linux-kernel - Re: [PATCH v5 2/8] clk: Warn if clk_init

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Message-ID: <20191020152510.GA12864@Mani-XPS-13-9360>
Date:   Sun, 20 Oct 2019 20:55:10 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     mturquette@...libre.com, robh+dt@...nel.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        haitao.suo@...main.com, darren.tsao@...main.com,
        fisher.cheng@...main.com, alec.lin@...main.com
Subject: Re: [PATCH v5 2/8] clk: Warn if clk_init_data is not zero initialized

Hi Stephen,

On Tue, Sep 17, 2019 at 01:38:53PM -0700, Stephen Boyd wrote:
> Quoting Manivannan Sadhasivam (2019-09-16 09:14:41)
> > The new implementation for determining parent map uses multiple ways
> > to pass parent info. The order in which it gets processed depends on
> > the first available member. Hence, it is necessary to zero init the
> > clk_init_data struct so that the expected member gets processed correctly.
> > So, add a warning if multiple clk_init_data members are available during
> > clk registration.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> >  drivers/clk/clk.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index c0990703ce54..7d6d6984c979 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -3497,6 +3497,14 @@ static int clk_core_populate_parent_map(struct clk_core *core)
> >         if (!num_parents)
> >                 return 0;
> >  
> > +       /*
> > +        * Check for non-zero initialized clk_init_data struct. This is
> > +        * required because, we only require one of the (parent_names/
> > +        * parent_data/parent_hws) to be set at a time. Otherwise, the
> > +        * current code would use first available member.
> > +        */
> > +       WARN_ON((parent_names && parent_data) || (parent_names && parent_hws));
> > +
> 
> This will warn for many drivers because they set clk_init_data on the
> stack and assign parent_names but let junk from the stack be assigned to
> parent_data.

Yes, I agree.

> The code uses parent_names first and then looks for
> parent_data or parent_hws because of this fact of life that we've never
> required clk_init_data to be initialized to all zero.
> 

Do you want me to just drop this patch or have any idea to make it better?

Thanks,
Mani

> >         /*
> >          * Avoid unnecessary string look-ups of clk_core's possible parents by
> >          * having a cache of names/clk_hw pointers to clk_core pointers.