arm64: dts: Add PMU node for APM X-Gene Storm SOC

[Mark Rutland]

On Mon, Mar 17, 2014 at 11:22:55AM +0000, Vinayak Kale wrote:
> On Mon, Mar 17, 2014 at 4:03 PM, Mark Rutland <mark.rutland at arm.com> wrote:
> > On Mon, Mar 17, 2014 at 09:21:35AM +0000, Vinayak Kale wrote:
> >> This patch adds the PMU device tree node for APM X-Gene Storm SOC.
> >>
> >> Please note that this patch has dependancy on a GIC driver patch [1] which is
> >> yet to be approved by maintainers.
> >>
> >> [1]- https://lkml.org/lkml/2014/2/27/605
> >> (irqchip:gic: change access of gicc_ctrl register to read modify write)
> >>
> >> Signed-off-by: Vinayak Kale <vkale at apm.com>
> >> ---
> >>  arch/arm64/boot/dts/apm-storm.dtsi | 5 +++++
> >>  1 file changed, 5 insertions(+)
> >>
> >> diff --git a/arch/arm64/boot/dts/apm-storm.dtsi b/arch/arm64/boot/dts/apm-storm.dtsi
> >> index d37d736..587348d 100644
> >> --- a/arch/arm64/boot/dts/apm-storm.dtsi
> >> +++ b/arch/arm64/boot/dts/apm-storm.dtsi
> >> @@ -97,6 +97,11 @@
> >>               clock-frequency = <50000000>;
> >>       };
> >>
> >> +     pmu {
> >> +             compatible = "arm,armv8-pmuv3";
> >> +             interrupts = <1 12 0xff04>;
> >> +     };
> >
> > Do Potenza CPUs only have the PMUv3 events, and nothing
> > Potenza-specific?
> On top of PMUv3 events, Potenza CPU do have few implementation defined events.

Ok. So Potenza is compatible with PMUv3 (and can have it in the list),
but also has additional features for which there should be a string.

> >
> > I would have expected something like:
> >
> > compatible = "apm,potenza-pmu", "arm,armv8-pmuv3";
> PMUv3 allows to have implementation defined events. And as such the
> driver doesn't have any dependency on such events. Do you still think
> we need additional compatible string for Potenza CPU?

I do. This is precisely the reason for the compatible list. Being as
explicit as possible with the compatible list entries and having a
series of fallbacks is the sensible thing to do.

Having the additional string allows things to work now with the standard
events, and possibly later with the full set of events, without
requiring every single DTB to be updated. It also allows us to target
workarounds more precisely, for any issues we might not currently be
aware of.

Cheers,
Mark.