linux-kernel - Re: [PATCH 4/5] clk: qcom: Add camera clock controller driver for SM8150

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Date: Fri, 8 Mar 2024 16:16:14 +0530
From: "Satya Priya Kakitapalli (Temp)" <quic_skakitap@...cinc.com>
To: Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        "Michael
 Turquette" <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Abhishek Sahu <absahu@...eaurora.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley
	<conor+dt@...nel.org>
CC: Stephen Boyd <sboyd@...eaurora.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, Ajit Pandey <quic_ajipan@...cinc.com>,
        "Imran
 Shaik" <quic_imrashai@...cinc.com>,
        Taniya Das <quic_tdas@...cinc.com>,
        Jagadeesh Kona <quic_jkona@...cinc.com>
Subject: Re: [PATCH 4/5] clk: qcom: Add camera clock controller driver for
 SM8150


On 3/6/2024 7:25 PM, Bryan O'Donoghue wrote:
> On 06/03/2024 08:30, Satya Priya Kakitapalli (Temp) wrote:
>>>
>>> Anyway I suspect the right thing to do is to define a 
>>> titan_top_gdsc_clk with shared ops to "park" the GDSC clock to 19.2 
>>> MHz instead of turning it off.
>>>
>>> You can get rid of the hard-coded always-on and indeed represent the 
>>> clock in /sysfs - which is preferable IMO to just whacking registers 
>>> to keep clocks always-on in probe anyway.
>>>
>>> Please try to define the titan_top_gdsc_clk as a shared_ops clock 
>>> instead of hard coding to always on.
>>>
>>
>> Defining the gdsc clk allows consumers to control it, we do not want 
>> this clock to be disabled/controlled from consumers. Hence it is 
>> better to not model this clock and just keep it always on from probe.
>
> Not if you mark it critical
>

Marking the clock as critical keeps the associated power domain 
always-on which impacts power. For this reason we are not using 
CLK_IS_CRITICAL and instead making them always on from probe.


> static struct clk_branch cam_cc_gdsc_clk = {
>         .halt_reg = 0xc1e4,
>         .halt_check = BRANCH_HALT,
>         .clkr = {
>                 .enable_reg = 0xc1e4,
>                 .enable_mask = BIT(0),
>                 .hw.init = &(struct clk_init_data){
>                         .name = "cam_cc_gdsc_clk",
>                         .parent_hws = (const struct clk_hw*[]){
>                                 &cam_cc_xo_clk_src.clkr.hw
>                         },
>                         .num_parents = 1,
>                         .flags = CLK_IS_CRITICAL | CLK_SET_RATE_PARENT,
>                         .ops = &clk_branch2_ops,
>                 },
>         },
> };
>
> and then add this to your camss clocks
>
> <&clock_camcc CAM_CC_GDSC_CLK>;
>
> The practice we have of just whacking clocks always-on in the probe() 
> of the clock driver feels lazy to me, leaving the broken cleanups we 
> have aside.
>
> As a user of the system I'd rather see correct/complete data in 
> /sys/kernel/debug/clk/clk_summary
>
> Anyway I'm fine with setting the clock always on, I can always send 
> out a series to address this bug-bear myself.
>
> So yeah just fix the cleanup and then please feel free to add my
>
> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>