to indicate the
unusual case where there's a solid reason to prevent reparenting.  It
feels like the resulting API is more straightforward.