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Subject: Re: [PATCH 1/2] dt-bindings: power: Add ZynqMP power domain
 bindings
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Rob Herring <robh@kernel.org>
Cc:     Jolly Shah <jolly.shah@xilinx.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Andy Gross <andy.gross@linaro.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        =?UTF-8?Q?Bj=c3=b6rn_Andersson?= <bjorn.andersson@linaro.org>,
        sean.wang@mediatek.com, Michal Simek <michal.simek@xilinx.com>,
        Mark Rutland <mark.rutland@arm.com>, rajanv@xilinx.com,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jolly Shah <jollys@xilinx.com>
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-id: <d47ed37f-057f-b510-de70-1140dad1b7ad@samsung.com>
Date:   Tue, 06 Mar 2018 09:06:24 +0100
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Hi All,

On 2018-03-06 08:59, Geert Uytterhoeven wrote:
> Hi Rob, Jolly,
>
> On Mon, Mar 5, 2018 at 11:39 PM, Rob Herring <robh@kernel.org> wrote:
>> On Tue, Feb 27, 2018 at 03:55:49PM -0800, Jolly Shah wrote:
>>> Add documentation to describe ZynqMP power domain bindings.
>>>
>>> Signed-off-by: Jolly Shah <jollys@xilinx.com>
>>> Signed-off-by: Rajan Vaja <rajanv@xilinx.com>
>>> ---
>>>   .../devicetree/bindings/power/zynqmp-genpd.txt     | 46 ++++++++++++++++++++++
>>>   1 file changed, 46 insertions(+)
>>>   create mode 100644 Documentation/devicetree/bindings/power/zynqmp-genpd.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/power/zynqmp-genpd.txt b/Documentation/devicetree/bindings/power/zynqmp-genpd.txt
>>> new file mode 100644
>>> index 0000000..25f9711
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/power/zynqmp-genpd.txt
>>> +This node contains a number of subnodes, each representing a single PM domain
>>> +that PM domain consumer devices reference.
>>> +
>>> +== PM Domain Nodes ==
>>> +
>>> +Required properties:
>>> + - #power-domain-cells: Number of cells in a PM domain specifier. Must be 0.
>>> + - pd-id: List of domain identifiers of as defined by platform firmware. These
>>> +       identifiers are passed to the PM firmware.
>>> +
>>> +Example:
>>> +     zynqmp-genpd {
>>> +             compatible = "xlnx,zynqmp-genpd";
>> What's the control interface for controlling the domains?
>>> +
>>> +             pd_usb0: pd-usb0 {
>>> +                     pd-id = <22>;
>>> +                     #power-domain-cells = <0>;
>> There's no need for all these sub nodes. Make #power-domain-cells 1 and
>> put the id in the cell value.
> That was my first reaction, too...
>>> +             };
>>> +
>>> +             pd_sata: pd-sata {
>>> +                     pd-id = <28>;
>>> +                     #power-domain-cells = <0>;
>>> +             };
>>> +
>>> +             pd_gpu: pd-gpu {
>>> +                     pd-id = <58 20 21>;
> ... until I saw the above.
> Controlling the GPU power area requires controlling 3 physical areas?
>
> However, doing it this way may bite you in the future, if a need arises to
> control a subset. And what about power up/down order?

What about defining 3 separate domains and arranging them in parent-child
relationship? generic power domains already supports that and this allows
to nicely define the power on/off order.

>>> +                     #power-domain-cells = <0x0>;
>>> +             };
>>> +     };

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland