Hi Mark, On Tue, Apr 04, 2023 at 04:26:18PM +0100, Mark Brown wrote: > On Tue, Apr 04, 2023 at 12:11:33PM +0200, Maxime Ripard wrote: > > The tlv320aic32x4 clkin 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. > > It could be configured from device tree as well couldn't it? Yep, indeed. > > 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(). > > Historically clk_set_rate() wouldn't reparent IIRC. > > > 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. > > To be honest it's surprising that we'd have to manually specify this, I > would expect to be able to reparent. I suspect it'd be better to go the > other way here and allow reparenting. Yeah, I think I'd prefer to allow reparenting too, but as can be seen from the other reviewers in that thread, it seems like we have a very split community here, so that doesn't sound very realistic without some major pushback :) Maxime
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