linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: sc7280: Add Camera Control Interface busses

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Date:   Fri, 29 Sep 2023 16:52:20 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Luca Weiss <luca.weiss@...rphone.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Loic Poulain <loic.poulain@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Andi Shyti <andi.shyti@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        cros-qcom-dts-watchers@...omium.org
Cc:     ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] arm64: dts: qcom: sc7280: Add Camera Control
 Interface busses

On 29/09/2023 16:25, Konrad Dybcio wrote:
>> Not actually a required clock for the clock controller.
>>
>> I suspect the same is true for dispcc and videocc though it would also mean the respective drivers would need to switch on <&gcc DISPx_CAMERA_AHB_CLK> or <&gcc GCC_VIDEO_AHB_CLK> prior to accessing registers inside the ip blocks which may not currently be the case.
>>
>> Feels like a bit of a contrary answer but my reading is the GCC_IPBLOCK_AHB_CLK clocks belong in the drivers not the clock controllers..  or at least that's true for sm8250/camcc
> I believe the idea here would be that registering GCC_IP_AHB_CLK
> as a pm_clk for the clock controller would make that clock turn
> on when IPBLOCK_CC is accessed (e.g. when we turn on
> IPBLOCK_CORE_CLK), so that it doesn't need to be duplicated in
> each and every end device.
> 
> Konrad

Yeah I mean I accept the logic - the core AHB clock is effectively gated 
by the ipblockcc even though they originate from different places in 
hardware - and _when_ do you want one clock without the other ? Never 
except at probe() time for the ipblockcc.

Then again if you can show the clock dependency tree of camera or disp 
requires GCC_IP_AHB_CLK you could make the argument the dt requires the 
clock dependency defined in that block.

I'd say we should offline this from Luca's patches tho :) for me anyway 
the first two are fine.

Agree #3 is verboten. No new empty nodes.

---
bod