Messages in this thread | | | Date | Thu, 12 Jan 2012 10:07:02 +0000 | From | Jamie Iles <> | Subject | Re: [RFC v2 4/9] of: add clock providers |
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On Wed, Jan 11, 2012 at 09:46:58PM -0700, Grant Likely wrote: > On Tue, Jan 10, 2012 at 2:33 PM, Jamie Iles <jamie@jamieiles.com> wrote: > > On Mon, Dec 12, 2011 at 03:02:04PM -0700, Grant Likely wrote: > >> +- clock-output-names : From common clock binding > >> + > >> +Example: > >> + clock { > >> + compatible = "fixed-clock"; > >> + #clock-cells = <0>; > >> + clock-frequency = <1000000000>; > >> + }; > > > > I wonder if this should have an optional clock consumer with a standard > > name for parenting? For example, on picoxcell there is a fixed 200MHz > > APB clock that is really a PLL from a 20MHz reference input and I'd like > > to represent that in the clock tree. > > If it depends on a parent clock, then it really isn't a fixed clock, > is it (from the perspective of the OS). The point of this binding is > a trivial way to describe clocks that don't change. If that > assumption doesn't hold true, then this binding isn't suitable for > that clock. As you point out, even the gpio enable feature is pushing > things a bit. > > That said, I'm open to extending this binding if something can be > defined that will have a lot of use cases.
Well for picoxcell where the 200MHz APB clock is just a PLL generated from a 20MHz clock then it kind of is a fixed clock as far as Linux is concerned isn't it? The rate can't be changed and and the clock can't be disabled so it's just a dumb clock with a parent.
I guess I could just omit the parent as far as Linux is concerned, but it would be nice to represent the real clock tree if possible.
> > I'm about to start trying to get this and Mike's common struct clk > > patches working on picoxcell, and the one thing I'm not understanding at > > the moment is how to handle the tree itself. Currently I was planning > > on iterating over all clocks and finding a named input clock "ref" or > > "input" perhaps. This would be fine for picoxcell, but I guess more > > complicated chips may need something else. > > It might be useful to have something like of_irq_init() for setting up > initial clocks, but the solution feels inelegant to me. I suspect > that there will be end up being intertwined init order dependencies > between clocks and irqs and other early setup stuff that could be > handled better. Again, I need to think about this some more. There > might need to be something like an of_early_probe() call that accepts > a match table of compatible values and setup functions with some logic > or data to resolve dependencies. The trick will be to not end up with > something complex. I'll need to think about this more...
Yes, probably not an easy problem to solve, especially for the platforms where the parent can change at runtime.
I wonder if an of_clk_init() could take a platform callback, so that of_clk_init() goes of and creates a struct clk for each clk in the DT, then for each registered clock calls a platform specific callback which returns the parent (if any). It feels like a fairly platform specific problem to me.
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