linux-kernel - Re: [Intel-wired-lan] [PATCH linux-next] e1000: Remove redundant statement

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Message-ID: <20211021070937.GA9814@kernel.org>
Date:   Thu, 21 Oct 2021 09:09:40 +0200
From:   Simon Horman <horms@...nel.org>
To:     Jesse Brandeburg <jesse.brandeburg@...il.com>
Cc:     luo penghao <cgel.zte@...il.com>,
        NetDEV list <netdev@...r.kernel.org>,
        Zeal Robot <zealci@....com.cn>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        intel-wired-lan@...ts.osuosl.org, Jakub Kicinski <kuba@...nel.org>,
        luo penghao <luo.penghao@....com.cn>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH linux-next] e1000: Remove redundant
 statement

On Wed, Oct 20, 2021 at 11:08:11AM -0700, Jesse Brandeburg wrote:
> Apologies for the duplicates, mail from my intel account going out
> through outlook.com is not being delivered.
> 
> On Wed, Oct 20, 2021 at 7:00 AM Simon Horman <horms@...nel.org> wrote:
> 
> > > Value stored to 'ctrl_reg' is never read.
> >
> > I agree this does seem to be the case.
> >
> > > Reported-by: Zeal Robot <zealci@....com.cn>
> > > Signed-off-by: luo penghao <luo.penghao@....com.cn>
> >
> > Reviewed-by: Simon Horman <horms@...nel.org>
> 
> Thanks for the review, but (davem/kuba) please do not apply.

Thanks, and sorry for misunderstanding the patch.

> 
> > > @@ -1215,8 +1215,6 @@ static int e1000_integrated_phy_loopback(struct e1000_adapter *adapter)
> > >               e1000_write_phy_reg(hw, PHY_CTRL, 0x8140);
> > >       }
> > >
> > > -     ctrl_reg = er32(CTRL);
> 
> Thanks for your patch, but this change is not safe. you're removing a
> read that could do two things. The first is that the read "flushes"
> the write just above to PCI (it's a PCI barrier), and the second is
> that the read can have some side effects.
> 
> If this change must be done, the code should be to remove the
> assignment to ctrl_reg, but leave the read, so the line would just
> look like:
>         er32(CTRL);
> 
> This will get rid of the warning and not change the flow from the
> hardware perspective.
> 
> > > -
> > >       /* force 1000, set loopback */
> > >       e1000_write_phy_reg(hw, PHY_CTRL, 0x4140);
> > >
> 
> Please do not apply this.
>