From: Michal Kubecek <mkubecek@suse.cz>
To: netdev@vger.kernel.org
Cc: Andrew Lunn <andrew@lunn.ch>,
Matthew Wilcox <willy@infradead.org>,
yu kuai <yukuai3@huawei.com>,
klassert@kernel.org, davem@davemloft.net, hkallweit1@gmail.com,
jakub.kicinski@netronome.com, hslester96@gmail.com,
mst@redhat.com, yang.wei9@zte.com.cn,
linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
zhengbin13@huawei.com
Subject: Re: [PATCH] net: 3com: 3c59x: remove set but not used variable 'mii_reg1'
Date: Fri, 3 Jan 2020 19:17:01 +0100 [thread overview]
Message-ID: <20200103181701.GB22387@unicorn.suse.cz> (raw)
In-Reply-To: <20200103175318.GN1397@lunn.ch>
On Fri, Jan 03, 2020 at 06:53:18PM +0100, Andrew Lunn wrote:
> On Fri, Jan 03, 2020 at 06:46:23AM -0800, Matthew Wilcox wrote:
> > On Fri, Jan 03, 2020 at 08:19:07PM +0800, yu kuai wrote:
> > > Fixes gcc '-Wunused-but-set-variable' warning:
> > >
> > > drivers/net/ethernet/3com/3c59x.c: In function ‘vortex_up’:
> > > drivers/net/ethernet/3com/3c59x.c:1551:9: warning: variable
> > > ‘mii_reg1’ set but not used [-Wunused-but-set-variable]
> > >
> > > It is never used, and so can be removed.
> > ...
> > > if (dev->if_port == XCVR_MII || dev->if_port == XCVR_NWAY) {
> > > - mii_reg1 = mdio_read(dev, vp->phys[0], MII_BMSR);
> > > mii_reg5 = mdio_read(dev, vp->phys[0], MII_LPA);
> >
> > I know nothing about the MII interface, but in general this is not
> > a safe thing to do.
>
> Hi Matthew
>
> I fully agree about the general case. However, reading the MII_BMSR
> should not have any side affects. It would be an odd Ethernet PHY if
> it did.
>
> But I am curious why this read is here. There is a slim change the
> MDIO bus is broken, and this is a workaround. So it would be good if
> somebody dug into the history and found out when this read was added
> and if there are any comments about why it is there. Or if the usage
> of mii_reg1 as been removed at some point, and the read was not
> cleaned up.
I tried to dig a bit and found that originally (before git), there was
also
if (vortex_debug > 1)
printk(KERN_INFO "%s: MII #%d status %4.4x, link partner capability %4.4x,"
" info1 %04x, setting %s-duplex.\n",
dev->name, vp->phys[0],
mii_reg1, mii_reg5,
vp->info1, ((vp->info1 & 0x8000) || vp->full_duplex) ? "full" : "half");
The whole mii code in vortex_up() was removed by commit 125d5ce8a4e9
("[PATCH] 3c59x: use mii_check_media") and later the mdio_read() calls
were restored by commit 09ce3512dcad ("[PATCH] 3c59x: fix networking for
10base2 NICs") with "Also brought back some mii stuff to be sure that it
does not break something else", but without the debugging printk().
It's not really a proof that reading MII_BMSR was only needed for the
log message but there is a good chance it was. I'm afraid we won't be
able to find anyone who would be able to tell for sure after all those
years.
Michal
next prev parent reply other threads:[~2020-01-03 18:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-03 12:19 [PATCH] net: 3com: 3c59x: remove set but not used variable 'mii_reg1' yu kuai
2020-01-03 14:46 ` Matthew Wilcox
2020-01-03 14:59 ` Michal Kubecek
2020-01-03 17:53 ` Andrew Lunn
2020-01-03 18:17 ` Michal Kubecek [this message]
2020-01-03 19:13 ` Vladimir Oltean
2020-01-03 19:17 ` Florian Fainelli
2020-01-03 19:37 ` Andrew Lunn
[not found] ` <CAP8WD_a6QJNz2mUpz_eCaNReoZKVAdL0TpoF-m+gA4VPWRrrMg@mail.gmail.com>
2020-01-03 20:03 ` tedheadster
2020-01-06 12:48 ` yukuai (C)
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