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

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Date: Fri, 8 Mar 2024 13:54:02 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: "Satya Priya Kakitapalli (Temp)" <quic_skakitap@...cinc.com>
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 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.

> > 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>
>


-- 
With best wishes
Dmitry