linux-kernel - Re: [PATCH] net: mlxsw: avoid unused variable warnings

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Message-Id: <20160323.143805.310789862506977932.davem@davemloft.net>
Date:	Wed, 23 Mar 2016 14:38:05 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	andrew@...n.ch
Cc:	arnd@...db.de, jiri@...lanox.com, idosch@...lanox.com,
	eladr@...lanox.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: mlxsw: avoid unused variable warnings

From: Andrew Lunn <andrew@...n.ch>
Date: Wed, 23 Mar 2016 17:51:11 +0100

> On Wed, Mar 23, 2016 at 05:37:38PM +0100, Arnd Bergmann wrote:
>> dev_dbg_ratelimited() is a macro that ignores its arguments when DEBUG is
>> not set, which can lead to unused variable warnings:
>> 
>> ethernet/mellanox/mlxsw/pci.c: In function 'mlxsw_pci_cqe_sdq_handle':
>> ethernet/mellanox/mlxsw/pci.c:646:18: warning: unused variable 'pdev' [-Wunused-variable]
>> ethernet/mellanox/mlxsw/pci.c: In function 'mlxsw_pci_cqe_rdq_handle':
>> ethernet/mellanox/mlxsw/pci.c:671:18: warning: unused variable 'pdev' [-Wunused-variable]
>> 
>> This changes the mlxsw driver to remove the local variables we get
>> warnings for and instead pass the device directly into the API.
> 
> Hi Arnd
> 
> Would it not be better to fix the macro?
> 
> I think the issue is that dev_dbg_ratelimited calls no_printk(),
> without making use of dev. So how about:
> 
> #define dev_dbg_ratelimited(dev, fmt, ...)                              \
> ({                                                                      \
>         if (0)                                                          \
>                 dev_printk(KERN_DEBUG, dev, fmt, ##__VA_ARGS__);        \
> })
> 
> This follows the pattern for other macros for when DEBUG is not defined.

Yeah, this is probably a better way to fix this problem.