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

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Message-ID: <0db798bf-04b3-40b5-af90-7dda5b606727@quicinc.com>
Date: Tue, 15 Apr 2025 09:35:07 +0530
From: Taniya Das <quic_tdas@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Jagadeesh Kona
	<quic_jkona@...cinc.com>,
        Luca Weiss <luca.weiss@...rphone.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



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.

> Konrad