linux-kernel - Re: [PATCH v2 4/4] arm64: dts: qcom: sm6350: Add video clock controller

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Message-Id: <DAIQVM2164NF.35T50MSWTTQWG@fairphone.com>
Date: Tue, 10 Jun 2025 11:27:19 +0200
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Konrad Dybcio" <konrad.dybcio@....qualcomm.com>, "Taniya Das"
 <quic_tdas@...cinc.com>, "Jagadeesh Kona" <quic_jkona@...cinc.com>, "Bjorn
 Andersson" <andersson@...nel.org>, "Michael Turquette"
 <mturquette@...libre.com>, "Stephen Boyd" <sboyd@...nel.org>, "Rob Herring"
 <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>, "Conor
 Dooley" <conor+dt@...nel.org>, "Konrad Dybcio" <konradybcio@...nel.org>
Cc: <~postmarketos/upstreaming@...ts.sr.ht>, <phone-devel@...r.kernel.org>,
 <linux-arm-msm@...r.kernel.org>, <linux-clk@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] arm64: dts: qcom: sm6350: Add video clock
 controller

Hi Konrad and all,

On Tue Apr 15, 2025 at 11:13 AM CEST, Konrad Dybcio wrote:
> On 4/15/25 6:05 AM, Taniya Das wrote:
>> 
>> 
>> On 4/12/2025 12:56 AM, Konrad Dybcio wrote:
>>> On 4/11/25 1:37 PM, Jagadeesh Kona wrote:
>>>>
>>>>
>>>> On 4/11/2025 2:42 PM, Konrad Dybcio wrote:
>>>>> On 4/11/25 9:15 AM, Jagadeesh Kona wrote:
>>>>>>
>>>>>>
>>>>>> On 4/1/2025 10:03 PM, Konrad Dybcio wrote:
>>>>>>> On 3/24/25 9:41 AM, Luca Weiss wrote:
>>>>>>>> Add a node for the videocc found on the SM6350 SoC.
>>>>>>>>
>>>>>>>> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
>>>>>>>> ---
>>>>>>>>  arch/arm64/boot/dts/qcom/sm6350.dtsi | 14 ++++++++++++++
>>>>>>>>  1 file changed, 14 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/arch/arm64/boot/dts/qcom/sm6350.dtsi b/arch/arm64/boot/dts/qcom/sm6350.dtsi
>>>>>>>> index 42f9d16c2fa6da66a8bb524a33c2687a1e4b40e0..4498d6dfd61a7e30a050a8654d54dae2d06c220c 100644
>>>>>>>> --- a/arch/arm64/boot/dts/qcom/sm6350.dtsi
>>>>>>>> +++ b/arch/arm64/boot/dts/qcom/sm6350.dtsi
>>>>>>>> @@ -1952,6 +1952,20 @@ usb_1_dwc3_ss_out: endpoint {
>>>>>>>>  			};
>>>>>>>>  		};
>>>>>>>>  
>>>>>>>> +		videocc: clock-controller@...0000 {
>>>>>>>> +			compatible = "qcom,sm6350-videocc";
>>>>>>>> +			reg = <0x0 0x0aaf0000 0x0 0x10000>;
>>>>>>>> +			clocks = <&gcc GCC_VIDEO_AHB_CLK>,
>>>>>>>> +				 <&rpmhcc RPMH_CXO_CLK>,
>>>>>>>> +				 <&sleep_clk>;
>>>>>>>> +			clock-names = "iface",
>>>>>>>> +				      "bi_tcxo",
>>>>>>>> +				      "sleep_clk";
>>>>>>>> +			#clock-cells = <1>;
>>>>>>>> +			#reset-cells = <1>;
>>>>>>>> +			#power-domain-cells = <1>;
>>>>>>>> +		};
>>>>>>>
>>>>>>> You'll probably want to hook up some additional power domains here, see
>>>>>>>
>>>>>>> https://lore.kernel.org/linux-arm-msm/20250327-videocc-pll-multi-pd-voting-v3-0-895fafd62627@quicinc.com/
>>>>>>>
>>>>>>
>>>>>> On SM6350, videocc doesn't need multiple power domains at HW level, it is only on CX rail which would be ON
>>>>>> when system is active, hence power-domains are not mandatory here.
>>>>>
>>>>> 6350 doesn't have either MMCX nor a split MX - shouldn't both normal
>>>>> CX and MX be in there?
>>>>>
>>>>
>>>> All clocks & GDSC's of SM6350 videocc are only on CX rail, so it requires only CX power domain. But when HLOS
>>>> is active, CX rail will be ON and operate at a level above retention, which is sufficient for videocc to operate.
>>>> Hence clock driver don't need to explicitly vote on CX rail.
>>>>
>>>> The same is not true for other rails like MMCX and Split MX(MXC), hence clock drivers had to explicitly vote on
>>>> those rails.
>>>
>>> I'm worried about MX being undervolted for higher OPPs
>>>
>> 
>> From a videocc PoV there is no requirement of Mx on SM6350. The CX
>> levels would be taken care by Video SW driver from their defined OPP. Mx
>> at system level would be catered via the BW votes.
>
> So I'm specifically thinking about the videocc (and other) PLLs, which
> have defined vdd levels downstream - currently we're relying on random
> luck rather than ensuring each one of them has its requirements fulfilled

Any further comments than this? Not sure how to proceed.

Regards
Luca