linux-kernel - Re: [PATCH v2 4/5] clk: qcom: camcc-sc8280xp: Add sc8280xp CAMCC

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Date:   Mon, 2 Oct 2023 11:17:35 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        andersson@...nel.org, agross@...nel.org, mturquette@...libre.com,
        sboyd@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        jonathan@...ek.ca, quic_tdas@...cinc.com,
        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
Subject: Re: [PATCH v2 4/5] clk: qcom: camcc-sc8280xp: Add sc8280xp CAMCC



On 10/1/23 00:53, Bryan O'Donoghue wrote:
> On 30/09/2023 17:39, Konrad Dybcio wrote:
>>
>>> +static struct clk_branch camcc_gdsc_clk = {
>>> +    .halt_reg = 0xc1e4,
>>> +    .halt_check = BRANCH_HALT,
>>> +    .clkr = {
>>> +        .enable_reg = 0xc1e4,
>>> +        .enable_mask = BIT(0),
>>> +        .hw.init = &(struct clk_init_data){
>>> +            .name = "camcc_gdsc_clk",
>>> +            .parent_hws = (const struct clk_hw*[]){
>>> +                &camcc_xo_clk_src.clkr.hw,
>>> +            },
>>> +            .num_parents = 1,
>>> +            .flags = CLK_IS_CRITICAL | CLK_SET_RATE_PARENT,
>> "meh"
>>
>> Is this clock only necessary for the GDSC to turn on?
> 
> Most of this code is autogenerated in downstream as I understand it a 
> script is run against some definition the RTL one would hope.
> 
> I think that is probably how the gdsc clocks for the camcc are marked 
> like this upstream already too.
> 
> grep CRITICAL drivers/clk/qcom/*camcc*
> drivers/clk/qcom/camcc-sc7280.c:            .flags = CLK_IS_CRITICAL | 
> CLK_SET_RATE_PARENT,
> drivers/clk/qcom/camcc-sm8250.c:            .flags = CLK_IS_CRITICAL | 
> CLK_SET_RATE_PARENT,
> drivers/clk/qcom/camcc-sm8450.c:            .flags = CLK_IS_CRITICAL | 
> CLK_SET_RATE_PARENT,
> 
> I can tell you what clocks this clock but I can't tell you where that 
> clock routes too, so the best/only source of information I have is the 
> flag that comes from the autogenerated downstream code.
> 
> I think the safe thing to do is to leave the flag as is TBH.
Safe yes, good no.

Clocks with this flag prevent the clock controller device from
entering runtime suspend, which causes a dangling vote on RPMh
and prevents system power collapse.

Konrad