linux-kernel - Re: [PATCH v4 1/2] arm64: dts: qcom: qcs8300: add display dt nodes for MDSS, DPU, DisplayPort and eDP PHY

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Message-ID: <7fddb531-51a5-4ee3-9626-3e59f1dac364@oss.qualcomm.com>
Date: Tue, 5 Aug 2025 14:30:54 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Yongxing Mou <quic_yongmou@...cinc.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] arm64: dts: qcom: qcs8300: add display dt nodes
 for MDSS, DPU, DisplayPort and eDP PHY

On 8/5/25 7:15 AM, Dmitry Baryshkov wrote:
> On Mon, Aug 04, 2025 at 02:34:56PM +0200, Konrad Dybcio wrote:
>> On 8/4/25 6:39 AM, Yongxing Mou wrote:
>>>
>>>
>>> On 2025/7/30 18:25, Konrad Dybcio wrote:
>>>> On 7/30/25 11:49 AM, Yongxing Mou wrote:
>>>>> Add devicetree changes to enable MDSS display-subsystem,
>>>>> display-controller(DPU), DisplayPort controller and eDP PHY for
>>>>> Qualcomm QCS8300 platform.
>>>>>
>>>>> Signed-off-by: Yongxing Mou <quic_yongmou@...cinc.com>
>>>>> ---
>>>>
>>>> [...]
>>>>
>>>>> +
>>>>> +                assigned-clocks = <&dispcc MDSS_DISP_CC_MDSS_VSYNC_CLK>;
>>>>> +                assigned-clock-rates = <19200000>;
>>>>
>>>> is this necessary?
>>>>
>>> Emm, i try to remove assigned-clocks and assigned-clock-rates here, device can still work.. here we just want to keep consistent with sa8775p.
>>
>> Dmitry, do you remember whether this is some relic of the past that
>> was required at one point?
> 
> I think it was necessary for old platforms (MSM8916, MSM8939, MSM8953,
> APQ8084, MSM8974, MSM8992/94, MSM8996, MSM8998, SDM630/660), which can
> source vsync_clk_src either from the XO or from the GPLL / MMPLL.

The RCG has more than one input, but the Linux driver (checked about
half of the ones you listed) only lists the XO-derived frequency so I'm
not sure it was ever *really* an issue

Konrad