linux-kernel - Re: [PATCH 11/18] tty: serial: samsung: don't compare with zero an if (bitwise expression)

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Date: Tue, 16 Jan 2024 12:38:02 -0600
From: Sam Protsenko <semen.protsenko@...aro.org>
To: Tudor Ambarus <tudor.ambarus@...aro.org>
Cc: krzysztof.kozlowski@...aro.org, alim.akhtar@...sung.com, 
	gregkh@...uxfoundation.org, jirislaby@...nel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, 
	andre.draszik@...aro.org, peter.griffin@...aro.org, kernel-team@...roid.com, 
	willmcvicker@...gle.com
Subject: Re: [PATCH 11/18] tty: serial: samsung: don't compare with zero an if
 (bitwise expression)

On Wed, Jan 10, 2024 at 4:24 AM Tudor Ambarus <tudor.ambarus@...aroorg> wrote:
>
> Since an if tests the numeric value of an expression, certain coding
> shortcuts can be used. The most obvious one is writing
>     if (expression)
> instead of
>     if (expression != 0)
>
> Since our case is a bitwise expression, it's more natural and clear to
> use the ``if (expression)`` shortcut.

Maybe the author of this code:

    (ufstat & info->tx_fifomask) != 0

just wanted to outline (logically) that the result of this bitwise
operation produces FIFO length, which he checks to have non-zero
length? Mechanically of course it doesn't matter much, and I guess
everyone can understand what's going on there even without '!= 0'
part. But it looks quite intentional to me, because in the same 'if'
block the author uses this as well:

    (ufstat & info->tx_fifofull)

without any comparison operators.

>
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
> ---
>  drivers/tty/serial/samsung_tty.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> index dbbe6b8e3ceb..f2413da14b1d 100644
> --- a/drivers/tty/serial/samsung_tty.c
> +++ b/drivers/tty/serial/samsung_tty.c
> @@ -988,8 +988,7 @@ static unsigned int s3c24xx_serial_tx_empty(struct uart_port *port)
>         u32 ufcon = rd_regl(port, S3C2410_UFCON);
>
>         if (ufcon & S3C2410_UFCON_FIFOMODE) {
> -               if ((ufstat & info->tx_fifomask) != 0 ||
> -                   (ufstat & info->tx_fifofull))
> +               if ((ufstat & info->tx_fifomask) || (ufstat & info->tx_fifofull))

Does this line fit into 80 characters? If no, please rework it so it
does. I guess it's also possible to get rid of superfluous braces
there, but then the code might look confusing, and I'm not sure if
checkpatch would be ok with that.

>                         return 0;
>
>                 return 1;
> --
> 2.43.0.472.g3155946c3a-goog
>
>