linux-kernel - Re: [PATCH 3/4] clk: qcom: clk-krait: add hw_parent check for div2_round

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Date:   Fri, 29 Apr 2022 18:22:50 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Sricharan R <sricharan@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] clk: qcom: clk-krait: add hw_parent check for div2_round_rate

On Fri, 29 Apr 2022 at 18:08, Ansuel Smith <ansuelsmth@...il.com> wrote:
>
> On Fri, Apr 29, 2022 at 05:53:32PM +0300, Dmitry Baryshkov wrote:
> > On 29/04/2022 15:01, Ansuel Smith wrote:
> > > Check if hw_parent is present before calculating the round_rate to
> > > prevent kernel panic. On error -EINVAL is reported.
> > >
> > > Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> >
> > I see that other clock drivers do not perform this check. Which path leads
> > to this oops?
> >
>
> This comes from qsdk patches so I apologize in advance about this.

Ugh. If it comes from the code authored by somebody else, it'd be
better to note this (by using the From or Co-developed-by tags).
At the very least (if the author is unknown) you can mention the
origin of the patch (qsdk) in the commit message.

>
> Anyway I'm checking the code and krait-cc is the only user of
> krait_div2_clk_ops. That user have as parent only hfpll_something that
> is declared by gcc. Now hfpll can also be declared in dts with a
> dedicated driver so I wonder if the problem is there in the case when
> hfpll is declared in dts and is probed after krait-cc. This is not the
> case for ipq8064 but I wonder if qsdk have other krait based device that
> have a configuration with hfpll declared in dts.

On msm8974 (and maybe others) the hfpll should be driven by the
separate hfpll driver.

>
> In short you are right and in our current code the check is uselss and
> I'm positive about dropping this patch but I do wonder if downstream
> there is an actual use of this. Don't know how to proceed. Any hint?

I'd say, let's drop it for now unless Stephen or Bjorn tell us that
it's a valid check.

>
> > > ---
> > >   drivers/clk/qcom/clk-krait.c | 7 ++++++-
> > >   1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/clk/qcom/clk-krait.c b/drivers/clk/qcom/clk-krait.c
> > > index 90046428693c..6c367ad6506a 100644
> > > --- a/drivers/clk/qcom/clk-krait.c
> > > +++ b/drivers/clk/qcom/clk-krait.c
> > > @@ -84,7 +84,12 @@ EXPORT_SYMBOL_GPL(krait_mux_clk_ops);
> > >   static long krait_div2_round_rate(struct clk_hw *hw, unsigned long rate,
> > >                               unsigned long *parent_rate)
> > >   {
> > > -   *parent_rate = clk_hw_round_rate(clk_hw_get_parent(hw), rate * 2);
> > > +   struct clk_hw *hw_parent = clk_hw_get_parent(hw);
> > > +
> > > +   if (!hw_parent)
> > > +           return -EINVAL;
> > > +
> > > +   *parent_rate = clk_hw_round_rate(hw_parent, rate * 2);
> > >     return DIV_ROUND_UP(*parent_rate, 2);
> > >   }
> >
> >
> > --
> > With best wishes
> > Dmitry
>
> --
>         Ansuel



-- 
With best wishes
Dmitry