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    SubjectRe: [PATCH v5 2/4] devicetree: bindings: Document Krait CPU/L1 EDAC
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    On Feb 25, 2014, at 5:16 AM, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote:

    > Hi Stephen,
    >
    > On Wed, Feb 19, 2014 at 12:20:43AM +0000, Stephen Boyd wrote:
    >> (Sorry, this discussion stalled due to merge window + life events)
    >
    > Sorry for the delay in replying on my side too.
    >
    >> On 01/17, Lorenzo Pieralisi wrote:
    >>> On Thu, Jan 16, 2014 at 07:26:17PM +0000, Stephen Boyd wrote:
    >>>> On 01/16, Lorenzo Pieralisi wrote:
    >>>>> On Thu, Jan 16, 2014 at 06:05:05PM +0000, Stephen Boyd wrote:
    >>>>>> On 01/16, Lorenzo Pieralisi wrote:
    >>>>>>> Do we really want to do that ? I am not sure. A cpus node is supposed to
    >>>>>>> be a container node, we should not define this binding just because we
    >>>>>>> know the kernel creates a platform device for it then.
    >>>>>>
    >>>>>> This is just copying more of the ePAPR spec into this document.
    >>>>>> It just so happens that having a compatible field here allows a
    >>>>>> platform device to be created. I don't see why that's a problem.
    >>>>>
    >>>>> I do not see why you cannot define a node like pmu or arch-timer and stick
    >>>>> a compatible property in there. cpus node does not represent a device, and
    >>>>> must not be created as a platform device, that's my opinion.
    >>>>>
    >>>>
    >>>> I had what you're suggesting before in the original revision of
    >>>> this patch. Please take a look at the original patch series[1]. I
    >>>> suppose it could be tweaked slightly to still have a cache node
    >>>> for the L2 interrupt and the next-level-cache pointer from the
    >>>> CPUs.
    >>>
    >>> Ok, sorry, we are running around in circles here, basically you moved
    >>> the node to cpus according to reviews. I still think that treating cpus
    >>> as a device is not a great idea, even though I am in the same
    >>> position with C-states and probably will add C-state tables in the cpus
    >>> node.
    >>>
    >>> http://comments.gmane.org/gmane.linux.power-management.general/41012
    >>>
    >>> I just would like to see under cpus nodes and properties that apply to
    >>> all ARM systems, and avoid defining properties (eg interrupts) that
    >>> have different meanings for different ARM cores.
    >>>
    >>> The question related to why the kernel should create a platform device
    >>> out of cpus is still open. I really do not want to block your series
    >>> for these simple issues but we have to make a decision and stick to that,
    >>> I am fine either way if we have a plan.
    >>>
    >>
    >> Do you just want a backup plan in case we don't make a platform
    >> device out of the cpus node? I believe we can always add code
    >> somewhere to create a platform device at runtime if we detect the
    >> cpus node has a compatible string equal to "qcom,krait". We could
    >> probably change this driver's module_init() to scan the DT for
    >> such a compatible string and create the platform device right
    >> there. If we get more than one interrupt in the cpus node we can
    >> add interrupt-names and then have software look for interrupts by
    >> name instead of number.
    >
    > As I mentioned, I do not like the idea of adding compatible properties
    > just to force the kernel to create platform devices out of device tree
    > nodes. On top of that I would avoid adding a compatible property
    > to the cpus node (after all properties like enable-method are common for all
    > cpus but still duplicated), my only concern being backward compatibility
    > here (ie if we do that for interrupts, we should do that also for other
    > common cpu nodes properties, otherwise we have different rules for
    > different properties).
    >
    > I think you can then add interrupts to cpu nodes ("qcom,krait" specific),
    > and as you mentioned create a platform device for that.
    >
    > Thanks,
    > Lorenzo

    So I agree with the statement about adding compatibles just to create platform devices is wrong. However its seems perfectly reasonable for a cpu node to have a compatible property. I don’t see why a CPU is any different from any other device described in a DT.

    - k

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