linux-kernel - Re: [PATCH 4/5] clk: qcom: videocc: Add support to attach multiple power domains

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Message-ID: <1d9b661e-0607-4567-b420-5444b643df99@oss.qualcomm.com>
Date: Fri, 21 Feb 2025 20:19:14 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        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: Ajit Pandey <quic_ajipan@...cinc.com>,
        Imran Shaik <quic_imrashai@...cinc.com>,
        Taniya Das <quic_tdas@...cinc.com>,
        Satya Priya Kakitapalli <quic_skakitap@...cinc.com>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] clk: qcom: videocc: Add support to attach multiple
 power domains

On 18.02.2025 4:46 PM, Bryan O'Donoghue wrote:
> On 18/02/2025 14:26, Jagadeesh Kona wrote:
>> During boot-up, the PLL configuration might be missed even after
>> calling pll_configure() from the clock controller probe. This can
>> happen because the PLL is connected to one or more rails that are
>> turned off, and the current clock controller code cannot enable
>> multiple rails during probe. Consequently, the PLL may be activated
>> with suboptimal settings, causing functional issues.
>>
>> To properly configure the video PLLs in the probe on SM8450, SM8475,
>> SM8550, and SM8650 platforms, the MXC rail must be ON along with MMCX.
>> Therefore, add support to attach multiple power domains to videocc on
>> these platforms.
>>
>> Signed-off-by: Jagadeesh Kona <quic_jkona@...cinc.com>
>> ---
>>   drivers/clk/qcom/videocc-sm8450.c | 4 ++++
>>   drivers/clk/qcom/videocc-sm8550.c | 4 ++++
>>   2 files changed, 8 insertions(+)
>>
>> diff --git a/drivers/clk/qcom/videocc-sm8450.c b/drivers/clk/qcom/videocc-sm8450.c
>> index f26c7eccb62e7eb8dbd022e2f01fa496eb570b3f..b50a14547336580de88a741f1d33b126e9daa848 100644
>> --- a/drivers/clk/qcom/videocc-sm8450.c
>> +++ b/drivers/clk/qcom/videocc-sm8450.c
>> @@ -437,6 +437,10 @@ static int video_cc_sm8450_probe(struct platform_device *pdev)
>>       struct regmap *regmap;
>>       int ret;
>>   +    ret = qcom_cc_attach_pds(&pdev->dev, &video_cc_sm8450_desc);
>> +    if (ret)
>> +        return ret;
>> +
>>       ret = devm_pm_runtime_enable(&pdev->dev);
>>       if (ret)
>>           return ret;
>> diff --git a/drivers/clk/qcom/videocc-sm8550.c b/drivers/clk/qcom/videocc-sm8550.c
>> index 7c25a50cfa970dff55d701cb24bc3aa5924ca12d..d4b223d1392f0721afd1b582ed35d5061294079e 100644
>> --- a/drivers/clk/qcom/videocc-sm8550.c
>> +++ b/drivers/clk/qcom/videocc-sm8550.c
>> @@ -542,6 +542,10 @@ static int video_cc_sm8550_probe(struct platform_device *pdev)
>>       int ret;
>>       u32 sleep_clk_offset = 0x8140;
>>   +    ret = qcom_cc_attach_pds(&pdev->dev, &video_cc_sm8550_desc);
>> +    if (ret)
>> +        return ret;
>> +
>>       ret = devm_pm_runtime_enable(&pdev->dev);
>>       if (ret)
>>           return ret;
>>
> 
> What's the difference between doing the attach here or doing it in really_probe() ?
> 
> There doesn't seem to be any difference except that we will have an additional delay introduced.
> 
> Are you describing a race condition ?
> 
> I don't see _logic_ here to moving the call into the controller's higher level probe.
> 
> Can you describe some more ?

I think this is a sane course of action:

1. associate pll config with the pll (treewide change)
2. add a generic pll_configure call that parses the type
3. store PLLs to be configured in an array of dt-bindings indices
4. move PLL configuration to really_probe
5. move RPM enablement to really_probe, make it conditional to limit resource
   waste on e.g. gcc
6. move attaching GDSCs to really_probe

Konrad