Date:   Tue, 24 Jan 2017 19:45:55 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
CC:     Stephen Boyd <sboyd@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        robh+dt <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v4 3/4] dt-bindings: phy: Add support for QMP phy

Hi,

On Tuesday 24 January 2017 07:35 PM, Vivek Gautam wrote:
> On Tue, Jan 24, 2017 at 3:03 PM, Kishon Vijay Abraham I <kishon@...com> wrote:
>> Hi,
>>
>> On Friday 20 January 2017 03:12 AM, Stephen Boyd wrote:
>>> On 01/19, Vivek Gautam wrote:
>>>>
>>>> On 01/19/2017 06:10 AM, Stephen Boyd wrote:
>>>>>>
>>>>> Didn't we already move away from subnodes for lanes in an earlier
>>>>> revision of these patches? I seem to recall we did that because
>>>>> lanes are not devices and the whole "phy as a bus" concept not
>>>>> making sense.
>>>>
>>>> Yea, we started out without having any sub-nodes and we
>>>> argued that we don't require them since the qmp device is
>>>> represented by the qmp node itself.
>>>> The lanes otoh are representative of gen_phys and related properties.
>>>>
>>>> In the driver -
>>>> "struct qmp_phy " represents the lanes and holds "struct phy",
>>>> "struct qcom_qmp" represents the qmp block as a whole and holds
>>>> "struct device"
>>>> Does this make lanes qualify to be childs of qmp ?
>>>
>>> Hmm... maybe I was recalling the DSI phy binding. I think there
>>> are lanes there too but we decided to just have one node.
>>>
>>>>
>>>> "phy as a bus" (just trying to understand here) -
>>>> let's say a usb phy controller has one HSIC phy port and one USB2 phy port.
>>>> So, should this phy controller be a bus providing two ports (and so
>>>> we will have
>>>> couple of child nodes to the phy controller) ?
>>>>
>>>
>>> Typically in DT a subnode or collection of subnodes means there's
>>> some sort of bus involved. Usually each node corresponds to a
>>> struct device, and the parent node corresponds to the bus or
>>> controller for the logical bus.
>>>
>>> In this case (only PCIe though? not UFS or USB?) it seems like we
>>> have multiple phys that share a common register space, but
>>> otherwise they have their own register space and power
>>> management. Would you have each PCIe controller point to a
>>> different subnode for their associated phy? I'm trying to
>>> understand the benefit of the subnodes if they aren't treated as
>>> struct devices.
>>
>> Yes, instead of having all the controller having a phandle to the same PHY and
>> then using other mechanisms to differentiate between the PHYs, each controller
>> can have a phandle to the exact port that it is connected to.
>>
>> This also gives a better representation of the hardware and can avoid lot of
>> boilerplate code in the driver.
> 
> Below is one binding that works for me.
> --------------------
>                phy@...00 {
>                         compatible = "qcom,msm8996-qmp-pcie-phy";
>                         reg = <0x034000 0x488>;
>                         #clock-cells = <1>;
>                         #address-cells = <1>;
>                         #size-cells = <1>;
>                         ranges;
> 
>                         clocks = <&gcc GCC_PCIE_PHY_AUX_CLK>,
>                                 <&gcc GCC_PCIE_PHY_CFG_AHB_CLK>,
>                                 <&gcc GCC_PCIE_CLKREF_CLK>;
>                         clock-names = "aux", "cfg_ahb", "ref";
> 
>                         vdda-phy-supply = <&pm8994_l28>;
>                         vdda-pll-supply = <&pm8994_l12>;
> 
>                         resets = <&gcc GCC_PCIE_PHY_BCR>,
>                                 <&gcc GCC_PCIE_PHY_COM_BCR>,
>                                 <&gcc GCC_PCIE_PHY_COM_NOCSR_BCR>;
>                         reset-names = "phy", "common", "cfg";
> 
>                         pciephy_p0: port@0 {
>                                 reg = <0x035000 0x130>,
>                                         <0x035200 0x200>,
>                                         <0x035400 0x1dc>;
>                                 #phy-cells = <0>;
> 
>                                 clocks = <&gcc GCC_PCIE_0_PIPE_CLK>;
>                                 clock-names = "pipe0";
>                                 resets = <&gcc GCC_PCIE_0_PHY_BCR>;
>                                 reset-names = "lane0";
>                         };
> 
>                       pciephy_p1: port@1 {
>                                 reg = <0x036000 0x130>,
>                                         <0x036200 0x200>,
>                                         <0x036400 0x1dc>;
>                                 #phy-cells = <0>;
> 
>                                 clocks = <&gcc GCC_PCIE_1_PIPE_CLK>;
>                                 clock-names = "pipe1";
>                                 resets = <&gcc GCC_PCIE_1_PHY_BCR>;
>                                 reset-names = "lane1";
>                         };
> 
>                         pciephy_p2: port@2 {
>                                 reg = <0x037000 0x130>,
>                                         <0x037200 0x200>,
>                                         <0x037400 0x1dc>;
>                                 #phy-cells = <0>;
> 
>                                 clocks = <&gcc GCC_PCIE_2_PIPE_CLK>;
>                                 clock-names = "pipe2";
>                                 resets = <&gcc GCC_PCIE_2_PHY_BCR>;
>                                 reset-names = "lane2";
>                         };
>                 };
> --------------------
> 
> let me know if this looks okay.

looks good to me.

Thanks
Kishon

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