linux-kernel - Re: [PATCH 5/6] clk: qcom: gcc-sdm660: Account for needed adjustments in probe function

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Date:   Wed, 31 Mar 2021 18:53:06 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>,
        phone-devel@...r.kernel.org
Cc:     ~postmarketos/upstreaming@...ts.sr.ht, martin.botka@...ainline.org,
        angelogioacchino.delregno@...ainline.org,
        marijn.suijten@...ainline.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Taniya Das <tdas@...eaurora.org>,
        Craig Tatlor <ctatlor97@...il.com>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 5/6] clk: qcom: gcc-sdm660: Account for needed adjustments in probe function

Quoting Konrad Dybcio (2021-02-25 11:09:14)
> Hi and sorry for the late reply,
> 

I'm sorry too. This fell off my review queue for some time.

> 
> >> +
> >> +       /* Keep bimc gfx clock port on all the time */
> >> +       clk_prepare_enable(gcc_bimc_gfx_clk.clkr.hw.clk);
> >> +
> > Preferably just set these various bits with regmap_update_bits() during
> > probe. Also, please do it before regsitering the clks, not after.
> 
> To be fair, now I think that simply adding CLK_IS_CRITICAL flag to the clocks in question is the smartest thing to do. Magic writes don't tell a whole lot.

This is how it's been done in various other qcom clk drivers. Usually
there is a comment about what is enabled, but really it's just setting
random bits that sadly aren't already set by default.

> 
> 
> >> +       /* Set the HMSS_GPLL0_SRC for 300MHz to CPU subsystem */
> >> +       clk_set_rate(hmss_gpll0_clk_src.clkr.hw.clk, 300000000);
> > Is this not already the case?
> 
> 
> This is a mission-critical clock and we cannot trust the bootloader with setting it. Otherwise dragons might appear.
> 

What does the bootloader set it to?