linux-kernel - Re: [PATCH v1] clk: mediatek: assign the initial value to clk_init_data of mtk

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Message-ID: <8aa4acd2-dcc3-1eb8-e16f-b4e987808602@gmail.com>
Date:   Tue, 26 May 2020 17:42:22 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Weiyi Lu <weiyi.lu@...iatek.com>
Cc:     Nicolas Boichat <drinkcat@...omium.org>,
        Stephen Boyd <sboyd@...nel.org>,
        James Liao <jamesjj.liao@...iatek.com>,
        srv_heupstream@...iatek.com, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Fan Chen <fan.chen@...iatek.com>,
        linux-mediatek@...ts.infradead.org,
        Owen Chen <owen.chen@...iatek.com>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1] clk: mediatek: assign the initial value to
 clk_init_data of mtk_mux

Hi Weiyi,

On 26/05/2020 04:43, Weiyi Lu wrote:
> On Mon, 2020-05-25 at 11:08 +0200, Matthias Brugger wrote:
>>
>> On 25/05/2020 08:41, Weiyi Lu wrote:
>>> It'd be dangerous when struct clk_core have new memebers.
>>> Add the missing initial value to clk_init_data.
>>>
>>
>> Sorry I don't really understand this commit message, can please explain.
>> In any case if this is a problem, then we probably we should fix it for all drivers.
>> Apart from drivers/clk/mediatek/clk-cpumux.c
>>
> 
> Actually, we were looking into an android kernel patch "ANDROID: GKI:
> clk: Add support for voltage voting" [1]
> 
> In this patch, there adds a new member struct clk_vdd_class	*vdd_class;
> in struct clk_init_data and struct clk_core
> 
> And then in clk_register(...)
> core->vdd_class = hw->init->vdd_class;
> 
> In many clock APIs, it will check the core->vdd_class to select the
> correct control flow.
> So, if we don't assign an initial value to clk_init_data of mtk_mux
> clock type, something might go wrong. And assigning an initial value
> might be the easiest and good way to avoid such problem if any new clock
> support added in the future.
> 

Thanks for your explanation. You mean that as clk_init_data is on the stack it
can have random values, and would lead to the fact that vdd_class is interpreted
as allocated although it should be NULL.

Sounds reasonable to me. You might want to resend with a better commit message.
Feel free to add my

Reviewed-by: Matthias Brugger <matthias.bgg@...il.com>

Regards,
Matthias

> [1] https://android-review.googlesource.com/c/kernel/common/+/1278046
> 
>> It's a widely used pattern:
>> $ git grep "struct clk_init_data init;"| wc -l
>> 235
>>
>> Regards,
>> Matthias
>>
>>> Fixes: a3ae549917f1 ("clk: mediatek: Add new clkmux register API")
>>> Cc: <stable@...r.kernel.org>
>>> Signed-off-by: Weiyi Lu <weiyi.lu@...iatek.com>
>>> ---
>>>  drivers/clk/mediatek/clk-mux.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/clk/mediatek/clk-mux.c b/drivers/clk/mediatek/clk-mux.c
>>> index 76f9cd0..14e127e 100644
>>> --- a/drivers/clk/mediatek/clk-mux.c
>>> +++ b/drivers/clk/mediatek/clk-mux.c
>>> @@ -160,7 +160,7 @@ struct clk *mtk_clk_register_mux(const struct mtk_mux *mux,
>>>  				 spinlock_t *lock)
>>>  {
>>>  	struct mtk_clk_mux *clk_mux;
>>> -	struct clk_init_data init;
>>> +	struct clk_init_data init = {};
>>>  	struct clk *clk;
>>>  
>>>  	clk_mux = kzalloc(sizeof(*clk_mux), GFP_KERNEL);
>>>
>