Messages in this thread | | | Date | Tue, 13 Jun 2023 17:30:06 +0200 | Subject | Re: [PATCH 1/2] clk: sunxi-ng: nkm: consider alternative parent rates when finding rate | From | Maxime Ripard <> |
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On Tue, Jun 13, 2023 at 12:17:06PM +0200, Frank Oltmanns wrote: > Hi Maxime, > > I'll now only respond to one aspect of your mail, because it's the > foundation for the whole behaviour. > > On 2023-06-13 at 11:10:08 +0200, Maxime Ripard <maxime@cerno.tech> wrote: > [...] > >> >> ccu_nkm_find_best is called in the following two situations: > >> >> a. from ccu_nkm_set_rate when setting the rate > >> >> b. from ccu_nkm_round_rate when determining the rate > >> >> > >> >> In situation a. we never want ccu_nkm_find_best to try different parent > >> >> rates because setting the parent rate is a done deal (at least that's my > >> >> understanding). > >> >> > >> >> In situation b. we only want ccu_nkm_find_best to try different parent > >> >> rates when, as you mentioned, the CLK_SET_RATE_PARENT flag is set. > >> > > >> > It doesn't really matter though. The output of that function must be > >> > stable and must return the same set of factors and parent rate for a > >> > given target rate. > >> > > >> > >> I'm not sure if we're talking about the same thing here. Of course the > >> set of factors and parent rate for a given target rate will be different > >> depending on the fact if we can or cannot adjust the parent rate, > >> agreed? > > > > Yes, but here you also have a different behaviour in clk_round_rate() > > and in clk_set_rate(), which isn't ok. > > > > Basically, clk_set_rate() + clk_get_rate() must be equal to > > clk_round_rate(). > > > > If you change if you look for parents depending on whether you're being > > called in clk_round_rate() and clk_set_rate(), then you're breaking that > > expectation. > > > >> Let me compare my implementation to ccu_mp. > >> > >> ccu_mp_round_rate either calls the function ccu_mp_find_best or > >> ccu_mp_find_best_with_parent_adj, depending on CLK_SET_RATE_PARENT. > > > > Yes, and it's fine: the flag is per-clock, and the output is the same > > depending on whether we're being called by clk_round_rate() and > > clk_set_rate(). > > > > The output is really not the same. > > ccu_mp_set_rate() always calls ccu_mp_find_best(). It never (!) considers > changing the parent, independent of any flags. > > ccu_mp_round_rate() is calling ccu_mp_find_best() OR > ccu_mp_find_best_with_parent_adj() depending on the flag. > > If I understand you correctly, you consider that a bug.
No, sorry, you're right.
clk_set_rate will call round_rate first, which will (possibly) pick up a new parent, and by the time set_rate is called our parent will have been changed already so we will just call find_best again considering only that parent.
The set of factors and dividers should remain the same there, but I don't think that's a concern.
That leaves us with the rounding stuff, and the overall function arguments. I like the structure of ccu_mp better, is there a reason to deviate from it?
Maxime [unhandled content-type:application/pgp-signature] | |