netdev - Re: [PATCH net-next 1/2] net: pcs: xpcs: remove double-read of link state when using AN

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Message-ID: <0f7be52d197fee7f643217341b057185b7e9f9d1.camel@microchip.com>
Date:   Fri, 17 Mar 2023 09:59:42 +0100
From:   Steen Hegelund <steen.hegelund@...rochip.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
CC:     Andrew Lunn <andrew@...n.ch>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Jonathan McDowell <noodles@...th.li>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "Paolo Abeni" <pabeni@...hat.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/2] net: pcs: xpcs: remove double-read of link
 state when using AN

Hi Russell,

On Thu, 2023-03-16 at 16:12 +0000, Russell King (Oracle) wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> content is safe
> 
> On Thu, Mar 16, 2023 at 10:44:48AM +0100, Steen Hegelund wrote:
> > Hi Russell,
> > 
> > 
> > On Wed, 2023-03-15 at 14:46 +0000, Russell King (Oracle) wrote:
> > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> > > content is safe
> > > 
> > > Phylink does not want the current state of the link when reading the
> > > PCS link state - it wants the latched state. Don't double-read the
> > > MII status register. Phylink will re-read as necessary to capture
> > > transient link-down events as of dbae3388ea9c ("net: phylink: Force
> > > retrigger in case of latched link-fail indicator").
> > > 
> > > The above referenced commit is a dependency for this change, and thus
> > > this change should not be backported to any kernel that does not
> > > contain the above referenced commit.
> > > 
> > > Fixes: fcb26bd2b6ca ("net: phy: Add Synopsys DesignWare XPCS MDIO module")
> > > Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> > > ---
> > >  drivers/net/pcs/pcs-xpcs.c | 13 ++-----------
> > >  1 file changed, 2 insertions(+), 11 deletions(-)
> > > 
> > > diff --git a/drivers/net/pcs/pcs-xpcs.c b/drivers/net/pcs/pcs-xpcs.c
> > > index bc428a816719..04a685353041 100644
> > > --- a/drivers/net/pcs/pcs-xpcs.c
> > > +++ b/drivers/net/pcs/pcs-xpcs.c
> > > @@ -321,7 +321,7 @@ static int xpcs_read_fault_c73(struct dw_xpcs *xpcs,
> > >         return 0;
> > >  }
> > > 
> > > -static int xpcs_read_link_c73(struct dw_xpcs *xpcs, bool an)
> > > +static int xpcs_read_link_c73(struct dw_xpcs *xpcs)
> > >  {
> > >         bool link = true;
> > >         int ret;
> > > @@ -333,15 +333,6 @@ static int xpcs_read_link_c73(struct dw_xpcs *xpcs,
> > > bool an)
> > >         if (!(ret & MDIO_STAT1_LSTATUS))
> > >                 link = false;
> > > 
> > > -       if (an) {
> > > -               ret = xpcs_read(xpcs, MDIO_MMD_AN, MDIO_STAT1);
> > > -               if (ret < 0)
> > > -                       return ret;
> > > -
> > > -               if (!(ret & MDIO_STAT1_LSTATUS))
> > > -                       link = false;
> > > -       }
> > > -
> > >         return link;
> > >  }
> > > 
> > > @@ -935,7 +926,7 @@ static int xpcs_get_state_c73(struct dw_xpcs *xpcs,
> > >         int ret;
> > > 
> > >         /* Link needs to be read first ... */
> > > -       state->link = xpcs_read_link_c73(xpcs, state->an_enabled) > 0 ? 1
> > > : 0;
> > > +       state->link = xpcs_read_link_c73(xpcs) > 0 ? 1 : 0;
> > 
> > Couldn't you just say:
> > 
> >       state->link = xpcs_read_link_c73(xpcs) > 0;
> > 
> > That should be a boolean, right?
> 
> That would be another change to the code - and consider how such a
> change would fit in this series given its description and also this
> patch.
> 
> IMHO such a change should be a separate patch - and there's plenty
> of scope for cleanups like the one you suggest in this driver.
> 
> Thanks.

OK - got that!


> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

Reviewed-by: Steen Hegelund <Steen.Hegelund@...rochip.com>

BR
Steen