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

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Date:   Tue, 17 Sep 2019 13:38:53 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        mturquette@...libre.com, robh+dt@...nel.org
Cc:     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,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: Re: [PATCH v5 2/8] clk: Warn if clk_init_data is not zero initialized

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. 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.

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