linux-kernel - Re: [PATCH 4/9] staging: panel: Use a macro for checking module params state

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Message-ID: <20141118211844.GG26514@1wt.eu>
Date:	Tue, 18 Nov 2014 22:18:44 +0100
From:	Willy Tarreau <w@....eu>
To:	Mariusz Gorski <marius.gorski@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] staging: panel: Use a macro for checking module params state

On Tue, Nov 18, 2014 at 09:56:09PM +0100, Mariusz Gorski wrote:
> Avoid values comparison and use a macro instead that checks
> whether module param has been set by the user to some value
> at loading time.
> 
> Signed-off-by: Mariusz Gorski <marius.gorski@...il.com>
> ---
>  drivers/staging/panel/panel.c | 88 ++++++++++++++++++++++---------------------
>  1 file changed, 45 insertions(+), 43 deletions(-)
> 
> diff --git a/drivers/staging/panel/panel.c b/drivers/staging/panel/panel.c
> index 1b4a211..97fc4ca 100644
> --- a/drivers/staging/panel/panel.c
> +++ b/drivers/staging/panel/panel.c
> @@ -135,6 +135,8 @@
>  
>  #define NOT_SET			-1
>  
> +#define IS_NOT_SET(x)	(x == NOT_SET)
> +
>  /* macros to simplify use of the parallel port */
>  #define r_ctr(x)        (parport_read_control((x)->port))
>  #define r_dtr(x)        (parport_read_data((x)->port))
> @@ -1411,29 +1413,29 @@ static void lcd_init(void)
>  	switch (lcd_type) {
>  	case LCD_TYPE_OLD:
>  		/* parallel mode, 8 bits */
> -		if (lcd_proto < 0)
> +		if (IS_NOT_SET(lcd_proto))
>  			lcd_proto = LCD_PROTO_PARALLEL;
> -		if (lcd_charset < 0)
> +		if (IS_NOT_SET(lcd_charset))
>  			lcd_charset = LCD_CHARSET_NORMAL;
>  		if (lcd_e_pin == PIN_NOT_SET)
>  			lcd_e_pin = PIN_STROBE;
>  		if (lcd_rs_pin == PIN_NOT_SET)
>  			lcd_rs_pin = PIN_AUTOLF;
>  
> -		if (lcd_width < 0)
> +		if (IS_NOT_SET(lcd_width))
>  			lcd_width = 40;
(...)

I'm not convinced at all by the increased readability of this one.
To me it adds obfuscation since I have to look for the macro definition
to see how it checks whether the type is set or not.

I think you'd rather simply open-code the macro here and keep the natural
comparison. The fields were already initialized to the NOT_SET value, better
check agaist the same value here especially since it matches other tests as
well. That would give :

-		if (lcd_proto < 0)
+		if (lcd_proto == NOT_SET)
  			lcd_proto = LCD_PROTO_PARALLEL;

etc...  To me it's more readable.

Willy

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