linux-kernel - Re: [PATCH V4 8/8] arm64: dts: qcom: sm4450: add camera, display and gpu clock controller

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Message-ID: <8f7cdb31-c50d-4690-b878-518bad545612@linaro.org>
Date: Fri, 12 Jul 2024 14:22:27 +0200
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Ajit Pandey <quic_ajipan@...cinc.com>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
 Vinod Koul <vkoul@...nel.org>,
 Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 Taniya Das <quic_tdas@...cinc.com>, Jagadeesh Kona <quic_jkona@...cinc.com>,
 Imran Shaik <quic_imrashai@...cinc.com>,
 Satya Priya Kakitapalli <quic_skakitap@...cinc.com>
Subject: Re: [PATCH V4 8/8] arm64: dts: qcom: sm4450: add camera, display and
 gpu clock controller

On 12.07.2024 11:53 AM, Ajit Pandey wrote:
> 
> 
> On 7/11/2024 3:25 PM, Konrad Dybcio wrote:
>> On 3.07.2024 11:16 AM, Ajit Pandey wrote:
>>>
>>>
>>> On 6/13/2024 1:11 PM, Konrad Dybcio wrote:
>>>>
>>>>
>>>> On 6/11/24 15:37, Ajit Pandey wrote:
>>>>> Add device node for camera, display and graphics clock controller on
>>>>> Qualcomm SM4450 platform.
>>>>>
>>>>> Signed-off-by: Ajit Pandey <quic_ajipan@...cinc.com>
>>>>> ---
>>>>
>>>> None of these nodes reference a power domain (which would usually be
>>>> CX/MX/MMCX). This way, the RPMhPDs will never be scaled.
>>>>
>>>> The current upstream implementation only allows one power domain to be
>>>> scaled, but that's better than none (see other DTs for recent SoCs).
>>>>
>>>> Konrad
>>>
>>> SM4450 doesn't support MMCX and CX/MX domains will remain active so
>>> power-domains property is actually not required for SM4450 clock nodes.
>>
>> It's not only about them being active.. some PLLs require e.g. MX to be
>> at a certain level, or the system will be unstable
>>
>> Konrad
> 
> With active I mean CX/MX rails will be default running at minimum level required for clock controllers. Adding power-domains property for CX/MX rails is like a redundant code as that will also scale such rails at default specified minimum level only. Also we hadn't added such property for other targets DT nodes to scale up CX/MX at minimum level.

What I mean here is that, the minimum level may not be enough. In such case
you would also add a required-opps = <&handle_to_rpmhpd_opp_level>

Konrad