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    SubjectRe: [RFC PATCH 2/3] PM / Domains: Add support for devices with multiple domains
    Hi Jon,

    On Tue, Sep 20, 2016 at 12:28 PM, Jon Hunter <jonathanh@nvidia.com> wrote:
    > Some devices may require more than one PM domain to operate and this is
    > not currently by the PM domain framework. Furthermore, the current Linux
    > 'device' structure only allows devices to be associated with a single PM
    > domain and so cannot easily be associated with more than one. To allow
    > devices to be associated with more than one PM domain, if multiple
    > domains are defined for a given device (eg. via device-tree), then:
    > 1. Create a new PM domain for this device. The name of the new PM domain
    > created matches the device name for which it was created for.
    > 2. Register the new PM domain as a sub-domain for all PM domains
    > required by the device.
    > 3. Attach the device to the new PM domain.

    This looks a suboptimal to me: if you have n devices sharing the same PM
    domains, you would add n new subdomains?

    Having a clean way to specify multiple PM domains is very useful, though.

    E.g. on Renesas ARM SoCs, devices are usually part of two PM domains:
    1. A power area (can be "always-on",
    2. The clock domain.

    As power areas and clock domains are fairly orthogonal (the former use the
    .power_{off,on}() callbacks, the latter set GENPD_FLAG_PM_CLK and use the
    {at,de}tach_dev() callbacks), we currently setup both in the same driver
    (SYSC, for controlling power areas), which forwards the clock domain operations
    to the clock driver (CPG/MSTP or CPG/MSSR).
    Hence we have only single references in the power-domains properties, but
    having two would allow to drop the hardcoded links between the two drivers.

    (Oh no, more DT backwards compatibility issues if this is accepted ;-)

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
    -- Linus Torvalds

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