linux-kernel - Re: [PATCH] backlight: lm3639: Unconditionally call led_classdev

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Message-ID: <CAKwvOdnj5M1xTKue7qZCV-2=hLTATnB-J1QOVvaVVa+8h+vq4A@mail.gmail.com>
Date:   Fri, 21 Sep 2018 15:48:50 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     lee.jones@...aro.org, daniel.thompson@...aro.org,
        jingoohan1@...il.com, b.zolnierkie@...sung.com,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] backlight: lm3639: Unconditionally call led_classdev_unregister

On Fri, Sep 21, 2018 at 1:23 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> Clang warns that the address of a pointer will always evaluated as true
> in a boolean context.
>
> drivers/video/backlight/lm3639_bl.c:403:14: warning: address of
> 'pchip->cdev_torch' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>         if (&pchip->cdev_torch)
>         ~~   ~~~~~~~^~~~~~~~~~
> drivers/video/backlight/lm3639_bl.c:405:14: warning: address of
> 'pchip->cdev_flash' will always evaluate to 'true'
> [-Wpointer-bool-conversion]
>         if (&pchip->cdev_flash)
>         ~~   ~~~~~~~^~~~~~~~~~
> 2 warnings generated.
>
> These statements have been present since 2012, introduced by
> commit 0f59858d5119 ("backlight: add new lm3639 backlight
> driver"). Given that they have been called unconditionally since
> then presumably without any issues, removing the always true if
> statements to fix the warnings without any real world changes.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/119
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>
> Alternatively, it's possible the address wasn't supposed to be taken or
> the dev in these structs should be checked instead. I don't have this
> hardware to make that call so I would appreciate some review and
> opinions on what was intended here.
>
> Thanks!
>
>  drivers/video/backlight/lm3639_bl.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/video/backlight/lm3639_bl.c b/drivers/video/backlight/lm3639_bl.c
> index cd50df5807ea..086611c7bc03 100644
> --- a/drivers/video/backlight/lm3639_bl.c
> +++ b/drivers/video/backlight/lm3639_bl.c
> @@ -400,10 +400,8 @@ static int lm3639_remove(struct i2c_client *client)
>
>         regmap_write(pchip->regmap, REG_ENABLE, 0x00);
>
> -       if (&pchip->cdev_torch)
> -               led_classdev_unregister(&pchip->cdev_torch);
> -       if (&pchip->cdev_flash)
> -               led_classdev_unregister(&pchip->cdev_flash);
> +       led_classdev_unregister(&pchip->cdev_torch);
> +       led_classdev_unregister(&pchip->cdev_flash);

led_classdev_unregister() requires that its arg is non-null (as it
dereferences it without any kind of check).  It's not clear that
i2c_get_clientdata() can never return a null pointer, so I think all
references to pchip in this function should instead be guarded with a
null check.  Would you mind making that change and sending a v2?

>         if (pchip->bled)
>                 device_remove_file(&(pchip->bled->dev), &dev_attr_bled_mode);
>         return 0;
> --
> 2.19.0
>


-- 
Thanks,
~Nick Desaulniers