Boris, Thanks for posting this series. Bear with me as I'm attempting to give MikeT a hand. Don't be afraid to tell me a question is stupid :-) On Wed, Nov 27, 2013 at 01:44:45PM +0100, Boris BREZILLON wrote: > This patch adds support for accuracy retrieval on fixed clocks. > It also adds a new dt property called 'clock-accuracy' to define the clock > accuracy. > > This can be usefull for oscillator (RC, crystal, ...) definitions which are > always given an accuracy characteristic. I think we need to be more explicit in the binding and the API, especially when providing a method to recalculate the accuracy. I presume this recalculated value would be relative against the root clock? There really needs to be two attributes here: the rated accuracy from the manufacturer, and the calculated accuracy wrt another clock in the system. We only need a binding for the manufacturer rating since the calculated accuracy is determined at runtime. I would also prefer to see an unknown accuracy be -1. There are already clocks on the market (PPS reference clocks) with accuracies of 0.1ppb/day [1]. Obviously, these aren't system clocks. So the limit on accuracy may be a non-issue. However, it may be worth changing the binding property to express the units. > Signed-off-by: Boris BREZILLON <b.brezillon@xxxxxxxxxxx> > --- > .../devicetree/bindings/clock/fixed-clock.txt | 3 ++ > drivers/clk/clk-fixed-rate.c | 43 +++++++++++++++++--- > include/linux/clk-provider.h | 4 ++ > 3 files changed, 44 insertions(+), 6 deletions(-) > > diff --git a/Documentation/devicetree/bindings/clock/fixed-clock.txt b/Documentation/devicetree/bindings/clock/fixed-clock.txt > index 0b1fe78..48ea0ad 100644 > --- a/Documentation/devicetree/bindings/clock/fixed-clock.txt > +++ b/Documentation/devicetree/bindings/clock/fixed-clock.txt > @@ -10,6 +10,8 @@ Required properties: > - clock-frequency : frequency of clock in Hz. Should be a single cell. > > Optional properties: > +- clock-accuracy : accuracy of clock in ppb (parts per billion). > + Should be a single cell. I would prefer to call this property 'clock-rated-ppb'. > - gpios : From common gpio binding; gpio connection to clock enable pin. > - clock-output-names : From common clock binding. > > @@ -18,4 +20,5 @@ Example: > compatible = "fixed-clock"; > #clock-cells = <0>; > clock-frequency = <1000000000>; > + clock-accuracy = <100>; > }; thx, Jason. [1] http://www.vectron.com/products/modules/md-010.htm -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
