linux-kernel - Re: [PATCH v2] arm64: dts: qcom: sdm845-xiaomi-beryllium: Add DSI and panel bits

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Message-ID: <9bbeb403-2937-aebd-91ff-5682f9112dee@somainline.org>
Date:   Mon, 8 Feb 2021 15:41:23 +0100
From:   Konrad Dybcio <konrad.dybcio@...ainline.org>
To:     Amit Pundir <amit.pundir@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        dt <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>, phone-devel@...r.kernel.org
Subject: Re: [PATCH v2] arm64: dts: qcom: sdm845-xiaomi-beryllium: Add DSI and
 panel bits


>>> +      ports {
>>> +              port@1 {
>>> +                      endpoint {
>>> +                              remote-endpoint = <&tianma_nt36672a_in_0>;
>>> +                              data-lanes = <0 1 2 3>;
>>> +                      };
>>> +              };
>>> +      };
>> The endpoint has a label, you can simply use &dsi0_out {};.
> I didn't get what you meant there. Care to point to some reference dts
> snippet please?

sdm845.dtsi, L4139 as of v5.11-rc7:


port@1 {
                        reg = <1>;
                        dsi0_out: endpoint {
                        };
                    };


This means you can essentially do:

&dsi0_out {

    remote-endpoint = <&tianma_nt36672a_in_0>;
    lanes = <0 1 2 3>;

};


in your dt :)


>>> +              vddpos-supply = <&lab>;
>>> +              vddneg-supply = <&ibb>;
>> With Angelo's latest series [1] merged in, I reckon you should explicitly configure lab/ibb (like in [2]),
>> as wrong settings (which CAN BE SET BY THE BOOTLOADER in some instances!!) can lead to hardware damage.
> So iirc in the case of beryllium device, these regulators are pre set
> by the bootloader and I can't find any reference of we
> setting/resetting it explicitly to switch ON the panel and display. So
> far default lab/ibb nodes are working fine for us and I'm hesitant to
> tinker around anything regulator related that can potentially damage
> the hardware. Having said that, I do see lab/ibb nodes being set in
> the downstream dts, with relevant soft-start and discharge-resistor
> properties and I can try switching to that once the new lab/ibb
> changes land upstream.
>
> Regards,
> Amit Pundir
>
I understand your concerns, however we actually did find out that at least one device had LAB/IBB set up by the bootloader in a way that could potentially damage the electronics, so I'm just making you aware. If it works as-is, it's probably OK.


Konrad