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

[Vinayak Kale]

On Mon, Mar 17, 2014 at 5:14 PM, Mark Rutland <mark.rutland at arm.com> wrote:
> 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.

Okay, will add the new string in next version.

For documentation of bindings for "apm,potenza-pmu", can I insert it
in existing arm-pmu bindings file
(i.e.Documentation/devicetree/bindings/arm/pmu.txt) or shall I create
new file?

>
> Cheers,
> Mark.