netdev - Re: [PATCH net-next 4/7] drivers: net: smc911x: Fix set but unused status because of DBG macro

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Date:   Mon, 2 Nov 2020 15:48:31 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev <netdev@...r.kernel.org>, Nicolas Pitre <nico@...xnic.net>
Subject: Re: [PATCH net-next 4/7] drivers: net: smc911x: Fix set but unused
 status because of DBG macro

On Sat, 31 Oct 2020 01:49:55 +0100 Andrew Lunn wrote:
> drivers/net/ethernet/smsc/smc911x.c: In function ‘smc911x_timeout’:
> drivers/net/ethernet/smsc/smc911x.c:1251:6: warning: variable ‘status’ set but not used [-Wunused-but-set-variable]
>  1251 |  int status, mask;
> 
> The status is read in order to print it via the DBG macro. However,
> due to the way DBG is disabled, the compiler never sees it being used.
> 
> Change the DBG macro to actually make use of the passed parameters,
> and the leave the optimiser to remove the unwanted code inside the if
> (0).
> 
> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> ---
>  drivers/net/ethernet/smsc/smc911x.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/smsc/smc911x.c b/drivers/net/ethernet/smsc/smc911x.c
> index 8f748a0c057e..33d0398c182e 100644
> --- a/drivers/net/ethernet/smsc/smc911x.c
> +++ b/drivers/net/ethernet/smsc/smc911x.c
> @@ -102,7 +102,11 @@ MODULE_ALIAS("platform:smc911x");
>  
>  #define PRINTK(dev, args...)   netdev_info(dev, args)
>  #else
> -#define DBG(n, dev, args...)   do { } while (0)
> +#define DBG(n, dev, args...)			 \
> +	do {					 \
> +		if (0)				 \
> +			netdev_dbg(dev, args);	 \
> +	} while (0)

nit: since you have to respin - while (0) { } would do here.