linux-kernel - Re: [RFC v1 02/11] clk: qcom: rcg2: Add support for flags

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Date:   Thu, 17 Jun 2021 15:37:37 +0200
From:   Robert Foss <robert.foss@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        Taniya Das <tdas@...eaurora.org>,
        MSM <linux-arm-msm@...r.kernel.org>,
        "open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Vinod Koul <vinod.koul@...aro.org>
Subject: Re: [RFC v1 02/11] clk: qcom: rcg2: Add support for flags

On Wed, 16 Jun 2021 at 18:07, Dmitry Baryshkov
<dmitry.baryshkov@...aro.org> wrote:
> > diff --git a/drivers/clk/qcom/clk-rcg.h b/drivers/clk/qcom/clk-rcg.h
> > index 99efcc7f8d88..a1f05281d950 100644
> > --- a/drivers/clk/qcom/clk-rcg.h
> > +++ b/drivers/clk/qcom/clk-rcg.h
> > @@ -149,6 +149,10 @@ struct clk_rcg2 {
> >       const struct freq_tbl   *freq_tbl;
> >       struct clk_regmap       clkr;
> >       u8                      cfg_off;
> > +     u8                      flags;
> > +#define FORCE_ENABLE_RCG     BIT(0)
> > +#define HW_CLK_CTRL_MODE     BIT(1)
>
> Downstream also has these flags for 8250, but the upstream driver ended
> up not using them for the dispcc clocks. Could you please check that you
> realy need HW_CLK_CTRL for dispcc clocks?

HW_CLK_CTRL being flagged in dispcc causes the CFG_HW_CLK_CTRL flag to
be set in the RCG_CFG registers of dispcc.

This flag simply marks the clock as having hardware control enabled or disabled.

As for the question if it is really needed, I can't answer that since
no documentation or downstream comments explain the exact behaviour.
As far as I know the only way to figure out if it is required is
disabling the flag and checking for bugs. I did find this[1] patch,
which enabled HW_CLK_CTRL_MODE.

Should I err on the side of the downstream implementation, or try to
create a minimum functional driver based on the downstream driver?

[1] https://patchwork.kernel.org/project/linux-arm-msm/patch/1514877987-8082-2-git-send-email-anischal@codeaurora.org/