On Tue, 5 Jul 2016, Julien Grall wrote: > On 05/07/16 15:04, Stefano Stabellini wrote: > > On Tue, 5 Jul 2016, Julien Grall wrote: > > > On 05/07/16 14:53, Stefano Stabellini wrote: > > > > On Thu, 30 Jun 2016, Dirk Behme wrote: > > > > > +- clocks: one or more clocks to be registered. > > > > > + Xen hypervisor drivers might replace native drivers, resulting in > > > > > + clocks not registered by these native drivers. To avoid that these > > > > > + unregistered clocks are disabled, then, e.g. by > > > > > clk_disable_unused(), > > > > > + register them in the hypervisor node. > > > > > + An example for this are the clocks of the serial driver. If the > > > > > clocks > > > > > + used by the serial hardware interface are not registered by the > > > > > serial > > > > > + driver the serial output might stop once clk_disable_unused() is > > > > > called. > > > > > > > > What if we use the "status" property of the clocks? Could we set it to > > > > "disabled" in Xen? Would that be enough for Linux to leave them alone? > > > > > > clocks could be shared between multiple devices. So it is not possible to > > > disable the clock. > > > > To clarify my suggestion: I am not saying we should disable the clock, I > > am saying we should set the "status" property to "disabled" in Xen for > > the clock used by the serial or passthrough devices (for which the > > "status" property is already set to "disabled"). That should work for > > cases where the clock is not shared among multiple devices. > > How would you be able to differentiate in Xen between a clock shared and a > non-shared one? The only way I can think it going through all the device tree > which sounds really expensive. Yes, but it is only done once and we only need to do the search for clocks of "disabled" devices. > > If the clock is shared, then I don't think we would run into the issue > > described by Dirk because I wouldn't imagine clk_disable_unused would > > try to disable the clock anymore, because it would actually be in use > > from Linux POV. > > We also want to prevent Linux changing the rate of the clock (see Mark's mail > [1]). I am not sure what's the best way to achieve that for clocks shared across multiple devices. Let's see what the clock maintainers suggest. -- 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
