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

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Date: Thu, 28 Mar 2024 15:12:44 +0530
From: "Satya Priya Kakitapalli (Temp)" <quic_skakitap@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: 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>,
        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 3/8/2024 5:24 PM, Dmitry Baryshkov wrote:
> On Fri, 8 Mar 2024 at 12:47, Satya Priya Kakitapalli (Temp)
> <quic_skakitap@...cinc.com> wrote:
>>
>> 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.
> Please consider using pm_clk instead. This is a cleaner solution
> compared to keeping the clocks always on.


In this case i think we cannot use pm_clk because, the clock that we are 
trying to keep always on here belongs to same camcc and it is not 
possible to create a PM dependency with the same dev that is camcc itself.


>>> 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>
>