Hi Mark,

On Fri, Nov 04, 2022 at 03:44:53PM +0000, Mark Brown wrote:
> 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.

That would be another solution indeed. The thing is, most places where
determine_rate is missing seems to be oversight, and the flag is missing
as well.

Just filling determine_rate if it's missing with
__clk_mux_determine_rate will possibly pick different parents, and I'm
fairly certain that this have never been tested on most platforms, and
will be completely broken. And I don't really want to play a game of
whack-a-mole adding that flag everywhere it turns out it's broken.

Maxime