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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 14 Oct 2021 14:02:43 -0700
Message-ID: <CAKwvOdm1W52TmoU5m-RokN+aZF7w4G0KUu0TcWyircWi63onsA@mail.gmail.com>
Subject: Re: [PATCH] Input: touchscreen - Avoid bitwise vs logical OR warning
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
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On Thu, Oct 14, 2021 at 1:58 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> A new warning in clang points out a few places in this driver where a
> bitwise OR is being used with boolean types:
>
> drivers/input/touchscreen.c:81:17: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
>         data_present = touchscreen_get_prop_u32(dev, "touchscreen-min-x",
>                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> This use of a bitwise OR is intentional, as bitwise operations do not
> short circuit, which allows all the calls to touchscreen_get_prop_u32()
> to happen so that the last parameter is initialized while coalescing the
> results of the calls to make a decision after they are all evaluated.
>
> To make this clearer to the compiler, use the '|=' operator to assign
> the result of each touchscreen_get_prop_u32() call to data_present,
> which keeps the meaning of the code the same but makes it obvious that
> every one of these calls is expected to happen.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1472
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Thanks for the patch!
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  drivers/input/touchscreen.c | 42 ++++++++++++++++++-------------------
>  1 file changed, 21 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/input/touchscreen.c b/drivers/input/touchscreen.c
> index dd18cb917c4d..4620e20d0190 100644
> --- a/drivers/input/touchscreen.c
> +++ b/drivers/input/touchscreen.c
> @@ -80,27 +80,27 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
>
>         data_present = touchscreen_get_prop_u32(dev, "touchscreen-min-x",
>                                                 input_abs_get_min(input, axis_x),
> -                                               &minimum) |
> -                      touchscreen_get_prop_u32(dev, "touchscreen-size-x",
> -                                               input_abs_get_max(input,
> -                                                                 axis_x) + 1,
> -                                               &maximum) |
> -                      touchscreen_get_prop_u32(dev, "touchscreen-fuzz-x",
> -                                               input_abs_get_fuzz(input, axis_x),
> -                                               &fuzz);
> +                                               &minimum);
> +       data_present |= touchscreen_get_prop_u32(dev, "touchscreen-size-x",
> +                                                input_abs_get_max(input,
> +                                                                  axis_x) + 1,
> +                                                &maximum);
> +       data_present |= touchscreen_get_prop_u32(dev, "touchscreen-fuzz-x",
> +                                                input_abs_get_fuzz(input, axis_x),
> +                                                &fuzz);
>         if (data_present)
>                 touchscreen_set_params(input, axis_x, minimum, maximum - 1, fuzz);
>
>         data_present = touchscreen_get_prop_u32(dev, "touchscreen-min-y",
>                                                 input_abs_get_min(input, axis_y),
> -                                               &minimum) |
> -                      touchscreen_get_prop_u32(dev, "touchscreen-size-y",
> -                                               input_abs_get_max(input,
> -                                                                 axis_y) + 1,
> -                                               &maximum) |
> -                      touchscreen_get_prop_u32(dev, "touchscreen-fuzz-y",
> -                                               input_abs_get_fuzz(input, axis_y),
> -                                               &fuzz);
> +                                               &minimum);
> +       data_present |= touchscreen_get_prop_u32(dev, "touchscreen-size-y",
> +                                                input_abs_get_max(input,
> +                                                                  axis_y) + 1,
> +                                                &maximum);
> +       data_present |= touchscreen_get_prop_u32(dev, "touchscreen-fuzz-y",
> +                                                input_abs_get_fuzz(input, axis_y),
> +                                                &fuzz);
>         if (data_present)
>                 touchscreen_set_params(input, axis_y, minimum, maximum - 1, fuzz);
>
> @@ -108,11 +108,11 @@ void touchscreen_parse_properties(struct input_dev *input, bool multitouch,
>         data_present = touchscreen_get_prop_u32(dev,
>                                                 "touchscreen-max-pressure",
>                                                 input_abs_get_max(input, axis),
> -                                               &maximum) |
> -                      touchscreen_get_prop_u32(dev,
> -                                               "touchscreen-fuzz-pressure",
> -                                               input_abs_get_fuzz(input, axis),
> -                                               &fuzz);
> +                                               &maximum);
> +       data_present |= touchscreen_get_prop_u32(dev,
> +                                                "touchscreen-fuzz-pressure",
> +                                                input_abs_get_fuzz(input, axis),
> +                                                &fuzz);
>         if (data_present)
>                 touchscreen_set_params(input, axis, 0, maximum, fuzz);
>
>
> base-commit: a41392e0877a271007e9209e63c34cab7527eb43
> --
> 2.33.1.637.gf443b226ca
>
>


-- 
Thanks,
~Nick Desaulniers