linux-kernel - Re: [PATCH] net: tulip: avoid unused variable warning

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Message-ID: <20250312131433.GS4159220@kernel.org>
Date: Wed, 12 Mar 2025 14:14:33 +0100
From: Simon Horman <horms@...nel.org>
To: deller@...nel.org
Cc: netdev@...r.kernel.org, linux-parisc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Helge Deller <deller@....de>
Subject: Re: [PATCH] net: tulip: avoid unused variable warning

On Sun, Mar 09, 2025 at 10:42:38PM +0100, deller@...nel.org wrote:
> From: Helge Deller <deller@....de>
> 
> When compiling with W=1 and CONFIG_TULIP_MWI=n one gets this warning:
>  drivers/net/ethernet/dec/tulip/tulip_core.c: In function ‘tulip_init_one’:
>  drivers/net/ethernet/dec/tulip/tulip_core.c:1309:22: warning: variable ‘force_csr0’ set but not used
> 
> Avoid it by annotating the variable __maybe_unused, which seems to be
> the easiest solution.
> 
> Signed-off-by: Helge Deller <deller@....de>

Hi Helge,

A few thoughts on this:

Firstly, thanks for your patch, which I agree addresses the problem you
have described.

However, AFAIK, this is a rather old driver and I'm not sure that
addressing somewhat cosmetic problems are worth the churn they cause:
maybe it's best to leave it be.

But if we do want to fix this problem, I do wonder if the following
solution, which leverages IS_ENABLED, is somehow nicer as
it slightly reduces the amount of conditionally compiled code,
thus increasing compile test coverage.

diff --git a/drivers/net/ethernet/dec/tulip/tulip_core.c b/drivers/net/ethernet/dec/tulip/tulip_core.c
index 27e01d780cd0..75eac18ff246 100644
--- a/drivers/net/ethernet/dec/tulip/tulip_core.c
+++ b/drivers/net/ethernet/dec/tulip/tulip_core.c
@@ -1177,7 +1177,6 @@ static void set_rx_mode(struct net_device *dev)
 	iowrite32(csr6, ioaddr + CSR6);
 }
 
-#ifdef CONFIG_TULIP_MWI
 static void tulip_mwi_config(struct pci_dev *pdev, struct net_device *dev)
 {
 	struct tulip_private *tp = netdev_priv(dev);
@@ -1251,7 +1250,6 @@ static void tulip_mwi_config(struct pci_dev *pdev, struct net_device *dev)
 		netdev_dbg(dev, "MWI config cacheline=%d, csr0=%08x\n",
 			   cache, csr0);
 }
-#endif
 
 /*
  *	Chips that have the MRM/reserved bit quirk and the burst quirk. That
@@ -1463,10 +1461,9 @@ static int tulip_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 
 	INIT_WORK(&tp->media_work, tulip_tbl[tp->chip_id].media_task);
 
-#ifdef CONFIG_TULIP_MWI
-	if (!force_csr0 && (tp->flags & HAS_PCI_MWI))
+	if (IS_ENABLED(CONFIG_TULIP_MWI) && !force_csr0 &&
+	    (tp->flags & HAS_PCI_MWI))
 		tulip_mwi_config (pdev, dev);
-#endif
 
 	/* Stop the chip's Tx and Rx processes. */
 	tulip_stop_rxtx(tp);