linux-kernel - Re: [PATCH 4.19 6/6] Input: touchscreen - avoid bitwise vs logical OR warning

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Message-ID: <YcBiFomrxSw1eEUB@kroah.com>
Date:   Mon, 20 Dec 2021 11:59:34 +0100
From:   Greg KH <greg@...ah.com>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org, clang-built-linux@...glegroups.com,
        ulli.kroll@...glemail.com, linux@...linux.org.uk,
        linux-arm-kernel@...ts.infradead.org, amitkarwar@...il.com,
        nishants@...vell.com, gbhat@...vell.com, huxinming820@...il.com,
        kvalo@...eaurora.org, linux-wireless@...r.kernel.org,
        rostedt@...dmis.org, mingo@...hat.com, dmitry.torokhov@...il.com,
        ndesaulniers@...gle.com, nathan@...nel.org,
        linux-input@...r.kernel.org
Subject: Re: [PATCH 4.19 6/6] Input: touchscreen - avoid bitwise vs logical
 OR warning

On Fri, Dec 17, 2021 at 03:41:19PM +0100, Anders Roxell wrote:
> From: Nathan Chancellor <nathan@...nel.org>
> 
> commit a02dcde595f7cbd240ccd64de96034ad91cffc40 upstream.
> 
> 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.
> 
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Link: https://lore.kernel.org/r/20211014205757.3474635-1-nathan@kernel.org
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> ---
>  drivers/input/touchscreen/of_touchscreen.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)

Also needed in 5.10.y and 5.4.y.

Please be more careful next time.