Messages in this thread | | | Date | Wed, 21 May 2014 09:34:57 +0200 | From | Uwe Kleine-König <> | Subject | Re: [RFC PATCH 2/5] clk: Introduce 'clk_round_rate_nearest()' |
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Hello,
On Tue, May 20, 2014 at 02:48:20PM -0700, Sören Brinkmann wrote: > On Tue, 2014-05-20 at 10:48AM -0700, Stephen Boyd wrote: > > On 05/20/14 09:01, Sören Brinkmann wrote: > > > > > >>>>> +{ > > >>>>> + unsigned long lower, upper, cur, lower_last, upper_last; > > >>>>> + > > >>>>> + lower = clk_round_rate(clk, rate); > > >>>>> + if (lower >= rate) > > >>>>> + return lower; > > >>>> Is the >-case worth a warning? > > >>> No, it's correct behavior. If you request a rate that is way lower than what the > > >>> clock can generate, returning something larger is perfectly valid, IMHO. > > >>> Which reveals one problem in this whole discussion. The API does not > > >>> require clk_round_rate() to round down. It is actually an implementation > > >>> choice that had been made for clk-divider. > > >> I'm sure it's more than an implementation choice for clk-divider. But I > > >> don't find any respective documentation (but I didn't try hard). > > > A similar discussion - without final conclusion: > > > https://lkml.org/lkml/2010/7/14/260 > > > > > > > > > > Please call this new API something like clk_find_nearest_rate() or > > something. clk_round_rate() is supposed to return the rate that will be > > set if you call clk_set_rate() with the same arguments. It's up to the > > implementation to decide if that means rounding the rate up or down or > > to the nearest value. > > Sounds good to me. Are there any cases of clocks that round up? I think > that case would not be handled correctly. But I also don't see a use > case for such an implementation. I don't really care which semantic (i.e. round up, round down or round closest) is picked, but I'd vote that all should pick up the same. I think the least surprising definition is to choose rounding down and add the function that is under discussion here to get a nearest match.
So I suggest:
- if round_rate is given a rate that is smaller than the smallest available rate, return 0 - add WARN_ONCE to round_rate and set_rate if they return with a rate bigger than requested - change the return values to unsigned long
Do we also need a round_up implementation?
Mike? Russell? Any thoughts from your side?
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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