On Thu, Aug 22, 2013 at 08:19:10AM +0100, Mike Turquette wrote:
Quoting Tomasz Figa (2013-08-21 14:34:55)
On Wednesday 21 of August 2013 09:50:15 Mark Rutland wrote:
On Tue, Aug 20, 2013 at 01:06:25AM +0100, Mike Turquette wrote:
Quoting Mark Rutland (2013-08-19 02:35:43)
On Sat, Aug 17, 2013 at 04:17:18PM +0100, Tomasz Figa wrote:
On Saturday 17 of August 2013 16:53:16 Sascha Hauer wrote: > On Sat, Aug 17, 2013 at 02:28:04PM +0200, Tomasz Figa wrote: > > > > > Also I would make this option required. Use a dummy > > > > > clock for > > > > > mux > > > > > inputs that are grounded for a specific SoC. > > > > > > > > Some clocks are not from CCM and we haven't defined in > > > > imx6q-clk.txt, > > > > so in most cases we can't provide a phandle for them, eg: > > > > spdif_ext. > > > > I think it's a bit hard to force it to be 'required'. An > > > > 'optional' > > > > looks more flexible to me and a default one is ensured > > > > even if > > > > it's > > > > missing. > > > > > > <&clks 0> is the dummy clock. This can be used for all input > > > clocks > > > not > > > defined by the SoC. > > > > Where does this assumption come from? Is it documented > > anywhere? > > This is how all i.MX clock bindings currently are. See > Documentation/devicetree/bindings/clock/imx*-clock.txt
OK, thanks.
I guess we need some discussion on dummy clocks vs skipped clocks. I think we want some consistency on this, don't we?
If we really need a dummy clock, then we might also want a generic way to specify it.
What do we actually mean by a "dummy clock"? We already have bindings for "fixed-clock" and co friends describe relatively simple preconfigured clocks.
Some platforms have a fake clock which defines noops callbacks and basically doesn't do anything. This is analogous to the dummy regulator implementation. A central one could be registered by the clock core, as is done by the regulator core.
When you say some platforms, you presumably mean the platform code in Linux? A dummy clock sounds like a completely Linux-specific abstraction rather than a description of the hardware, and I don't see why we need that in the DT:
- If a clock is wired up and running (as presumably the dummy clock is),
then surely it's a fixed-clock (it's running, we and we have no control over it, but we presumably know its rate) and can be described as such?
- If no clock is wired up, then we should be able to describe that. If a
driver believes that a clock is required when it isn't (for some level of functionality), then that driver should be fixed up to support the clock as being optional.
Am I missing something?
I second that.
Moreover, I don't think that device tree should deal with dummy anything. It should be able to describe hardware that is available on given system, not list what hardware is not available.
I wasn't clear. The dummy clock IS a completely Linux-specific abstraction.
I'm not advocating a dummy clock in DT. I am advocating consolidation of the implementation of a clock that does nothing into the clock core. This code could easily live in drivers/clk/clk.c instead of having everyone open-code it.
As far as specifying a dummy clock in DT? I dunno. DT should describe real hardware so there isn't much use for a dummy clock.
Sorry, I misunderstood. Good to hear we're on the same page :)
I'm guessing one of the reasons for such a clock are drivers do not honor the clk.h api and they freak out when clk_get gives them a NULL pointer?
I'm not sure. Sascha, could you shed some light on the matter?
Thanks, Mark.