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    SubjectRe: Strange location and name for platform devices when device-tree is used.
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    On Fri, 2013-11-01 at 15:22 +1100, Benjamin Herrenschmidt wrote:
    > On Fri, 2013-11-01 at 14:59 +1100, NeilBrown wrote:
    > > and I wonder how relevant it still is in this context. As platform devices
    > > are all in the root of the device-tree and hence are siblings, they must have
    > > unique names in the device-tree and so the platform devices created from
    > > them will also have unique names -- won't they?
    >
    > I agree about /sys/devices -> /sys/devices/platform, that makes more
    > sense
    >
    > The problem with names is that we don't *know* that your devices are
    > at the root and unique. They don't have to be. I have platforms that
    > have several "chips" each containing all the same devices. They need to
    > be de-duped.
    >
    > Maybe the right approach is to build the de-duplication in sysfs
    > itself ?

    BTW. How come you have devices at the root of the tree without "reg" ?
    It's fairly fishy ...

    The root of the tree is supposed to represent the processor address
    space, and has #address-cells/#size-cells set appropriately. Any MMIO
    mapped device shall thus have a "reg" property and a unit address.

    Only "container" nodes (such as /cpus or /chosen) or virtual devices
    (such as a node used to representing the collection of bits & pieces
    that makes the audio infrastructure) and are thus not per-se MMIO mapped
    entities can ommit the "reg" properties.

    In the case of pwm, it looks like there's another device providing a pwm
    capability, in which case your backlight would indeed be a "virtual
    device" (basically non-mmio device not hanging off any bus). Or it could
    have been represented as a child of pwm if that had been defined that
    way, I am not familiar with the pwm bindings.

    Cheers,
    Ben.

    > Cheers,
    > Ben.
    >
    > > Any help understanding and/or fixing this discrepancy greatly appreciated.
    > >
    > > The change of name is particularly annoying to me because one of my platform
    > > devices is a pwm_bl.c backlight. With a boardfile I
    > > get /sys/class/pwm_backlight. With devicetree the best I can get
    > > is /sys/class/pwm_backlight.23 (or similar). It would be really nice to have
    > > a more stable and sensible name here.
    >




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